View source for Dinosaur

{{Short description|Clade of reptiles}}
{{Other uses}}
{{Distinguish|Dinosaurus}}
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{{Use mdy dates|date=January 2022}}
{{Automatic taxobox
| name = Dinosaurs
| fossil_range = {{fossilrange|237|0|[[Late Triassic]] – [[Holocene|Present]], 233.23–0 mya | |earliest=243 |PS=(range includes [[bird]]s) }} (possible Middle Triassic record)
| image = {{Multiple image
| perrow            = 2/2/2
|total_width=330
| image1 = Sinosauropteryxfossil.jpg
| image2 = Brontosaurus_excelsus_remount_in_the_Peabody_Museum.jpg
| image3 = Natural_History_Museum,_London_Stegosaurus.jpg
| image6 = Lambeosaurus_Pacific_Museum_of_Earth.jpg
| image5 = Triceratops_Specimen_at_the_Houston_Museum_of_Natural_Science_v01.jpg
| image4 = Tyrannosaurus_Rex_Holotype.jpg
| border = infobox
}}
| image_caption = A collection of non-avian dinosaurs (clockwise from top left): ''[[Sinosauropteryx]]'' (a small feathered [[theropod]]), ''[[Brontosaurus]]'' (a [[sauropod]]), ''[[Tyrannosaurus]]'' (a large theropod), ''[[Lambeosaurus]]'' (an [[ornithopod]]), ''[[Triceratops]]'' (a [[marginocephalian]]), and ''[[Stegosaurus]]'' (a [[thyreophoran]])
| display_parents = 4
| taxon = Dinosauria
| authority = [[Richard Owen|Owen]], 1842
| subdivision_ranks = Major groups
| subdivision = *{{extinct}}[[Ornithischia]]
*[[Saurischia]]
**{{extinct}}[[Sauropodomorpha]]
**[[Theropoda]]
***Various extinct groups
***[[Aves]] (birds)
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*{{extinct}}''[[Agnosphytis]]''?
*{{extinct}}''[[Alwalkeria]]''
*{{extinct}}''[[Chilesaurus]]''
*{{extinct}}''[[Chindesaurus]]''
*{{extinct}}''[[Daemonosaurus]]''
*{{extinct}}''[[Eodromaeus]]''
*{{extinct}}''[[Nhandumirim]]''
*{{extinct}}''[[Nyasasaurus]]''?
*{{extinct}}''[[Pisanosaurus]]''?
*{{extinct}}''[[Smok (archosaur)|Smok]]''?
*{{extinct}}''[[Tawa hallae|Tawa]]''
*{{extinct}}''[[Thecospondylus]]''
*{{extinct}}[[Herrerasauria]]<ref>Matthew G. Baron; Megan E. Williams (2018). "A re-evaluation of the enigmatic dinosauriform Caseosaurus crosbyensis from the Late Triassic of Texas, USA and its implications for early dinosaur evolution". Acta Palaeontologica Polonica. 63. {{doi|10.4202/app.00372.2017}}.</ref><ref>Andrea Cau (2018). [https://www.paleoitalia.it/wp-content/uploads/2024/03/01_Cau_2018_BSPI_571.pdf "The assembly of the avian body plan: a 160-million-year long process"] {{Webarchive|url=https://web.archive.org/web/20241203102744/https://www.paleoitalia.it/wp-content/uploads/2024/03/01_Cau_2018_BSPI_571.pdf |date=December 3, 2024 }} (PDF). Bollettino della Società Paleontologica Italiana. 57 (1): 1–25. <!-- the doi is broken {{doi|10.4435/BSPI.2018.01}}.--></ref>
*{{extinct}}[[Silesauridae]]? <small>([[paraphyletic]]?)</small><ref>{{Cite journal|last1=Ferigolo|first1=Jorge|last2=Langer |first2=Max C. |date=2007|title=A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone |journal=Historical Biology |volume=19|issue=1|pages=23–33 |doi=10.1080/08912960600845767 |bibcode=2007HBio...19...23F |s2cid=85819339|issn=0891-2963}}</ref><ref>{{Cite journal |last1=Langer |first1=Max C. |last2=Ferigolo |first2=Jorge |date=2013 |title=The Late Triassic dinosauromorph ''Sacisaurus agudoensis'' (Caturrita Formation; Rio Grande do Sul, Brazil): anatomy and affinities |url=https://sp.lyellcollection.org/content/379/1/353 |journal=Geological Society, London, Special Publications |language=en |volume=379 |issue=1 |pages=353–392 |doi=10.1144/SP379.16 |bibcode=2013GSLSP.379..353L |s2cid=131414332 |issn=0305-8719 |archive-date=August 14, 2021 |access-date=March 26, 2021 |archive-url=https://web.archive.org/web/20210814015927/https://sp.lyellcollection.org/content/379/1/353 |url-status=live }}</ref><ref name="cabreira2016">{{cite journal |last1=Cabreira |first1=S.F. |last2=Kellner |first2=A.W.A.|last3=Dias-da-Silva|first3=S.|last4=da Silva |first4=L.R. |last5=Bronzati |first5=M. |last6=de Almeida Marsola |first6=J.C. |last7=Müller|first7=R.T.|last8=de Souza Bittencourt |first8=J. |last9=Batista |first9=B.J. |last10=Raugust |first10=T. |last11=Carrilho |first11=R.|date=2016|title=A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet |journal=Current Biology|volume=26|issue=22|pages=3090–3095 |doi=10.1016/j.cub.2016.09.040 |pmid=27839975 |doi-access=free |first12=A. |last12=Brodt |first13=M.C.|last13=Langer|bibcode=2016CBio...26.3090C | issn = 0960-9822}}</ref><ref>{{Cite journal |last1=Müller|first1=Rodrigo Temp |last2=Garcia |first2=Maurício Silva |date=August 26, 2020|title=A paraphyletic 'Silesauridae' as an alternative hypothesis for the initial radiation of ornithischian dinosaurs |journal=Biology Letters |volume=16 |issue=8 |article-number=20200417 |doi=10.1098/rsbl.2020.0417 |pmid=32842895|pmc=7480155|doi-access=free}}</ref>
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[[File:Neognathae.jpg|thumb|alt=montage of four birds|[[Bird]]s are avian dinosaurs, and [[Phylogenetics|phylogenetic]] [[Taxonomy (biology)|taxonomy]] includes over 11,000 extant species in the group Dinosauria.]]
'''Dinosaurs''' are<!-- Please use "are", as the scientific consensus is that birds are also dinosaurs themselves. --> a diverse group of warmblooded [[reptile]]s{{refn|group=note|name=cold-blooded|Dinosaurs (including birds) are members of the [[clade|natural group]] [[Reptilia]]. Their biology does not precisely correspond to the antiquated [[Class (biology)|class]] Reptilia of [[Linnaean taxonomy]], consisting of [[Ectotherm|cold-blooded]] [[amniote]]s without fur or feathers. As Linnaean taxonomy was formulated for modern animals prior to the study of evolution and paleontology, it fails to account for extinct animals with intermediate traits between traditional classes.}} of the [[clade]] '''Dinosauria'''. They existed through most of the [[Mesozoic]] [[Erathem|era]], first appearing early in the [[Triassic]] [[Geological period|period]]. They became the dominant terrestrial [[vertebrate]]s after the [[Triassic–Jurassic extinction event]] 201.3&nbsp;[[Million years ago|mya]] and their dominance continued throughout the [[Jurassic]] and [[Cretaceous]] periods. The [[fossil]] record shows that [[bird]]s are [[feathered dinosaurs]], [[Evolution of birds|having evolved]] from earlier [[Theropoda|theropods]] during the [[Late Jurassic]] [[epoch]], and are the only dinosaur lineage known to have survived the [[Cretaceous–Paleogene extinction event]] approximately 66&nbsp;mya. Dinosaurs can therefore be divided into '''avian dinosaurs'''—birds—and the extinct '''non-avian dinosaurs''', which are all dinosaurs other than birds.

Dinosaurs are varied from [[taxonomy (biology)|taxonomic]], [[morphology (biology)|morphological]] and [[ecological]] standpoints. Birds, at over 11,000 living [[species]], are among the most diverse groups of vertebrates. Using fossil evidence, [[paleontologists]] have identified over 900 distinct [[genera]] and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both [[Neontology|extant]] species (birds) and fossil remains. Through most of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and [[Poikilotherm|cold-blooded]]. Most [[Dinosaur renaissance|research conducted since the 1970s]], however, has indicated that dinosaurs were active animals with elevated [[metabolism]]s and numerous adaptations for social interaction. Evidence shows that all dinosaurs had erect legs similar to that of birds and many mammals, than the sprawling leg stance of cold-blooded tetrapods. Some were [[herbivorous]], others [[carnivorous]]. Evidence suggests that all dinosaurs were [[egg-laying]], and that [[nest]]-building was a trait shared by many dinosaurs, both avian and non-avian.

While dinosaurs were ancestrally [[bipedal]], many [[extinct]] groups included [[quadrupedal]] species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, and some extinct groups developed [[skeletal]] modifications such as [[Armour (anatomy)|bony armor]] and [[spine (zoology)|spines]]. While the dinosaurs' modern-day surviving avian lineage (birds) are generally small due to the constraints of flight, many non-avian dinosaurs were large-bodied—the largest [[Sauropoda|sauropod]] dinosaurs are estimated to have reached lengths of {{convert|39.7|m|ft|abbr=off|sp=us}} and heights of {{convert|18|m|ft|abbr=on|sp=us}} and were the largest land animals of all time.

The first dinosaur fossils were recognized in the early 19th century, with the name "dinosaur" (meaning "terrible lizard") being coined by Sir [[Richard Owen]] in 1842 to refer to these "great fossil lizards". Since then, mounted fossil dinosaur skeletons have been major attractions at museums worldwide, and dinosaurs have become [[Cultural depictions of dinosaurs|an enduring part of popular culture]]. The large sizes of some dinosaurs, as well as their seemingly monstrous and fantastic nature, have ensured their regular appearance in best-selling books and films, such as the ''[[Jurassic Park (franchise)|Jurassic Park]]'' franchise. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media.

==Definition==
Under [[phylogenetic nomenclature]], dinosaurs are usually defined as the group consisting of the [[most recent common ancestor]] (MRCA) of ''[[Triceratops]]'' and [[Bird#Diversification of modern birds|modern birds]] (Neornithes), and all its descendants.<ref name=MJB04dino/> It has also been suggested that Dinosauria be defined with respect to the MRCA of ''[[Megalosaurus]]'' and ''[[Iguanodon]]'', because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria.<ref name=olshevsky2000/> Both definitions cover the same known genera: Dinosauria = [[Ornithischia]] + [[Saurischia]]. This includes major groups such as [[ankylosauria]]ns (armored herbivorous quadrupeds), [[stegosauria]]ns (plated herbivorous quadrupeds), [[ceratopsia]]ns (bipedal or quadrupedal herbivores with [[neck frill]]s), [[pachycephalosauria]]ns (bipedal herbivores with thick skulls), [[Ornithopoda|ornithopod]]s (bipedal or quadrupedal herbivores including "[[Hadrosauridae|duck-bills]]"), [[Theropoda|theropod]]s (mostly bipedal carnivores and birds), and [[sauropodomorpha|sauropodomorphs]] (mostly large herbivorous quadrupeds with long necks and tails).<ref name="Letal05"/>

Birds are the sole surviving dinosaurs. In traditional [[Taxonomy (biology)|taxonomy]], birds were considered a separate [[class (biology)|class]] that had evolved from dinosaurs. However, most contemporary paleontologists reject the traditional style of classification based on anatomical similarity, in favor of [[Phylogenetics|phylogenetic]] taxonomy based on deduced ancestry, in which each group is defined as all descendants of a given founding genus.<ref>{{cite web |url=https://evolution.berkeley.edu/evolibrary/article/evo_10 |url-status=live |title=Using the tree for classification |website=Understanding Evolution |publisher=[[University of California]] |location=[[Berkeley, California|Berkeley]] |archive-url=https://web.archive.org/web/20190831003846/https://evolution.berkeley.edu/evolibrary/article/evo_10 |archive-date=August 31, 2019 |access-date=October 14, 2019}}</ref> Birds belong to the dinosaur subgroup [[Maniraptora]], which are [[Coelurosauria|coelurosaurs]], which are theropods, which are saurischians.<ref name=KP04/>

Research by Matthew G. Baron, [[David B. Norman]], and Paul M. Barrett in 2017 suggested a radical revision of dinosaurian systematics. Phylogenetic analysis by Baron et al. recovered the Ornithischia as being closer to the Theropoda than the Sauropodomorpha, as opposed to the traditional union of theropods with sauropodomorphs. This would cause sauropods and kin to fall outside traditional dinosaurs, so they re-defined Dinosauria as the last common ancestor of ''Triceratops horridus'', ''[[house sparrow|Passer domesticus]]'' and ''[[Diplodocus|Diplodocus carnegii]]'', and all of its descendants, to ensure that sauropods and kin remain included as dinosaurs. They also resurrected the clade [[Ornithoscelida]] to refer to the group containing Ornithischia and Theropoda.<ref name="NYT-20170322">{{cite news |last=Wade |first=Nicholas |author-link=Nicholas Wade |title=Shaking Up the Dinosaur Family Tree |date=March 22, 2017 |url=https://www.nytimes.com/2017/03/22/science/dinosaur-family-tree.html |url-status=live |url-access=registration |work=[[The New York Times]] |location=[[New York City|New York]] |issn=0362-4331 |archive-url=https://web.archive.org/web/20180407234942/https://www.nytimes.com/2017/03/22/science/dinosaur-family-tree.html |archive-date=April 7, 2018 |access-date=October 30, 2019}} "A version of this article appears in print on March 28, 2017, on Page D6 of the New York edition with the headline: Shaking Up the Dinosaur Family Tree."</ref><ref name="NAT-20170322">{{cite journal |last1=Baron |first1=Matthew G. |last2=Norman |first2=David B. |author-link2=David B. Norman |last3=Barrett |first3=Paul M. |year=2017 |title=A new hypothesis of dinosaur relationships and early dinosaur evolution |journal=[[Nature (journal)|Nature]] |location=London |publisher=[[Nature Research]] |volume=543 |issue=7646 |pages=501–506 |bibcode=2017Natur.543..501B |doi=10.1038/nature21700 |issn=0028-0836 |pmid=28332513 |s2cid=205254710}}</ref>

===General description===
[[File:LA-Triceratops mount-2.jpg|thumb|upright=1.15|left|''[[Triceratops]]'' skeleton, [[Natural History Museum of Los Angeles County]]]]

Using one of the above definitions, dinosaurs can be generally described as [[archosaur]]s with [[Terrestrial locomotion#Posture|hind limbs held erect beneath the body]].<ref name=DFG97/> Other prehistoric animals, including [[pterosaur]]s, [[mosasaur]]s, [[Ichthyosauria|ichthyosaur]]s, [[Plesiosauria|plesiosaurs]], and ''[[Dimetrodon]]'', while often popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs. Pterosaurs are distantly related to dinosaurs, being members of the clade [[Avemetatarsalia|Ornithodira]]. The other groups mentioned are, like dinosaurs and pterosaurs, members of [[Sauropsida]] (the reptile and bird clade), except ''Dimetrodon'' (which is a [[synapsid]]). None of them had the erect hind limb posture characteristic of true dinosaurs.<ref name=DL90/>

Dinosaurs were the dominant terrestrial vertebrates of the [[Mesozoic]] [[Era]], especially the Jurassic and Cretaceous periods. Other groups of animals were restricted in size and niches; [[mammal]]s, for example, rarely exceeded the size of a domestic cat and were generally rodent-sized carnivores of small prey.<ref name=MM97/> Dinosaurs have always been recognized as an extremely varied group: over 900 non-avian dinosaur genera have been confidently identified (2018)  with 1124 species (2016). Estimates put the total number of dinosaur genera preserved in the fossil record at 1850, nearly 75% still undiscovered,<ref name="Genera900">{{cite journal |last1=Tennant |first1=Jonathan P. |last2=Chiarenza |first2=Alfio Alessandro |last3=Baron |first3=Matthew |title=How has our knowledge of dinosaur diversity through geologic time changed through research history? |journal=PeerJ |date=19 February 2018 |volume=6 |article-number=e4417 |doi=10.7717/peerj.4417|pmid=29479504 |pmc=5822849 |doi-access=free }}</ref><ref name="Howmany">{{cite journal |last1=Starrfelt |first1=Jostein |last2=Liow |first2=Lee Hsiang |title=How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=2016 |volume=371 |issue=1691 |article-number=20150219 |doi=10.1098/rstb.2015.0219|pmid=26977060 |pmc=4810813 }}</ref><ref name="Wang&Dodson"/> and the number that ever existed (in or out of the fossil record) at 3,400.<ref name=russell1995/> A 2016 estimate put the number of dinosaur species living in the Mesozoic at 1,543–2,468,<ref>{{cite journal |last1=Starrfelt |first1=Jostein |last2=Liow |first2=Lee Hsiang |year=2016 |title=How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model |journal=[[Philosophical Transactions of the Royal Society B]] |location=London |publisher=[[Royal Society]] |volume=371 |issue=1691 |article-number=20150219 |doi=10.1098/rstb.2015.0219 |issn=0962-8436 |pmc=4810813 |pmid=26977060}}</ref><ref>{{cite web |url=https://www.nationalgeographic.com/science/article/most-dinosaur-species-are-still-undiscovered/|url-status=live |url-access=registration |last=Black |first=Riley |title=Most Dinosaur Species Are Still Undiscovered |website=[[National Geographic News]] |date=March 23, 2016 |archive-url=https://web.archive.org/web/20210306214843/https://www.nationalgeographic.com/science/article/most-dinosaur-species-are-still-undiscovered/ |archive-date=March 6, 2021 |access-date=June 6, 2021}}</ref>  compared to the number of modern-day birds (avian dinosaurs) at 10,806 species.<ref>{{cite journal|last1=Gill|first1=F.|last2=Donsker|first2=D.|last3=Rasmussen|first3=P.|title=Welcome|year=2021|journal=IOC World Bird List 11.1.|url=https://www.worldbirdnames.org/new/|archive-date=July 30, 2023|access-date=January 25, 2021|archive-url=https://web.archive.org/web/20230730175525/https://www.worldbirdnames.org/new/|url-status=live}}</ref>

Extinct dinosaurs, as well as modern birds, include genera that are herbivorous and others carnivorous, including seed-eaters, fish-eaters, insectivores, and omnivores. While dinosaurs were ancestrally bipedal (as are all modern birds), some evolved into quadrupeds, and others, such as ''[[Anchisaurus]]'' and ''Iguanodon'', could walk as easily on two or four legs. Cranial modifications like horns and crests are common dinosaurian traits, and some extinct species had bony armor. Although the best-known genera are remarkable for their large size, many Mesozoic dinosaurs were human-sized or smaller, and modern birds are generally small in size. Dinosaurs today inhabit every continent, and fossils show that they had achieved global distribution by the [[Early Jurassic]] epoch at latest.<ref name=MacLeod>{{cite journal |last1=MacLeod |first1=Norman |last2=Rawson |first2=Peter F. |last3=Forey |first3=Peter L. |last4=Banner |first4=FT |last5=Boudagher-Fadel |first5=MK |last6=Bown |first6=PR |last7=Burnett |first7=JA |last8=Chambers |first8=P |last9=Culver |first9=S |last10=Evans |first10=SE |last11=Jeffery |first11=C |last12=Kaminski |first12=MA |last13=Lord |first13=AR |last14=Milner |first14=AC |last15=Milner |first15=AR |last16=Morris |first16=N |last17=Owen |first17=E |last18=Rosen |first18=BR |last19=Smith |first19=AB |last20=Taylor |first20=PD |last21=Urquhart |first21=E |last22=Young |first22=JR |display-authors=3 |year=1997 |title=The Cretaceous–Tertiary biotic transition |journal=[[Journal of the Geological Society]] |location=London |publisher=[[Geological Society of London]] |volume=154 |issue=2 |pages=265–292 |doi=10.1144/gsjgs.154.2.0265|bibcode=1997JGSoc.154..265M |s2cid=129654916 |issn=0016-7649}}</ref> Modern birds inhabit most available habitats, from terrestrial to marine, and there is evidence that some non-avian dinosaurs (such as ''[[Microraptor]]'') could fly or at least glide, and others, such as [[spinosauridae|spinosaurids]], had [[semiaquatic]] habits.<ref name=theropods/>

===Distinguishing anatomical features===
While recent discoveries have made it more difficult to present a universally agreed-upon list of their distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton, or are clearly descendants of older dinosaurs showing these modifications. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical for Dinosauria; the earliest dinosaurs had them and passed them on to their descendants. Such modifications, originating in the most recent common ancestor of a certain taxonomic group, are called the [[Synapomorphy and apomorphy|synapomorphies]] of such a group.<ref name="B012"/>
[[File:Dromaeosaurus skull en.svg|thumb|right|Labeled diagram of a typical archosaur skull, the skull of ''[[Dromaeosaurus]]'']]

A detailed assessment of archosaur interrelations by [[Sterling Nesbitt]]<ref name=nesbitt2011/> confirmed or found the following twelve unambiguous synapomorphies, some previously known:
* In the [[skull]], a supratemporal fossa (excavation) is present in front of the [[Skull#Structure|supratemporal fenestra]], the main opening in the rear skull roof
* [[Epipophyses]], obliquely backward-pointing processes on the rear top corners of the anterior (front) neck [[vertebra]]e behind the [[Atlas (anatomy)|atlas]] and [[Axis (anatomy)|axis]], the first two neck vertebrae
* Apex of a deltopectoral crest (a projection on which the [[clavipectoral triangle|deltopectoral]] muscles attach) located at or more than 30% down the length of the [[humerus]] (upper arm bone)
* [[Radius (bone)|Radius]], a lower arm bone, shorter than 80% of humerus length
* [[Fourth trochanter]] (projection where the [[caudofemoralis]] muscle attaches on the inner rear shaft) on the [[femur]] (thigh bone) is a sharp flange
* Fourth trochanter asymmetrical, with distal, lower, margin forming a steeper angle to the shaft
* On the [[Talus bone|astragalus]] and [[Calcaneus|calcaneum]], upper ankle bones, the proximal articular facet, the top connecting surface, for the [[fibula]] occupies less than 30% of the transverse width of the element
* Exoccipitals (bones at the back of the skull) do not meet along the midline on the floor of the endocranial cavity, the inner space of the braincase
* In the pelvis, the proximal articular surfaces of the [[ischium]] with the [[ilium (bone)|ilium]] and the [[Pubis (bone)|pubis]] are separated by a large concave surface (on the upper side of the ischium a part of the open hip joint is located between the contacts with the pubic bone and the ilium)
* [[Cnemial crest]] on the [[tibia]] (protruding part of the top surface of the shinbone) arcs anterolaterally (curves to the front and the outer side)
* Distinct proximodistally oriented (vertical) ridge present on the posterior face of the distal end of the tibia (the rear surface of the lower end of the shinbone)
* Concave articular surface for the fibula of the calcaneum (the top surface of the calcaneum, where it touches the fibula, has a hollow profile)

Nesbitt found a number of further potential synapomorphies and discounted a number of synapomorphies previously suggested. Some of these are also present in [[Silesauridae|silesaurids]], which Nesbitt recovered as a sister group to Dinosauria, including a large anterior trochanter, metatarsals II and IV of subequal length, reduced contact between ischium and pubis, the presence of a cnemial crest on the tibia and of an ascending process on the astragalus, and many others.<ref name=MJB04dino/>

[[File:Sprawling and erect hip joints - horizontal.svg|thumb|Hip joints and hindlimb postures of: (left to right) typical [[reptile]]s (sprawling), dinosaurs and [[mammal]]s (erect), and [[rauisuchia]]ns (pillar-erect)]]

A variety of other skeletal features are shared by dinosaurs. However, because they either are common to other groups of archosaurs or were not present in all early dinosaurs, these features are not synapomorphies. For example, as [[diapsid]]s, dinosaurs ancestrally had two pairs of [[Infratemporal fenestra]]e (openings in the skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the [[antorbital fenestra|snout]] and lower jaw.<ref name=TRHJ00/> Additionally, several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups. These include an elongated [[scapula]], or shoulder blade; a [[sacrum]] composed of three or more fused vertebrae (three are found in some other archosaurs, but only two are found in ''[[Herrerasaurus]]'');<ref name=MJB04dino/> and a perforate [[acetabulum]], or hip socket, with a hole at the center of its inside surface (closed in ''[[Saturnalia tupiniquim]]'', for example).<ref name="UC Berkeley Journal of Earth Sciences">{{cite web |url=https://ucmp.berkeley.edu/diapsids/dinomm.html |last1=Smith |first1=Dave |display-authors=et al. |title=Dinosauria: Morphology |publisher=[[University of California Museum of Paleontology]] |location=Berkeley |access-date=October 16, 2019 |archive-date=November 12, 2020 |archive-url=https://web.archive.org/web/20201112035340/https://ucmp.berkeley.edu/diapsids/dinomm.html |url-status=live }}</ref><ref name=LARB99/> Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the [[Late Triassic]] epoch are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature.<ref name=NIP07/>

Dinosaurs stand with their hind limbs erect in a manner similar to [[Evolution of mammals#Erect limbs|most modern mammals]], but distinct from most other reptiles, whose limbs sprawl out to either side.<ref name=Holland1909/> This posture is due to the development of a laterally facing recess in the pelvis (usually an open socket) and a corresponding inwardly facing distinct head on the femur.<ref name=MJB00/> Their erect posture enabled early dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that [[Carrier's constraint|surpassed those of "sprawling" reptiles]].<ref name=RC05/> Erect limbs probably also helped support the [[evolution]] of large size by reducing bending stresses on limbs.<ref name=TKMB07/> Some non-dinosaurian archosaurs, including [[rauisuchia]]ns, also had erect limbs but achieved this by a "pillar-erect" configuration of the hip joint, where instead of having a projection from the femur insert on a socket on the hip, the [[ilium (bone)|upper pelvic bone]] was rotated to form an overhanging shelf.<ref name=TKMB07/>

==History of study==
{{Further|History of paleontology}}

===Pre-scientific history===
Dinosaur fossils have been known for millennia, although their true nature was not recognized. Chinese authors have long recognised remains of prehistoric animals as "[[dragon bones]]". ''[[Chronicles of Huayang|Huayang Guo Zhi]]''&nbsp;({{zh|t=華陽國志|labels=no}}), a [[gazetteer]] compiled by [[Chang Qu]]&nbsp;({{zh|t=常璩|labels=no}}) during the [[Jin dynasty (266–420)|Western Jin Dynasty]] (265–316), reported the discovery of dragon bones at Wucheng in [[Sichuan]] Province.<ref name=dong1992/> These "dragon bones" were and still are often used as ingredients for remedies in [[Traditional Chinese Medicine]].<ref name="BBCdinobonemed" /> While these "dragon bones" have often popularly been claimed to be dinosaur bones, all known historical examples of vertebrate "dragon bones" from China are actually from [[Cenozoic]] mammals.<ref>{{Cite web |last=Witton |first=Mark |author-link=Mark P. Witton |date=2021-03-26 |title=Mark P. Witton's Blog: Dinosaur fossils and Chinese dragons: ancient association or modern wishful thinking? |url=https://markwitton-com.blogspot.com/2021/03/dinosaur-fossils-and-chinese-dragons.html |access-date=2026-04-12 |website=Mark P. Witton's Blog}}</ref> However, a village in [[Henan]], [[central China]]  was reported in 2007 to have spent the previous several decades excavating and using real dinosaur bones as "dragon bones" for TCM purposes.<ref name="BBCdinobonemed" />  In [[Europe]], dinosaur fossils were generally believed to be the remains of [[giant]]s and other [[Bible|biblical]] creatures.<ref name=benton2000>{{harvnb|Paul|2000|pp=10–44|loc=chpt. 1: "A Brief History of Dinosaur Paleontology" by Michael J. Benton.}}</ref>

===Early dinosaur research===
[[File:William Buckland c1845.jpg|thumb|upright|left|[[William Buckland]]]]

Scholarly descriptions of what would now be recognized as dinosaur bones first appeared in the late 17th century in England. Part of a bone, now known to have been the femur of a ''[[Megalosaurus]]'',<ref name=WAS97/> was recovered from a limestone quarry at [[Cornwell, Oxfordshire|Cornwell]] near [[Chipping Norton]], Oxfordshire, in 1676. The fragment was sent to [[Robert Plot]], Professor of Chemistry at the [[University of Oxford]] and first curator of the [[Ashmolean Museum]], who published a description in his ''The Natural History of Oxford-shire'' (1677).<ref>{{harvnb|Plot|1677|pp=131–139; illus. opp. p. 142, fig. 4}}</ref> He correctly identified the bone as the lower extremity of the femur of a large animal, and recognized that it was too large to belong to any known species. He therefore concluded it to be the femur of a huge human, perhaps a [[Titan (mythology)|Titan]] or another type of giant featured in legends.<ref>{{harvnb|Plot|1677|p=[https://archive.org/details/naturalhistoryo00plot/page/131/mode/1up]}}</ref><ref>{{cite web |url=http://www.oum.ox.ac.uk/learning/pdfs/plot.pdf |title=Robert Plot |author=<!--Staff writer(s); no by-line.--> |year=2006 |website=Learning more |publisher=[[Oxford University Museum of Natural History]] |location=Oxford |archive-url=https://web.archive.org/web/20061001094736/http://www.oum.ox.ac.uk/learning/pdfs/plot.pdf |archive-date=October 1, 2006 |access-date=November 14, 2019}}</ref> [[Edward Lhuyd]], a friend of [[Isaac Newton|Sir Isaac Newton]], published ''Lithophylacii Britannici ichnographia'' (1699), the first scientific treatment of what would now be recognized as a dinosaur. In it he described and named a sauropod [[tooth]], "[[Rutellum|Rutellum impicatum]]",<ref name=L99/><ref name=DS02/> that had been found in Caswell, near [[Witney]], Oxfordshire.<ref name=G45/>

[[File:Dinosaur coining of the word in 1841.jpg|thumb|Sir [[Richard Owen]]'s coining of the word ''dinosaur'', in the 1842 revised version of his talk at an 1841 meeting of the [[British association for the advancement of science|British Association for the Advancement of Science]].]]

Between 1815 and 1824, the Rev [[William Buckland]], the first Reader of Geology at the University of Oxford, collected more fossilized bones of ''Megalosaurus'' and became the first person to describe a non-avian dinosaur in a [[scientific journal]].<ref name=WAS97/><ref name=buckland1824/> The second non-avian dinosaur genus to be identified, ''[[Iguanodon]]'', was purportedly discovered in 1822 by [[Mary Ann Mantell]], the wife of English geologist [[Gideon Mantell]], though this is disputed and some historians say Gideon had acquired remains years earlier. Gideon Mantell recognized similarities between his fossils and the bones of modern [[iguana]]s and published his findings in 1825.<ref name=GM25/><ref name=HDS97/>

The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1842 the English paleontologist Sir Richard Owen coined the term "dinosaur", using it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were then being recognized in England and around the world.<ref name=":2">{{Cite web |date=2017-04-28 |title=The 'birth' of dinosaurs |url=https://morethanadodo.com/2017/04/28/the-birth-of-dinosaurs/ |access-date=2023-03-15 |website=More Than A Dodo |archive-date=March 14, 2023 |archive-url=https://web.archive.org/web/20230314201255/https://morethanadodo.com/2017/04/28/the-birth-of-dinosaurs/ |url-status=live }}</ref><ref name=":3">{{Cite news |date=October 16, 2015 |title=The Birth of Dinosaurs: Richard Owen and Dinosauria |url=https://blog.biodiversitylibrary.org/2015/10/the-birth-of-dinosaurs-richard-owen-and-dinosauria.html |access-date=March 15, 2023 |website=Biodiversity Heritage Library |archive-date=March 14, 2023 |archive-url=https://web.archive.org/web/20230314201310/https://blog.biodiversitylibrary.org/2015/10/the-birth-of-dinosaurs-richard-owen-and-dinosauria.html |url-status=live }}</ref><ref name=":4">{{Cite book |last1=Brett-Surman |first1=M. K. |url=https://books.google.com/books?id=pX_l24sDARwC&dq=Hugh+Torrens+Dinosauria+Owen&pg=PA25 |title=The Complete Dinosaur |last2=Holtz |first2=Thomas R. |last3=Farlow |first3=James O. |date=June 27, 2012 |publisher=Indiana University Press |isbn=978-0-253-00849-7 |page=25 }}</ref><ref name=Owen1841/><ref>{{cite Merriam-Webster|Dinosauria|access-date=November 10, 2019}}</ref> The term is derived {{ety|grc|''[[wikt:δεινός|δεινός]]'' (deinos)|terrible, potent or fearfully great||''[[wikt:σαῦρος|σαῦρος]]'' (sauros)|lizard or reptile}}.<ref name=Owen1841/><ref name=LSJ/> Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it also to evoke their size and majesty.<ref name=FBS97/> Owen recognized that the remains that had been found so far, ''Iguanodon'', ''Megalosaurus'' and ''[[Hylaeosaurus]]'', shared distinctive features, and so decided to present them as a distinct taxonomic group. As clarified by British geologist and historian Hugh Torrens, Owen had given a presentation about fossil reptiles to the British Association for the Advancement of Science in 1841, but reports of the time show that Owen did not mention the word "dinosaur", nor recognize dinosaurs as a distinct group of reptiles in his address. He introduced the Dinosauria only in the revised text version of his talk published in April 1842.<ref name=":2" /><ref name=":3" /> With the backing of [[Prince Albert of Saxe-Coburg and Gotha|Prince Albert]], the husband of [[Queen Victoria]], Owen established the [[Natural History Museum, London]], to display the national collection of dinosaur fossils and other biological and geological exhibits.<ref name=owen94>{{harvnb|Rupke|1994}}</ref>

===Discoveries in North America===
{{multiple image
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| image1            = Edcope.jpg
| caption1          = [[Edward Drinker Cope]]
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| caption2          = [[Othniel Charles Marsh]]
}}

In 1858, [[William Parker Foulke]] discovered the first known American dinosaur in [[marl]] pits in the small town of [[Haddonfield, New Jersey]]. (Although fossils had been found before, their nature had not been correctly discerned.) The creature was named ''[[Hadrosaurus|Hadrosaurus foulkii]]''. It was an extremely important find: ''Hadrosaurus'' was one of the first nearly complete dinosaur skeletons found ([[Iguanodon#Gideon Mantell, Sir Richard Owen, and the discovery of dinosaurs|the first]] was in 1834, in [[Maidstone|Maidstone, England]]), and it was clearly a bipedal creature. This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards. Foulke's discoveries sparked a wave of interests in dinosaurs in the United States, known as Dinosaur Mania.<ref name=weishampel06>{{cite journal |last1=Prieto-Marquez |first1=Albert |last2=Weishampel |first2=David B. |last3=Horner |first3=John R. |date=March 2006 |title=The dinosaur ''Hadrosaurus foulkii'', from the Campanian of the East Coast of North America, with a reevaluation of the genus |url=https://app.pan.pl/archive/published/app51/app51-077.pdf |url-status=live |journal=Acta Palaeontologica Polonica |location=Warsaw |publisher=Institute of Paleobiology, Polish Academy of Sciences |volume=51 |issue=1 |pages=77–98 |issn=0567-7920 |archive-url=https://web.archive.org/web/20190622113255/https://app.pan.pl/archive/published/app51/app51-077.pdf |archive-date=June 22, 2019 |access-date=November 5, 2019}}</ref>

Dinosaur mania was exemplified by the fierce rivalry between [[Edward Drinker Cope]] and [[Othniel Charles Marsh]], both of whom raced to be the first to find new dinosaurs in what came to be known as the [[Bone Wars]]. This fight between the two scientists lasted for over 30 years, ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt. Many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods: for example, their diggers often used [[dynamite]] to unearth bones. Modern paleontologists would find such methods crude and unacceptable, since blasting easily destroys fossil and stratigraphic evidence. Despite their unrefined methods, the contributions of Cope and Marsh to paleontology were vast: Marsh unearthed 86 new species of dinosaur and Cope discovered 56, a total of 142 new species. Cope's collection is now at the [[American Museum of Natural History]] in New York City, while Marsh's is at the [[Peabody Museum of Natural History]] at [[Yale University]].<ref name=Holmes/>

==="Dinosaur renaissance" and beyond===
{{Main|Dinosaur renaissance}}

[[World War II]] caused a pause in palaeontological research; after the war, research attention was also diverted increasingly to fossil mammals rather than dinosaurs, which were seen as sluggish and cold-blooded.<ref name="taylor2010">{{cite journal |last1=Taylor |first1=M.P. |title=Sauropod dinosaur research: a historical review |journal=Geological Society, London, Special Publications |year=2010 |volume=343 |issue=1 |pages=361–386 |doi=10.1144/SP343.22|bibcode=2010GSLSP.343..361T |s2cid=910635 }}</ref><ref name="Naish">{{cite book |last=Naish |first=D. |year=2009 |title=The Great Dinosaur Discoveries |pages=89–93 |publisher=A & C Black Publishers Ltd. |location=London, UK |isbn=978-1-4081-1906-8}}</ref> At the end of the 1960s, however, the field of dinosaur research experienced a surge in activity that remains ongoing.<ref name="arbour2018">{{cite journal |last1=Arbour |first1=V. |year=2018 |title=Results roll in from the dinosaur renaissance |journal=Science |volume=360 |issue=6389 |page=611 |doi=10.1126/science.aat0451|bibcode=2018Sci...360..611A |s2cid=46887409 }}</ref> Several seminal studies led to this activity. First, [[John Ostrom]] discovered the bird-like [[dromaeosauridae|dromaeosaurid]] theropod ''[[Deinonychus]]'' and described it in 1969. Its anatomy indicated that it was an active predator that was likely warm-blooded, in marked contrast to the then-prevailing image of dinosaurs.<ref name="taylor2010"/> Concurrently, [[Robert T. Bakker]] published a series of studies that likewise argued for active lifestyles in dinosaurs based on anatomical and ecological evidence (see {{section link||Physiology}}),<ref name="bakker1968"/><ref name="bakker1972"/> which were subsequently summarized in his 1986 book ''[[The Dinosaur Heresies]]''.<ref name=bakker86>{{harvnb|Bakker|1986}}</ref>

[[File:Dr. Bob Bakker with Dino.jpg|thumb|left|Paleontologist [[Robert T. Bakker]] with a mounted skeleton of a [[Tyrannosauridae|tyrannosaurid]] (''[[Gorgosaurus|Gorgosaurus libratus]]'')]]
New revelations were supported by an increase in dinosaur discoveries. Major new dinosaur discoveries have been made by paleontologists working in previously unexplored regions, including India, South America, Madagascar, Antarctica, and most significantly China. Across theropods, sauropodomorphs, and ornithischians, the number of named genera began to increase drastically in the 1990s,<ref name="Genera900"/> with up to 30 new species of dinosaurs named each year by 2008.<ref name="benton2008"/> At least sauropodomorphs experienced a further increase in the number of named species in the 2010s, with an average of 9.3 new species having been named each year between 2009 and 2020. As a consequence, more sauropodomorphs were named between 1990 and 2020 than in all previous years combined.<ref name="cashmore2020">{{cite journal |last1=Cashmore |first1=D.D. |last2=Mannion |first2=P.D. |last3=Upchurch |first3=P. |last4=Butler |first4=R.J. |year=2020 |title=Ten more years of discovery: revisiting the quality of the sauropodomorph dinosaur fossil record |journal=Palaeontology |volume=63 |issue=6 |pages=951–978 |doi=10.1111/pala.12496|bibcode=2020Palgy..63..951C |s2cid=219090716 |doi-access=free }}</ref> These new localities also led to improvements in overall specimen quality, with new species being increasingly named not on scrappy fossils but on more complete skeletons, sometimes from multiple individuals. Better specimens also led to new species being invalidated less frequently.<ref name="benton2008">{{cite journal |last1=Benton |first1=M.J. |year=2008 |title=Fossil quality and naming dinosaurs |journal=Biology Letters |volume=4 |issue=6 |pages=729–732 |doi=10.1098/rsbl.2008.0402|pmid=18796391 |pmc=2614166 |bibcode=2008BiLet...4..729B }}</ref> Asian localities have produced the most complete theropod specimens,<ref name="cashmore2019">{{cite journal |last1=Cashmore |first1=D.D. |last2=Butler |first2=R.J. |year=2019 |title=Skeletal completeness of the non-avian theropod dinosaur fossil record |journal=Palaeontology |volume=62 |issue=6 |pages=951–981 |doi=10.1111/pala.12436|s2cid=197571209 |doi-access=free |bibcode=2019Palgy..62..951C }}</ref> while North American localities have produced the most complete sauropodomorph specimens.<ref name="cashmore2020"/>

Prior to the dinosaur renaissance, dinosaurs were mostly classified using the traditional rank-based system of [[Linnaean taxonomy]]. The renaissance was also accompanied by the increasingly widespread application of [[cladistics]], a more objective method of classification based on ancestry and shared traits, which has proved tremendously useful in the study of dinosaur systematics and evolution. Cladistic analysis, among other techniques, helps to compensate for an often incomplete and fragmentary fossil record.<ref name="holtz1997">{{cite book |last1=Holtz |first1=T.R. Jr. |last2=Brett-Surman |first2=M.K. |year=1997 |chapter=The Taxonomy and Systematics of Dinosaurs |title=The Complete Dinosaur |publisher=Indiana University Press |location=Bloomington |pages=209–223 |isbn=978-0-253-33349-0 |chapter-url=https://books.google.com/books?id=Hk5ecvEv0GcC&pg=PA209}}</ref><ref name="NYT-20161208">{{cite news |last=St. Fleur |first=Nicholas |title=That Thing With Feathers Trapped in Amber? It Was a Dinosaur Tail |url=https://www.nytimes.com/2016/12/08/science/dinosaur-feathers-amber.html |url-status=live |url-access=registration |date=December 8, 2016 |department=Trilobites |work=The New York Times |location=New York |issn=0362-4331 |archive-url=https://web.archive.org/web/20170831181949/https://www.nytimes.com/2016/12/08/science/dinosaur-feathers-amber.html |archive-date=August 31, 2017 |access-date=December 8, 2016}}</ref> Reference books summarizing the state of dinosaur research, such as [[David B. Weishampel]] and colleagues' ''[[The Dinosauria]]'', made knowledge more accessible<ref name="lockley2000">{{cite journal |last1=Lockley |first1=M.G. |last2=Wright |first2=J.L. |year=2000 |title=Reading About Dinosaurs – An Annotated Bibliography of Books |journal=Journal of Geoscience Education |volume=48 |issue=2 |pages=167–178 |doi=10.5408/1089-9995-48.2.167|bibcode=2000JGeEd..48..167L |s2cid=151426669 }}</ref> and spurred further interest in dinosaur research. The release of the first and second editions of ''The Dinosauria'' in 1990 and 2004, and of a review paper by [[Paul Sereno]] in 1998, were accompanied by increases in the number of published [[phylogenetic tree]]s for dinosaurs.<ref name="lloyd2008">{{cite journal |last1=Lloyd |first1=G.T. |last2=Davis |first2=K.E. |last3=Pisani |first3=D. |last4=Tarver |first4=J.E. |last5=Ruta |first5=R. |last6=Sakamoto |first6=M. |last7=Hone |first7=D.W.E. |last8=Jennings |first8=R. |last9=Benton |first9=M.J. |year=2008 |title=Dinosaurs and the Cretaceous Terrestrial Revolution |journal=Proceedings of the Royal Society B |volume=275 |issue=1650 |pages=2483–2490 |doi=10.1098/rspb.2008.0715|pmid=18647715 |pmc=2603200 }}</ref>

===Soft tissue and molecular preservation===
[[File:Dakota skin impression.jpg|thumb|An ''[[Edmontosaurus]]'' specimen's skin impressions found in 1999]]

Dinosaur fossils are not limited to bones, but also include imprints or mineralized remains of skin coverings, organs, and other tissues. Of these, skin coverings based on [[keratin]] proteins are most easily preserved because of their [[cross-link]]ed, [[hydrophobe|hydrophobic]] molecular structure.<ref name="schweitzer2011">{{cite journal |last1=Schweitzer |first1=M.H. |year=2011 |title=Soft Tissue Preservation in Terrestrial Mesozoic Vertebrates |journal=Annual Review of Earth and Planetary Sciences |volume=39 |pages=187–216 |doi=10.1146/annurev-earth-040610-133502|bibcode=2011AREPS..39..187S }}</ref> Fossils of keratin-based skin coverings or bony skin coverings are known from most major groups of dinosaurs. Dinosaur fossils with scaly skin impressions have been found since the 19th century. [[Samuel Beckles]] discovered a sauropod forelimb with preserved skin in 1852 that was incorrectly attributed to a crocodile; it was correctly attributed by Marsh in 1888 and subject to further study by [[Reginald Hooley]] in 1917.<ref name="hooley1917"/> Among ornithischians, in 1884 Jacob Wortman found skin impressions on the first known specimen of ''[[Edmontosaurus annectens]]'', which were largely destroyed during the specimen's excavation.<ref name="osborn1912">{{cite journal |first1=H.F. |last1=Osborn |year=1912 |title=Integument of the iguanodont dinosaur ''Trachodon'' |journal=Memoirs of the American Museum of Natural History |volume=1 |pages=33–54}}</ref> Owen and Hooley subsequently described skin impressions of ''[[Hypsilophodon]]'' and ''Iguanodon'' in 1885 and 1917.<ref name="hooley1917">{{cite journal |last1=Hooley |first1=R.W. |year=1917 |title=II—On the Integument of ''Iguanodon bernissartensis'', Boulenger, and of ''Morosaurus becklesii'', Mantell |journal=Geological Magazine |volume=4 |issue=4 |pages=148–150 |doi=10.1017/s0016756800192386 |bibcode=1917GeoM....4..148H |s2cid=129640665 |url=https://zenodo.org/record/1537494 |archive-date=April 15, 2023 |access-date=February 20, 2023 |archive-url=https://web.archive.org/web/20230415133707/https://zenodo.org/record/1537494 |url-status=live }}</ref> Since then, scale impressions have been most frequently found among hadrosaurids, where the impressions are known from nearly the entire body across multiple specimens.<ref name="bell2014">{{cite book |last1=Bell |first1=P.R. |year=2014 |chapter=A review of hadrosaur skin impressions |editor-last1=Eberth |editor-first1=D. |editor-last2=Evans |editor-first2=D. |title=The Hadrosaurs: Proceedings of the International Hadrosaur Symposium |pages=572–590 |location=Bloomington |publisher=Princeton University Press}}</ref>

{{multiple image
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| caption_align     = center
| image1            = Sinosauropteryx color.jpg
| caption1          = Color restoration of ''[[Sinosauropteryx]]''
| image2            = Psittacosaurus (Vinther et al. 2016, cropped).png
| caption2          = Color restoration of ''[[Psittacosaurus]]''
}}

Starting from the 1990s, major discoveries of exceptionally preserved fossils in deposits known as conservation [[Lagerstätte]]n contributed to research on dinosaur soft tissues.<ref name="eliason2017">{{cite journal |last1=Eliason |first1=C.M. |last2=Hudson |first2=L. |last3=Watts |first3=T. |last4=Garza |first4=H. |last5=Clarke |first5=J.A. |year=2017 |title=Exceptional preservation and the fossil record of tetrapod integument |journal=Proceedings of the Royal Society B |volume=284 |issue=1862 |pages=1–10 |doi=10.1098/rspb.2017.0556|pmid=28878057 |pmc=5597822 }}</ref><ref name="benton1998">{{cite journal |last1=Benton |first1=M.J. |year=1998 |title=Dinosaur fossils with soft parts |journal=Trends in Ecology & Evolution |volume=13 |issue=8 |pages=303–304 |doi=10.1016/s0169-5347(98)01420-7|pmid=21238317 |bibcode=1998TEcoE..13..303B |url=http://doc.rero.ch/record/14715/files/PAL_E1646.pdf }}</ref> Chiefly among these were the rocks that produced the [[Jehol Biota|Jehol]] (Early Cretaceous) and [[Yanliao Biota|Yanliao]] (Mid-to-Late Jurassic) [[biota (ecology)|biota]]s of northeastern China, from which hundreds of dinosaur specimens bearing impressions of feather-like structures (both closely related to birds and otherwise, see {{section link||Origin of birds}}) have been described by [[Xu Xing (paleontologist)|Xing Xu]] and colleagues.<ref name="zhou2017">{{cite journal |last1=Zhou |first1=Z.-H. |last2=Wang |first2=Y. |year=2017 |title=Vertebrate assemblages of the Jurassic Yanliao Biota and the Early Cretaceous Jehol Biota: Comparisons and implications |journal=Palaeoworld |volume=26 |issue=2 |pages=241–252 |doi=10.1016/j.palwor.2017.01.002 |bibcode=2017Palae..26..241Z }}</ref><ref name="norell2005">{{cite journal |last1=Norell |first1=M.A. |last2=Xu |first2=X. |year=2005 |title=Feathered Dinosaurs |journal=Annual Review of Earth and Planetary Sciences |volume=33 |pages=277–299 |doi=10.1146/annurev.earth.33.092203.122511|bibcode=2005AREPS..33..277N }}</ref> In living reptiles and mammals, pigment-storing cellular structures known as [[melanosome]]s are partially responsible for producing colouration.<ref name="roy2020"/><ref name="vinther2020">{{cite journal |last1=Vinther |first1=J. |year=2020 |title=Reconstructing Vertebrate Paleocolor |journal=Annual Review of Earth and Planetary Sciences |volume=48 |pages=345–375 |doi=10.1146/annurev-earth-073019-045641|bibcode=2020AREPS..48..345V |s2cid=219768255 |doi-access=free }}</ref> Both chemical traces of [[melanin]] and characteristically shaped melanosomes have been reported from feathers and scales of Jehol and Yanliao dinosaurs, including both theropods and ornithischians.<ref name="zhang2010">{{cite journal |last1=Zhang |first1=F. |last2=Kearns |first2=S.L. |last3=Orr |first3=P.J. |last4=Benton |first4=M.J. |last5=Zhou |first5=Z. |last6=Johnson |first6=D. |last7=Xu |first7=X. |last8=Wang |first8=X. |year=2010 |title=Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds |journal=Nature |volume=463 |issue=7284 |pages=1075–1078 |doi=10.1038/nature08740 |pmid=20107440 |bibcode=2010Natur.463.1075Z |s2cid=205219587 |url=http://oro.open.ac.uk/22432/2/41064696.pdf |archive-date=February 2, 2014 |access-date=February 20, 2023 |archive-url=https://web.archive.org/web/20140202214645/http://oro.open.ac.uk/22432/2/41064696.pdf |url-status=live }}</ref> This has enabled multiple full-body reconstructions of [[dinosaur colouration]], such as for ''[[Sinosauropteryx]]''<ref name="smithwick2017">{{cite journal |last1=Smithwick |first1=F.M. |last2=Nicholls |first2=R. |last3=Cuthill |first3=I.C. |last4=Vinther |first4=J. |year=2017 |title=Countershading and Stripes in the Theropod Dinosaur ''Sinosauropteryx'' Reveal Heterogeneous Habitats in the Early Cretaceous Jehol Biota |journal=Current Biology |volume=27 |issue=21 |pages=3337–3343.e2 |doi=10.1016/j.cub.2017.09.032 |pmid=29107548 |doi-access=free|bibcode=2017CBio...27E3337S |hdl=1983/8ee95b15-5793-42ad-8e57-da6524635349 |hdl-access=free }}</ref> and ''[[Psittacosaurus]]''<ref name="vinther2016">{{cite journal |last1=Vinther |first1=J. |last2=Nicholls |first2=R. |last3=Lautenschlager |first3=S. |last4=Pittman |first4=M. |last5=Kaye |first5=T.G. |last6=Rayfield |first6=E. |last7=Mayr |first7=G. |last8=Cuthill |first8=I.C. |year=2016 |title=3D Camouflage in an Ornithischian Dinosaur |journal=Current Biology |volume=26 |issue=18 |pages=2456–2462 |doi=10.1016/j.cub.2016.06.065 |pmid=27641767 |pmc=5049543|bibcode=2016CBio...26.2456V }}</ref> by Jakob Vinther and colleagues, and similar techniques have also been extended to dinosaur fossils from other localities.<ref name="roy2020">{{cite journal |last1=Roy |first1=A. |last2=Pittman |first2=M. |last3=Saitta |first3=E.T. |last4=Kaye |first4=T.G. |last5=Xu |first5=X. |year=2020 |title=Recent advances in amniote palaeocolour reconstruction and a framework for future research |journal=Biological Reviews |volume=95 |issue=1 |pages=22–50 |doi=10.1111/brv.12552|pmid=31538399 |pmc=7004074 }}</ref> (However, some researchers have also suggested that fossilized melanosomes represent bacterial remains.<ref name="lindgren2015">{{cite journal |last1=Lindgren |first1=J. |last2=Moyer |first2=A. |last3=Schweitzer |first3=M.H. |last4=Sjövall |first4=P. |last5=Uvdal |first5=P. |last6=Nilsson |first6=D.E. |last7=Heimdal |first7=J. |last8=Engdahl |first8=A. |last9=Gren |first9=J.A. |last10=Schultz |first10=B.P. |last11=Kear |first11=B.P. |year=2015 |title=Interpreting melanin-based coloration through deep time: a critical review |journal=Proceedings of the Royal Society B |volume=282 |issue=1813 |article-number=20150614 |pmid=26290071 |doi=10.1098/rspb.2015.0614 |pmc=4632609 |bibcode=2015PBioS.28250614L }}</ref><ref name="schweitzer2015">{{cite journal |last1=Schweitzer |first1=M.H. |last2=Lindgren |first2=J. |last3=Moyer |first3=A.E. |year=2015 |title=Melanosomes and ancient coloration re-examined: a response to Vinther 2015 (DOI 10.1002/bies.201500018) |journal=BioEssays |volume=37 |issue=11 |pages=1174–1183 |doi=10.1002/bies.201500061|pmid=26434749 |s2cid=45178498 }}</ref>) Stomach contents in some Jehol and Yanliao dinosaurs closely related to birds have also provided indirect indications of diet and digestive system anatomy (e.g., [[crop (anatomy)|crops]]).<ref name="zhou2014">{{cite journal |last1=Zhou |first1=Z. |year=2014 |title=The Jehol Biota, an Early Cretaceous terrestrial Lagerstätte: new discoveries and implications |journal=National Science Review |volume=1 |issue=4 |pages=543–559 |doi=10.1093/nsr/nwu055|doi-access=free }}</ref><ref name="oconnor2019">{{cite journal |last1=O'Connor |first1=J.K. |last2=Zhou |first2=Z. |year=2019 |title=The evolution of the modern avian digestive system: insights from paravian fossils from the Yanliao and Jehol biotas |journal=Palaeontology |volume=63 |issue=1 |pages=13–27 |doi=10.1111/pala.12453|s2cid=210265348 }}</ref> More concrete evidence of internal anatomy has been reported in ''[[Scipionyx]]'' from the [[Pietraroja Plattenkalk]] of Italy. It preserves portions of the intestines, colon, liver, muscles, and windpipe.<ref name="softtissue"/>

[[File:9121 - Milano, Museo storia naturale - Scipionyx samniticus - Foto Giovanni Dall'Orto 22-Apr-2007a.jpg|thumb|''[[Scipionyx]]'' fossil with intestines, [[Museo Civico di Storia Naturale di Milano|Natural History Museum of Milan]]]]
Concurrently, a line of work led by [[Mary Higby Schweitzer]], [[Jack Horner (paleontologist)|Jack Horner]], and colleagues reported various occurrences of preserved soft tissues and proteins within dinosaur bone fossils. Various mineralized structures that likely represented [[red blood cell]]s and [[collagen]] fibres had been found by Schweitzer and others in [[tyrannosauridae|tyrannosaurid]] bones as early as 1991.<ref name="morell1993">{{cite journal |last1=Morell |first1=V. |year=1993 |title=Dino DNA: the Hunt and the Hype |journal=Science |volume=261 |issue=5118 |pages=160–162 |doi=10.1126/science.8327889|pmid=8327889 |bibcode=1993Sci...261..160M }}</ref><ref name="pawlicki1996">{{cite journal |last1=Pawlicki |first1=R. |last2=Korbel |first2=A. |last3=Kubiak |first3=H. |year=1996 |title=Cells, Collagen Fibrils and Vessels in Dinosaur Bone |journal=Nature |volume=211 |issue=5049 |pages=655–657 |doi=10.1038/211655a0|pmid=5968744 |s2cid=4181847 }}</ref><ref name="pawlicki1998">{{cite journal |last1=Pawlicki |first1=R. |last2=Nowogrodzka-Zagórska |first2=M. |year=1998 |title=Blood vessels and red blood cells preserved in dinosaur bones |journal=Annals of Anatomy - Anatomischer Anzeiger |volume=180 |issue=1 |pages=73–77 |doi=10.1016/S0940-9602(98)80140-4|pmid=9488909 }}</ref> However, in 2005, Schweitzer and colleagues reported that a femur of ''[[Tyrannosaurus]]'' preserved soft, flexible tissue within, including [[blood vessel]]s, [[osteon|bone matrix]], and connective tissue (bone fibers) that had retained their microscopic structure.<ref name=Schweitzer2005/> This discovery suggested that original soft tissues could be preserved over geological time,<ref name="schweitzer2011"/> with multiple mechanisms having been proposed.<ref name="anderson2023">{{cite journal |last1=Anderson |first1=L.A. |year=2023 |title=A chemical framework for the preservation of fossil vertebrate cells and soft tissues |journal=Earth-Science Reviews |volume=240 |article-number=104367 |doi=10.1016/j.earscirev.2023.104367|bibcode=2023ESRv..24004367A |s2cid=257326012 |doi-access=free }}</ref> Later, in 2009, Schweitzer and colleagues reported that a ''[[Brachylophosaurus]]'' femur preserved similar microstructures, and [[immunohistochemistry|immunohistochemical]] techniques (based on [[antibody]] binding) demonstrated the presence of proteins such as collagen, [[elastin]], and [[laminin]].<ref name="schweitzer2009">{{cite journal |last1=Schweitzer |first1=M.H. |last2=Zheng |first2=W. |last3=Organ |first3=C.L. |last4=Avci |first4=R. |last5=Suo |first5=Z. |last6=Freimark |first6=L.M. |last7=LeBleu |first7=V.S. |last8=Duncan |first8=M.B. |last9=van der Heiden |first9=M.G. |last10=Neveu |first10=J.M. |last11=Lane |first11=W.S. |last12=Cottrell |first12=J.S. |last13=Horner |first13=J.R. |last14=Cantley |first14=L.C. |last15=Kalluri |first15=R. |last16=Asara |first16=J.M. |year=2009 |title=Biomolecular characterization and protein sequences of the Campanian hadrosaur ''B. canadensis'' |journal=Science |volume=324 |issue=5927 |pages=626–631 |doi=10.1126/science.1165069|pmid=19407199 |bibcode=2009Sci...324..626S |s2cid=5358680 }}</ref> Both specimens yielded collagen protein sequences that were viable for [[molecular phylogenetics|molecular phylogenetic analyses]], which grouped them with birds as would be expected.<ref name="schweitzer2009"/><ref name="organ2008">{{cite journal |last1=Organ |first1=C.L. |last2=Schweitzer |first2=M.H. |last3=Zheng |first3=W. |last4=Freimark |first4=L.M. |last5=Cantley |first5=L.C. |last6=Asara |first6=J.M. |year=2008 |title=Molecular Phylogenetics of Mastodon and ''Tyrannosaurus rex'' |journal=Science |volume=320 |issue=5875 |page=499 |doi=10.1126/science.1154284|pmid=18436782 |bibcode=2008Sci...320..499O |s2cid=24971064 }}</ref> The extraction of fragmentary DNA has also been reported for both of these fossils,<ref name="schweitzer2013">{{cite journal |last1=Schweitzer |first1=M.H. |last2=Zheng |first2=W. |last3=Cleland |first3=T.P. |last4=Bern |first4=M. |year=2013 |title=Molecular analyses of dinosaur osteocytes support the presence of endogenous molecules |journal=[[Bone (journal)|Bone]] |location=Amsterdam |publisher=Elsevier |volume=52 |issue=1 |pages=414–423 |doi=10.1016/j.bone.2012.10.010 |issn=8756-3282 |pmid=23085295}}</ref> along with a specimen of ''[[Hypacrosaurus]]''.<ref name="bailleul2020">{{cite journal |last1=Bailleul |first1=A.M. |last2=Zheng |first2=W. |last3=Horner |first3=J.R. |last4=Hall |first4=B.K. |last5=Holliday |first5=C.M. |last6=Schweitzer |first6=M.H. |year=2020 |title=Evidence of proteins, chromosomes and chemical markers of DNA in exceptionally preserved dinosaur cartilage |journal=National Science Review |volume=7 |issue=4 |pages=815–822 |doi=10.1093/nsr/nwz206|pmid=34692099 |pmc=8289162 }}</ref> In 2015, Sergio Bertazzo and colleagues reported the preservation of collagen fibres and red blood cells in eight Cretaceous dinosaur specimens that did not show any signs of exceptional preservation, indicating that soft tissue may be preserved more commonly than previously thought.<ref name="bertazzo2015">{{cite journal |last1=Bertazzo |first1=S. |last2=Maidment |first2=S.C.R. |author2-link=Susannah Maidment |last3=Kallepitis |first3=C. |last4=Fearn |first4=S. |last5=Stevens |first5=M.M. |last6=Xie |first6=H.-N. |display-authors=3 |year=2015 |title=Fibres and cellular structures preserved in 75-million-year-old dinosaur specimens |journal=[[Nature Communications]] |volume=6 |article-number=7352 |bibcode=2015NatCo...6.7352B |doi=10.1038/ncomms8352 |issn=2041-1723 |pmc=4468865 |pmid=26056764}}</ref> Suggestions that these structures represent bacterial [[biofilm]]s<ref name="kaye2008">{{cite journal |last1=Kaye |first1=T.G. |last2=Gaugler |first2=G. |last3=Sawlowicz |first3=Z. |year=2008 |title=Dinosaurian Soft Tissues Interpreted as Bacterial Biofilms |journal=PLOS ONE |volume=3 |issue=7 |article-number=e2808 |doi=10.1371/journal.pone.0002808|pmid=18665236 |pmc=2483347 |bibcode=2008PLoSO...3.2808K |doi-access=free }}</ref> have been rejected,<ref name="peterson2010">{{cite journal |last1=Peterson |first1=J.E. |last2=Lenczewski |first2=M.E. |last3=Scherer |first3=R.P. |year=2010 |title=Influence of Microbial Biofilms on the Preservation of Primary Soft Tissue in Fossil and Extant Archosaurs |journal=PLOS ONE |volume=5 |issue=10 |article-number=e13334 |bibcode=2010PLoSO...513334P |doi=10.1371/journal.pone.0013334 |doi-access=free |issn=1932-6203 |pmc=2953520 |pmid=20967227}}</ref> but cross-contamination remains a possibility that is difficult to detect.<ref name="buckley2017">{{cite journal |last1=Buckley |first1=M. |last2=Warwood |first2=S. |last3=van Dongen |first3=B. |last4=Kitchener |first4=A.C. |last5=Manning |first5=P.L. |year=2017 |title=A fossil protein chimera; difficulties in discriminating dinosaur peptide sequences from modern cross-contamination |journal=Proceedings of the Royal Society B |volume=284 |issue=1855 |doi=10.1098/rspb.2017.0544|pmid=28566488 |pmc=5454271 |bibcode=2017PBioS.28470544B }}</ref>

==Evolutionary history==
===Origins and early evolution===
[[File:Herrerasaurusskeleton.jpg|thumb|alt=Full skeleton of an early carnivorous dinosaur, displayed in a glass case in a museum|The early dinosaurs ''[[Herrerasaurus]]'' (large), ''[[Eoraptor]]'' (small) and a ''[[Plateosaurus]]'' skull, from the [[Triassic]]]]
Dinosaurs diverged from their archosaur ancestors during the Middle to Late Triassic epochs, roughly 20&nbsp;million years after the devastating [[Permian–Triassic extinction event]] wiped out an estimated 96% of all marine species and 70% of terrestrial vertebrate species approximately 252&nbsp;million years ago.<ref name=KPA/><ref name=TannerLucas/> The oldest dinosaur fossils known from substantial remains date to the [[Carnian]] epoch of the Triassic period and have been found primarily in the [[Ischigualasto Formation|Ischigualasto]] and [[Santa Maria Formation]]s of Argentina and Brazil, and the [[Pebbly Arkose Formation]] of Zimbabwe.<ref name="griffin2022">{{cite journal |last1=Griffin |first1=C.T. |last2=Wynd |first2=B.M. |last3=Munyikwa |first3=D. |last4=Broderick |first4=T.J. |last5=Zondo |first5=M. |last6=Tolan |first6=S. |last7=Langer |first7=M.C. |last8=Nesbitt |first8=S.J. |last9=Taruvinga |first9=H.R. |year=2022 |title=Africa's oldest dinosaurs reveal early suppression of dinosaur distribution |journal=Nature |volume=609 |issue=7926 |pages=313–319 |doi=10.1038/s41586-022-05133-x |pmid=36045297 |bibcode=2022Natur.609..313G |s2cid=251977824 |issn=0028-0836}}</ref>

The Ischigualasto Formation ([[radiometric dating|radiometrically dated]] at 231–230&nbsp;million years old<ref name="desojo2020">{{cite journal |last1=Desojo |first1=J.B. |last2=Fiorelli |first2=L.E. |last3=Ezcurra |first3=M.D. |last4=Martinelli |first4=A.G. |last5=Ramezani |first5=J. |last6=Da Rosa |first6=A.A.S. |last7=Belén von Baczko |first7=M. |last8=Jimena Trotteyn |first8=M. |last9=Montefeltro |first9=F.C. |last10=Ezpeleta |first10=M. |last11=Langer |first11=M.C. |year=2020 |title=The Late Triassic Ischigualasto Formation at Cerro Las Lajas (La Rioja, Argentina): fossil tetrapods, high-resolution chronostratigraphy, and faunal correlations |journal=Scientific Reports |volume=10 |issue=1 |page=12782 |doi=10.1038/s41598-020-67854-1 |pmid=32728077 |pmc=7391656 |bibcode=2020NatSR..1012782D}}</ref>) has produced the early saurischian ''[[Eoraptor]]'', originally considered a member of the [[Herrerasauridae]]<ref name="OARM2010">{{cite journal |last1=Alcober |first1=Oscar A. |last2=Martinez |first2=Ricardo N. |year=2010 |title=A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina |journal=[[ZooKeys]] |location=[[Sofia]] |publisher=[[Pensoft Publishers]] |issue=63 |pages=55–81 |doi=10.3897/zookeys.63.550 |pmc=3088398 |issn=1313-2989 |pmid=21594020|bibcode=2010ZooK...63...55A |doi-access=free}}</ref> but now considered to be an early sauropodomorph, along with the herrerasaurids ''Herrerasaurus'' and ''[[Sanjuansaurus]]'', and the sauropodomorphs ''[[Chromogisaurus]]'', ''[[Eodromaeus]]'', and ''[[Panphagia]]''.<ref name="novas2021">{{cite journal |last1=Novas |first1=F.E. |last2=Agnolin |first2=F.L. |last3=Ezcurra |first3=M.D. |last4=Müller |first4=R.T. |last5=Martinelli |first5=A. |last6=Langer |first6=M. |year=2021 |title=Review of the fossil record of early dinosaurs from South America, and its phylogenetic implications |journal=Journal of South American Earth Sciences |volume=110 |article-number=103341 |doi=10.1016/j.jsames.2021.103341 |issn=0895-9811 |bibcode=2021JSAES.11003341N}}</ref> ''Eoraptor''{{'s}} likely resemblance to the [[Common descent|common ancestor]] of all dinosaurs suggests that the first dinosaurs would have been small, bipedal [[predation|predators]].<ref name="Daemonosaurus">{{cite journal |last1=Nesbitt |first1=Sterling J |last2=Sues |first2=Hans-Dieter |title=The osteology of the early-diverging dinosaur ''Daemonosaurus chauliodus'' (Archosauria: Dinosauria) from the Coelophysis Quarry (Triassic: Rhaetian) of New Mexico and its relationships to other early dinosaurs |journal=Zoological Journal of the Linnean Society |date=2021 |volume=191 |issue=1 |pages=150–179 |doi=10.1093/zoolinnean/zlaa080|doi-access=free }}</ref><ref name=Sereno1999/><ref name=SFRM93/> The Santa Maria Formation (radiometrically dated to be older, at 233.23&nbsp;million years old<ref name=langer18>{{cite journal |last1=Langer |first1=Max C.|last2=Ramezani |first2=Jahandar |last3=Da Rosa |first3=Átila A.S. |title=U-Pb age constraints on dinosaur rise from south Brazil |date=May 2018 |journal=[[Gondwana Research]] |location=Amsterdam |publisher=Elsevier |volume=57 |pages=133–140 |doi=10.1016/j.gr.2018.01.005 |bibcode=2018GondR..57..133L |issn=1342-937X}}</ref>) has produced the herrerasaurids ''[[Gnathovorax]]'' and ''[[Staurikosaurus]]'', along with the sauropodomorphs ''[[Bagualosaurus]]'', ''[[Buriolestes]]'', ''[[Guaibasaurus]]'', ''[[Macrocollum]]'', ''[[Nhandumirim]]'', ''[[Pampadromaeus]]'', ''Saturnalia'', and ''[[Unaysaurus]]''.<ref name="novas2021"/> The Pebbly Arkose Formation, which is of uncertain age but was likely comparable to the other two, has produced the sauropodomorph ''[[Mbiresaurus]]'', along with an unnamed herrerasaurid.<ref name="griffin2022"/>

Less well-preserved remains of the sauropodomorphs ''[[Jaklapallisaurus]]'' and ''[[Nambalia]]'', along with the early saurischian ''[[Alwalkeria]]'', are known from the [[Upper Maleri Formation|Upper Maleri]] and [[Lower Maleri Formation]]s of India.<ref name="novas2011">{{cite journal |last1=Novas |first1=F.E. |last2=Ezcurra |first2=M.D. |last3=Chatterjee |first3=S. |last4=Kutty |first4=T.S. |year=2011 |title=New dinosaur species from the Upper Triassic Upper Maleri and Lower Dharmaram formations of central India |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |volume=101 |issue=3–4 |pages=333–349 |doi=10.1017/S1755691011020093|bibcode=2010EESTR.101..333N |s2cid=128620874 }}</ref> The Carnian-aged [[Chañares Formation]] of Argentina preserves primitive, dinosaur-like ornithodirans such as ''[[Lagosuchus]]'' and ''[[Lagerpeton]]'' in [[Argentina]], making it another important site for understanding dinosaur evolution. These ornithodirans support the model of early dinosaurs as small, bipedal predators.<ref name="novas2021"/><ref name="mariscano2016">{{cite journal |last1=Marsicano |first1=C.A. |last2=Irmis |first2=R.B. |last3=Mancuso |first3=A.C. |last4=Mundil |first4=R. |last5=Chemale |first5=F. |year=2016 |title=The precise temporal calibration of dinosaur origins |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=3 |pages=509–513 |doi=10.1073/pnas.1512541112|pmid=26644579 |pmc=4725541 |bibcode=2016PNAS..113..509M |doi-access=free }}</ref> Dinosaurs may have appeared as early as the [[Anisian]] epoch of the Triassic, approximately 243&nbsp;million years ago, which is the age of ''[[Nyasasaurus]]'' from the [[Manda Formation]] of Tanzania. However, its known fossils are too fragmentary to identify it as a dinosaur or only a close relative.<ref name=nyasasaurus>{{cite journal |last1=Nesbitt |first1=Sterling J. |last2=Barrett |first2=Paul M. |last3=Werning |first3=Sarah |last4=Sidor |first4=Christian A. |author-link4=Christian Sidor |last5=Charig |first5=Alan J. |author-link5=Alan J. Charig |display-authors=3 |year=2012 |title=The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania |journal=[[Biology Letters]] |volume=9 |issue=1 |article-number=20120949 |location=London |publisher=Royal Society |doi=10.1098/rsbl.2012.0949 |issn=1744-9561 |pmc=3565515 |pmid=23221875}}</ref> The referral of the Manda Formation to the Anisian is also uncertain. Regardless, dinosaurs existed alongside non-dinosaurian ornithodirans for a period of time, with estimates ranging from 5–10 million years<ref name="marsicano2015">{{cite journal |last1=Marsicano |first1=C.A. |last2=Irmis |first2=R.B. |last3=Mancuso |first3=A.C. |last4=Mundil |first4=R. |last5=Chemale |first5=F. |year=2015 |title=The precise temporal calibration of dinosaur origins |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=3 |pages=509–513 |doi=10.1073/pnas.1512541112 |pmid=26644579 |pmc=4725541 |bibcode=2016PNAS..113..509M |issn=0027-8424 |doi-access=free}}</ref> to 21 million years.<ref name="langer18"/>

When dinosaurs appeared, they were not the dominant terrestrial animals. The terrestrial habitats were occupied by various types of [[Archosauromorpha|archosauromorphs]] and [[therapsid]]s, like [[cynodont]]s and [[rhynchosaur]]s. Their main competitors were the [[pseudosuchians]], such as [[aetosaur]]s, [[ornithosuchidae|ornithosuchids]] and rauisuchians, which were more successful than the dinosaurs.<ref>{{cite journal |last1=Brusatte |first1=Stephen L. |author-link1=Stephen L. Brusatte |last2=Benton |first2=Michael J. |last3=Ruta |first3=Marcello |author-link3=Marcello Ruta |last4=Lloyd |first4=Graeme T. |year=2008 |title=Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs |url=https://www.pure.ed.ac.uk/ws/files/8232088/PDF_Brusatteetal2008SuperiorityCompetition.pdf |archive-url=https://web.archive.org/web/20180719005836/https://www.pure.ed.ac.uk/ws/files/8232088/PDF_Brusatteetal2008SuperiorityCompetition.pdf |archive-date=2018-07-19 |url-status=live |journal=Science |location=Washington, D.C. |publisher=American Association for the Advancement of Science |volume=321 |issue=5895 |pages=1485–1488 |doi=10.1126/science.1161833 |bibcode=2008Sci...321.1485B |issn=0036-8075 |pmid=18787166 |access-date=October 22, 2019|hdl=20.500.11820/00556baf-6575-44d9-af39-bdd0b072ad2b |s2cid=13393888 }}</ref> Most of these other animals became extinct in the Triassic, in one of two events. First, at about 215&nbsp;million years ago, a variety of [[Basal (phylogenetics)|basal]] archosauromorphs, including the [[Protorosauria|protorosaurs]], became extinct. This was followed by the Triassic–Jurassic extinction event (about 201&nbsp;million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, [[phytosaur]]s, and rauisuchians. Rhynchosaurs and [[dicynodont]]s survived (at least in some areas) at least as late as early –mid [[Norian]] and late Norian or earliest [[Rhaetian]] [[Stage (stratigraphy)|stage]]s, respectively,<ref>{{harvnb|Tanner|Spielmann|Lucas|2013|pp=[https://econtent.unm.edu/digital/collection/bulletins/id/1688 562–566]|loc="The first Norian (Revueltian) rhynchosaur: Bull Canyon Formation, New Mexico, U.S.A." by Justin A. Spielmann, Spencer G. Lucas and [[Adrian P. Hunt]].}}</ref><ref>{{cite journal |last1=Sulej |first1=Tomasz |last2=Niedźwiedzki |first2=Grzegorz |year=2019 |title=An elephant-sized Late Triassic synapsid with erect limbs |journal=Science |location=Washington, D.C. |publisher=American Association for the Advancement of Science |volume=363 |issue=6422 |pages=78–80 |doi=10.1126/science.aal4853 |issn=0036-8075 |pmid=30467179|bibcode=2019Sci...363...78S |s2cid=53716186 |doi-access=free }}</ref> and the exact date of their [[extinction]] is uncertain. These losses left behind a land fauna of [[crocodylomorpha|crocodylomorphs]], dinosaurs, mammals, pterosaurians, and [[turtle]]s.<ref name=MJB04dino/> The first few lines of early dinosaurs [[Adaptive radiation|diversified]] through the Carnian and Norian stages of the Triassic, possibly by occupying the niches of the groups that became extinct.<ref name="Letal05"/> Also notably, there was a heightened rate of extinction during the [[Carnian pluvial episode|Carnian pluvial event]].<ref>{{cite news |author=<!--Staff writer(s); no by-line.--> |date=April 19, 2018 |title=Fossil tracks in the Alps help explain dinosaur evolution |url=https://www.economist.com/science-and-technology/2018/04/19/fossil-tracks-in-the-alps-help-explain-dinosaur-evolution |url-access=registration |department=Science and Technology |newspaper=[[The Economist]] |location=London |issn=0013-0613 |access-date=May 24, 2018}}</ref>

===Evolution and paleobiogeography===
[[File:Pangaea 200Ma.jpg|thumb|upright=1.5|The supercontinent [[Pangaea]] in the early [[Mesozoic]] (around 200 million years ago)]]
Dinosaur evolution after the Triassic followed changes in vegetation and the location of continents. In the Late Triassic and Early Jurassic, the continents were connected as the single landmass [[Pangaea]], and there was a worldwide dinosaur fauna mostly composed of [[coelophysoidea|coelophysoid]] carnivores and early sauropodomorph herbivores.<ref name=HCL04/> [[Gymnosperm]] plants (particularly [[Pinophyta|conifer]]s), a potential food source, [[Evolutionary radiation|radiated]] in the Late Triassic. Early sauropodomorphs did not have sophisticated mechanisms for processing food in the mouth, and so must have employed other means of breaking down food farther along the digestive tract.<ref name=FS04/> The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of [[ceratosauria]]ns, [[Megalosauroidea|megalosauroids]], and [[Allosauroidea|allosauroids]], and herbivores consisting of stegosaurian ornithischians and large sauropods. Examples of this include the [[Morrison Formation]] of [[North America]] and [[Tendaguru Formation|Tendaguru Beds]] of Tanzania. Dinosaurs in China show some differences, with specialized [[Metriacanthosauridae|metriacanthosaurid]] theropods and unusual, long-necked sauropods like ''[[Mamenchisaurus]]''.<ref name=HCL04/> Ankylosaurians and ornithopods were also becoming more common, but primitive sauropodomorphs had become extinct. Conifers and [[pteridophyte]]s were the most common plants. Sauropods, like earlier sauropodomorphs, were not oral processors, but ornithischians were evolving various means of dealing with food in the mouth, including potential [[cheek]]-like organs to keep food in the mouth, and jaw motions to grind food.<ref name=FS04/> Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians.<ref name=KP04/>

By the [[Early Cretaceous]] and the ongoing breakup of Pangaea, dinosaurs were becoming strongly differentiated by landmass. The earliest part of this time saw the spread of ankylosaurians, [[iguanodontia]]ns, and [[brachiosauridae|brachiosaurids]] through Europe, North America, and northern [[Africa]]. These were later supplemented or replaced in Africa by large spinosaurid and [[carcharodontosauridae|carcharodontosaurid]] theropods, and [[rebbachisauridae|rebbachisaurid]] and [[titanosauria]]n sauropods, also found in [[South America]]. In [[Asia]], maniraptoran coelurosaurians like dromaeosaurids, [[troodontidae|troodontids]], and [[oviraptorosauria]]ns became the common theropods, and [[ankylosauridae|ankylosaurids]] and early ceratopsians like ''Psittacosaurus'' became important herbivores. Meanwhile, [[Australia]] was home to a fauna of basal ankylosaurians, [[hypsilophodont]]s, and iguanodontians.<ref name=HCL04/> The stegosaurians appear to have gone extinct at some point in the late Early Cretaceous or early [[Late Cretaceous]]. A major change in the Early Cretaceous, which would be amplified in the Late Cretaceous, was the evolution of [[flowering plant]]s. At the same time, several groups of dinosaurian herbivores evolved more sophisticated ways to orally process food. Ceratopsians developed a method of slicing with teeth stacked on each other in batteries, and iguanodontians refined a method of grinding with [[Dinosaur tooth#Dental batteries|dental batteries]], taken to its extreme in hadrosaurids.<ref name=FS04/> Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid ''[[Nigersaurus]]''.<ref name=serenoetal07/>

There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were tyrannosaurids and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurians. In the southern continents that had made up the now-splitting supercontinent [[Gondwana]], [[abelisauridae|abelisaurids]] were the common theropods, and titanosaurian sauropods the common herbivores. Finally, in Europe, dromaeosaurids, [[rhabdodontidae|rhabdodontid]] iguanodontians, [[nodosauridae|nodosaurid]] ankylosaurians, and titanosaurian sauropods were prevalent.<ref name=HCL04/> Flowering plants were greatly radiating,<ref name=FS04/> with the first grasses appearing by the end of the Cretaceous.<ref name=PSAS05/> Grinding hadrosaurids and shearing ceratopsians became very diverse across North America and Asia. Theropods were also radiating as herbivores or [[omnivore]]s, with [[Therizinosauria|therizinosaur]]ians and [[ornithomimosauria]]ns becoming common.<ref name=FS04/>

The Cretaceous–Paleogene extinction event, which occurred approximately 66&nbsp;million years ago at the end of the Cretaceous, caused the extinction of all dinosaur groups except for the neornithine birds. Some other diapsid groups, including [[crocodilia]]ns, [[Dyrosauridae|dyrosaurs]], [[sebecosuchia]]ns, turtles, [[lizard]]s, [[snake]]s, [[Rhynchocephalia|sphenodontia]]ns, and [[choristodera]]ns, also survived the event.<ref name=AF04/>

The surviving lineages of neornithine birds, including the ancestors of modern [[ratite]]s, [[Fowl|ducks and chickens]], and a variety of [[Charadriiformes|waterbirds]], diversified rapidly at the beginning of the [[Paleogene]] period, entering [[ecological niche]]s left vacant by the extinction of Mesozoic dinosaur groups such as the arboreal [[enantiornithine]]s, aquatic [[hesperornithine]]s, and even the larger terrestrial theropods (in the form of ''[[Gastornis]]'', [[Eogruidae|eogruiids]], [[bathornithids]], ratites, [[Geranoididae|geranoidids]], [[mihirung]]s, and "[[terror bird]]s"). It is often stated that mammals out-competed the neornithines for dominance of most terrestrial niches but many of these groups co-existed with rich mammalian faunas for most of the [[Cenozoic]] Era.<ref name=lindow>{{harvnb|Dyke|Kaiser|2011|loc=chpt. 14: "Bird Evolution Across the K–Pg Boundary and the Basal Neornithine Diversification" by Bent E. K. Lindow. {{doi|10.1002/9781119990475.ch14}}}}</ref> Terror birds and bathornithids occupied carnivorous guilds alongside predatory mammals,<ref name="Cracraft">{{cite journal |last=Cracraft |first=Joel |author-link=Joel Cracraft |year=1968 |title=A Review of the Bathornithidae (Aves, Gruiformes), with Remarks on the Relationships of the Suborder Cariamae |url=https://www.biodiversitylibrary.org/item/328644#page/1/mode/1up |journal=[[American Museum Novitates]] |location=New York |publisher=American Museum of Natural History |issue=2326 |pages=1–46 |issn=0003-0082 |hdl=2246/2536 |access-date=January 30, 2026|url-status=live
|archive-url= https://archive.org/details/reviewbathornit2326crac/reviewbathornit2326crac/page/6/mode/2up |archive-date= November 13, 2023 }}</ref><ref>{{cite journal |last1=Alvarenga |first1=Herculano |author1-link=Herculano Marcos Ferraz de Alvarenga |last2=Jones |first2=Washington W. |last3=Rinderknecht |first3=Andrés |date=May 2010 |title=The youngest record of phorusrhacid birds (Aves, Phorusrhacidae) from the late Pleistocene of Uruguay |url=https://www.researchgate.net/publication/233512584 |journal=[[Neues Jahrbuch für Geologie und Paläontologie]] |location=[[Stuttgart]] |publisher=[[E. Schweizerbart]] |volume=256 |issue=2 |pages=229–234 |doi=10.1127/0077-7749/2010/0052 |bibcode=2010NJGPA.256..229A |issn=0077-7749 |access-date=October 22, 2019}}</ref> and ratites are still fairly successful as midsized herbivores; eogruiids similarly lasted from the [[Eocene]] to [[Pliocene]], becoming extinct only very recently after over 20&nbsp;million years of co-existence with many mammal groups.<ref>{{harvnb|Mayr|2009}}</ref>

==Classification==
{{Main|Dinosaur classification}}

{{multiple image
| align             = right
| perrow            = 2/2
| total_width       = 350
| image1            = Saurischia pelvis.png
| alt1              = 
| caption1          = [[Saurischia]]n pelvis structure (left side)
| image2            = Tyrannosaurus pelvis left.jpg
| alt2              = 
| caption2          = ''[[Tyrannosaurus]]'' pelvis (showing saurischian structure&nbsp;– left side)
| image3            = Ornithischia pelvis.png
| alt3              = 
| caption3          = [[Ornithischia]]n pelvis structure (left side)
| image4            = Edmontosaurus pelvis left.jpg
| alt4              = 
| caption4          = ''[[Edmontosaurus]]'' pelvis (showing ornithischian structure&nbsp;– left side)
}}

Dinosaurs belong to a group known as archosaurs, which also includes modern crocodilians. Within the archosaur group, dinosaurs are differentiated most noticeably by their gait. Dinosaur legs extend directly beneath the body, whereas the legs of lizards and crocodilians sprawl out to either side.<ref name="B012"/>

Collectively, dinosaurs as a clade are divided into two primary branches, Saurischia and Ornithischia. Saurischia includes those taxa sharing a more recent common ancestor with birds than with Ornithischia, while Ornithischia includes all [[taxon|taxa]] sharing a more recent common ancestor with ''Triceratops'' than with Saurischia. Anatomically, these two groups can be distinguished most noticeably by their [[pelvis|pelvic]] structure. Early saurischians—"lizard-hipped", from the [[Ancient Greek|Greek]] ''{{lang|grc-Latn|sauros}}'' ({{lang|grc|σαῦρος}}) meaning "lizard" and ''{{lang|grc-Latn|ischion}}'' ({{lang|grc|ἰσχίον}}) meaning "hip joint"—retained the hip structure of their ancestors, with a pubis bone directed [[anatomical terms of location|cranially]], or forward.<ref name=MJB00/> This basic form was modified by rotating the pubis backward to varying degrees in several groups (''Herrerasaurus'',<ref name=GSP88/> therizinosauroids,<ref name=clarketal2004/> dromaeosaurids,<ref name=MAPM04/> and birds<ref name=KP04/>). Saurischia includes the theropods (exclusively bipedal and with a wide variety of diets) and sauropodomorphs (long-necked herbivores which include advanced, quadrupedal groups).<ref name=theropods/><ref name=sauropodomorphs>{{cite journal |last1=Taylor |first1=Michael P. |author-link1=Michael P. Taylor |last2=Wedel |first2=Mathew J. |author-link2=Matt Wedel |year=2013 |title=Why sauropods had long necks; and why giraffes have short necks |journal=[[PeerJ]] |location=[[Corte Madera, California|Corte Madera, CA]]; London |volume=1 |article-number=e36 |doi=10.7717/peerj.36 |issn=2167-8359 |pmid=23638372 |pmc=3628838 |doi-access=free }}</ref>

By contrast, ornithischians—"bird-hipped", from the Greek ''ornis'' (ὀρνίς) meaning "bird" and ''ischion'' (ἰσχίον) meaning "hip joint"—had a pelvis that superficially resembled a bird's pelvis: the pubic bone was oriented caudally (rear-pointing). Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of species that were primarily herbivores.

Despite the terms "bird hip" (Ornithischia) and "lizard hip" (Saurischia), birds are not part of Ornithischia. Birds instead belong to Saurischia, the "lizard-hipped" dinosaurs—birds evolved from earlier dinosaurs with "lizard hips".<ref name="B012"/>

The following cladogram showing the relationships of dinosaur groups is simplified after Michael Benton, 2015:<ref name="MJB00" />

{{clade |style=line-height:75%;font-size:85%
|label1='''Dinosauria'''
|1={{clade
  |label1=[[Saurischia]]
  |1={{clade
    |1=[[Herrerasauridae]] [[File:Herrerasaurus TD.png|60 px]]
    |2={{clade
      |label1=[[Theropoda]]
      |1={{clade
        |1=[[Coelophysoidea]][[File:Coelophysis TD.png|60 px]]
        |2={{clade
          |1=[[Ceratosauria]] [[File:Carnotaurus TD.png|60 px]]
          |label2=[[Tetanurae]]
          |2={{clade
            |1=[[Megalosauroidea]] [[File:Spinosaurus TD.png|60px]]
            |2={{clade
              |1=[[Allosauroidea]] [[File:Allosaurus TD.png|60px]]
              |label2=[[Coelurosauria]]
              |2={{clade
                |1=[[Tyrannosauroidea]] [[File:Tyrannosaurus TD.png|60 px]]
                |2={{clade
                  |1=[[Compsognathidae]] [[File:Compsognathus TD.png|60px]]
                  |2={{clade
                    |1=[[Ornithomimidae]] [[File:Ornithomimus TD.png|60px]]
                    |label2=[[Maniraptora]]
                    |2={{clade hidden |id=2 |mode=left
                      |expand-text=&nbsp;(including birds) [[File:Deinonychus TD.png|60px]]
                      |1=[[Alvarezsauridae]] [[File:Shuvuuia TD.png|60px]]
                      |2={{clade
                        |1=[[Therizinosauridae]] [[File:Therizinosaurus TD.png|60px]]
                        |2={{clade
                          |1=[[Oviraptorosauria]] [[File:Oviraptor TD.png|60px]]
                          |label2=[[Paraves]]
                          |2={{clade
                            |1=[[Deinonychosauria]] [[File:Deinonychus TD.png|60px]]
                            |2=[[Aves]] (birds) [[File:Kunpengornis TD.png|60px]]
                            }}
                          }}
                        }}
                      }}
                    }}
                  }}
                }}
              }}
            }}
          }}
        }}
      |label2=[[Sauropodomorpha]]
      |2={{clade
        |1=[[Plateosauridae]] [[File:Plateosaurus TD.png|60px]]
        |2={{clade
          |1=[[Riojasauridae]] 
          |2={{clade
            |1=[[Massospondylidae]] [[File:Massospondylus TD.png|60px]]
            |label2=[[Sauropoda]] 
            |2={{clade
              |1=[[Vulcanodontidae]] [[File:Barapasaurus TD.png|60px]]
              |2={{clade
                |1=[[Mamenchisauridae]] [[File:Tongnanlong TD.png|60px]]
                |label2=[[Neosauropoda]]
                |2={{clade
                  |1=[[Diplodocoidea]] [[File:Diplodocus TD.png|60px]]
                  |label2=[[Macronaria]]
                  |2={{clade hidden |id=2 |mode=left
                    |expand-text= [[File:Brachiosaurus TD.png|60px]]
                    |1=[[Camarasauridae]] [[File:Camarasaurus TD.png|60px]]
                    |2={{clade
                      |1=[[Brachiosauridae]] [[File:Brachiosaurus TD.png|60px]]
                      |2=[[Titanosauria]] [[File:Qunkasaura TD.png|60px]]
                      }}
                    }}
                  }}
                }}
              }}
            }}
          }}
        }}
      }}
    }}
  |label2=[[Ornithischia]]
  |2={{clade
    |1=[[Heterodontosauridae]] [[File:Heterodontosaurus TD.png|60px]]
    |2={{clade
      |label1=[[Thyreophora]]
      |1={{clade
        |1=[[Stegosauria]] [[File:Stegosaurus TD.png|60px]]
        |2=[[Ankylosauria]] [[File:Ankylosaurus TD.png|60px]]
        }}
      |label2=[[Cerapoda]]
      |2={{clade
        |label1=[[Marginocephalia]] 
        |1={{clade
          |1=[[Pachycephalosauria]] [[File:Pachycephalosaurus TD.png|60px]]
          |2=[[Ceratopsia]] [[File:Triceratops TD.png|60px]]
          }}
        |label2=[[Ornithopoda]]
        |2={{clade
          |1=''[[Iguanodon]]'' [[File:Iguanodon TD.png|60px]]
          |2=[[Hadrosauridae]] [[File:Corythosaurus TD.png|60px]]
          }}
        }}
      }}
    }}
  }}
}}

==Paleobiology==
Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including fossilized bones, [[feces]], [[Fossil trackway|trackway]]s, [[gastrolith]]s, [[feather]]s, impressions of skin, [[Organ (anatomy)|internal organ]]s and other [[soft tissue]]s.<ref name="softtissue">{{cite journal |last1=Dal Sasso |first1=Cristiano |author-link1=Cristiano Dal Sasso |last2=Signore |first2=Marco |date=March 26, 1998 |title=Exceptional soft-tissue preservation in a theropod dinosaur from Italy |journal=Nature |location=London |publisher=Nature Research |volume=392 |issue=6674 |pages=383–387 |doi=10.1038/32884 |bibcode=1998Natur.392..383D |s2cid=4325093 |issn=0028-0836|url=http://doc.rero.ch/record/14901/files/PAL_E2043.pdf |archive-url=https://web.archive.org/web/20160920170653/https://doc.rero.ch/record/14901/files/PAL_E2043.pdf |archive-date=2016-09-20 |url-status=live }}</ref><ref name="Schweitzer2005"/> Many fields of study contribute to our understanding of dinosaurs, including [[physics]] (especially [[biomechanics]]), [[chemistry]], [[biology]], and the [[Earth science]]s (of which [[paleontology]] is a sub-discipline).<ref name=alexander2006/><ref name=dinobiology>{{cite journal |last1=Farlow |first1=James O. |last2=Dodson |first2=Peter |last3=Chinsamy |first3=Anusuya |author-link3=Anusuya Chinsamy-Turan |date=November 1995 |title=Dinosaur Biology |journal=[[Annual Review of Ecology, Evolution, and Systematics|Annual Review of Ecology and Systematics]] |location=[[Palo Alto, California|Palo Alto, CA]] |publisher=[[Annual Reviews (publisher)|Annual Reviews]] |volume=26 |issue=1 |pages=445–471 |doi=10.1146/annurev.es.26.110195.002305 |bibcode=1995AnRES..26..445F |issn=1545-2069}}</ref> Two topics of particular interest and study have been dinosaur size and behavior.<ref>{{harvnb|Weishampel|Dodson|Osmólska|2004}}</ref>

===Size===
{{Main|Dinosaur size}}

[[File:Longest dinosaur by clade.svg|alt=|thumb|upright=1.35 |Scale diagram comparing the average human to the longest known dinosaurs in five major [[clade]]s:{{legend|#b1293a|[[Sauropoda]] (''[[Supersaurus|Supersaurus vivianae]]'')}}{{legend|#cf52cf|[[Ornithopod]]a (''[[Shantungosaurus|Shantungosaurus giganteus]]'')}}{{legend|#59ca4e|[[Theropoda]] (''[[Spinosaurus|Spinosaurus aegyptiacus]]'')}}
{{legend|#f89451|[[Thyreophora]] (''[[Stegosaurus|Stegosaurus ungulatus]]'')}}
{{legend|#2e538c|[[Marginocephalia]] (''[[Triceratops|Triceratops prorsus]]'')}}]]

Current evidence suggests that dinosaur average size varied through the Triassic, Early Jurassic, Late Jurassic and Cretaceous.<ref name=Sereno1999/> Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the {{convert|100|to|1000|kg|lb|abbr=on|adj=on}} category when sorted by estimated weight into categories based on [[order of magnitude]], whereas [[Holocene|recent]] predatory carnivoran mammals peak in the {{convert|10|to|100|kg|lb|abbr=on|adj=on}} category.<ref name=JF93/> The [[Mode (statistics)|mode]] of Mesozoic dinosaur body masses is between {{convert|1|and|10|MT|ST}}.<ref name=Peczkis1994/> This contrasts sharply with the average size of Cenozoic mammals, estimated by the [[National Museum of Natural History]] as about {{convert|2|to|5|kg|lb|abbr=on}}.<ref name=NMNH/>

The sauropods were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest was an order of magnitude more massive than anything else that has since walked the Earth. Giant prehistoric mammals such as ''[[Paraceratherium]]'' (the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in size.<ref name="sander2011">{{cite journal |last1=Sander |first1=P. Martin |last2=Christian |first2=Andreas |last3=Clauss |first3=Marcus |last4=Fechner |first4=Regina |last5=Gee |first5=Carole T. |last6=Griebeler |first6=Eva-Maria |last7=Gunga |first7=Hanns-Christian |last8=Hummel |first8=Jürgen |last9=Mallison |first9=Heinrich |display-authors=3 |date=February 2011 |title=Biology of the sauropod dinosaurs: the evolution of gigantism |journal=Biological Reviews |location=Cambridge |publisher=Cambridge Philosophical Society |volume=86 |issue=1 |pages=117–155 |doi=10.1111/j.1469-185X.2010.00137.x |issn=1464-7931 |pmid=21251189 |pmc=3045712}}</ref> There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments.<ref name=KC06/>

====Largest and smallest====
Scientists will probably never be certain of the [[largest organisms|largest and smallest dinosaurs]] to have ever existed. This is because only a tiny percentage of animals were ever fossilized and most of these remain buried in the earth. Few non-avian dinosaur specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork.<ref>{{harvnb|Paul|2010}}</ref>

[[File:Argentinosaurus 9.svg|thumb|upright=1.15|left|Comparative size of ''[[Argentinosaurus]]'' to the average human]]
The tallest and heaviest dinosaur known from good skeletons is ''[[Giraffatitan|Giraffatitan brancai]]'' (previously classified as a species of ''[[Brachiosaurus]]''). Its remains were discovered in Tanzania between 1907 and 1912. Bones from several similar-sized individuals were incorporated into the skeleton now mounted and on display at the [[Natural History Museum, Berlin|Museum für Naturkunde]] in [[Berlin]];<ref name=EC68/> this mount is {{convert|12|m|ft|sp=us}} tall and {{convert|21.8|to|22.5|m|ft|sp=us}} long,<ref>{{cite journal |last1=Mazzetta |first1=Gerardo V. |last2=Christiansenb |first2=Per |last3=Fariñaa |first3=Richard A. |year=2004 |title=Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs |url=http://www.miketaylor.org.uk/tmp/papers/Mazzetta-et-al_04_SA-dino-body-size.pdf |archive-url=https://web.archive.org/web/20090225155217/http://www.miketaylor.org.uk/tmp/papers/Mazzetta-et-al_04_SA-dino-body-size.pdf |archive-date=2009-02-25 |url-status=live |journal=Historical Biology |location=Milton Park, Oxfordshire |publisher=Taylor & Francis |volume=16 |issue=2–4 |pages=71–83 |doi=10.1080/08912960410001715132 |bibcode=2004HBio...16...71M |citeseerx=10.1.1.694.1650 |s2cid=56028251 |issn=0891-2963}}</ref><ref>{{cite journal |last=Janensch |first=Werner |author-link=Werner Janensch |year=1950 |others=Translation by Gerhard Maier |title=Die Skelettrekonstruktion von ''Brachiosaurus brancai'' |trans-title=The Skeleton Reconstruction of Brachiosaurus brancai |url=https://paleoglot.org/files/Janensch1950b.pdf |url-status=live |journal=Palaeontographica |location=Stuttgart |publisher=[[E. Schweizerbart]] |volume=Suplement VII |issue=1. Reihe, Teil 3, Lieferung 2 |pages=97–103 |oclc=45923346 |archive-url=https://web.archive.org/web/20170711052046/https://paleoglot.org/files/Janensch1950b.pdf |archive-date=July 11, 2017 |access-date=October 24, 2019}}</ref> and would have belonged to an animal that weighed between {{gaps|30|000}} and {{gaps|60|000}}&nbsp;kilograms ({{gaps|70|000}} and {{gaps|130|000}}&nbsp;lb). The longest complete dinosaur is the {{convert|27|m|ft|sp=us}} long ''Diplodocus'', which was discovered in [[Wyoming]] in the [[United States]] and displayed in [[Pittsburgh]]'s [[Carnegie Museum of Natural History]] in 1907.<ref name=lucas04>{{cite conference |last1=Lucas |first1=Spencer G. |last2=Herne |first2=Matthew C. |last3=Hecket |first3=Andrew B. |last4=Hunt |first4=Adrian P. |last5=Sullivan |first5=Robert M. |display-authors=3 |year=2004 |title=Reappraisal of ''Seismosaurus'', a Late Jurassic Sauropod Dinosaur From New Mexico |url=https://gsa.confex.com/gsa/2004AM/finalprogram/abstract_77727.htm |url-status=live |conference=2004 Denver Annual Meeting (November 7–10, 2004) |conference-url=https://gsa.confex.com/gsa/2004AM/webprogram/start.html |volume=36 |publisher=Geological Society of America |location=Boulder, CO |page=422 |id=Paper No. 181-4 |oclc=62334058 |archive-url=https://web.archive.org/web/20191008110318/https://gsa.confex.com/gsa/2004AM/finalprogram/abstract_77727.htm |archive-date=October 8, 2019 |access-date=October 25, 2019}}</ref> The longest dinosaur known from good fossil material is ''[[Patagotitan]]'': the skeleton mount in the American Museum of Natural History in [[New York City|New York]] is {{convert|37|meters|feet}} long. The [[Museo Carmen Funes|Museo Municipal Carmen Funes]] in [[Plaza Huincul]], Argentina, has an ''[[Argentinosaurus]]'' reconstructed skeleton mount that is {{convert|39.7|m|feet|sp=us}} long.<ref name="PLOS One">{{cite journal |last1=Sellers |first1=William Irvin. |last2=Margetts |first2=Lee |last3=Coria |first3=Rodolfo Aníbal |author3-link=Rodolfo Coria |last4=Manning |first4=Phillip Lars |year=2013 |editor1-last=Carrier |editor1-first=David |title=March of the Titans: The Locomotor Capabilities of Sauropod Dinosaurs |doi=10.1371/journal.pone.0078733 |journal=PLOS ONE |location=San Francisco, CA |publisher=PLOS |volume=8 |issue=10 |article-number=e78733 |pmid=24348896 |pmc=3864407|bibcode=2013PLoSO...878733S |issn=1932-6203|doi-access=free }}</ref>

[[File:Bruhathkayosaurus matleyi updated.png|thumb|upright=1.15|right|''[[Bruhathkayosaurus]]'', potentially the largest terrestrial animal to ever exist]]
There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were discovered in the 1970s or later, and include the massive ''Argentinosaurus'', which may have weighed {{convert|80000|to|100000|kg|ST|sp=us|abbr=off|comma=gaps}} and reached lengths of {{convert|30|to|40|m|ft|sp=us}}; some of the longest were the {{convert|33.5|m|ft|sp=us|adj=mid}} long ''Diplodocus hallorum''<ref name=KC06/> (formerly ''Seismosaurus''), the {{convert|33|to|34|m|ft|sp=us|adj=mid}} long ''[[Supersaurus]]'',<ref name=LHW07/> and {{convert|37|m|feet|sp=us|adj=mid}} long ''Patagotitan''; and the tallest, the {{convert|18|m|ft|sp=us|adj=mid}} tall ''[[Sauroposeidon]]'', which could have reached a sixth-floor window. There were a few dinosaurs that were considered either the heaviest or longest. The most famous include ''[[Amphicoelias fragillimus]]'', known only from a now lost partial vertebral [[Vertebra#Structure|neural arch]] described in 1878. Extrapolating from the illustration of this bone, the animal may have been {{convert|58|m|ft|sp=us}} long and weighed {{cvt|122400|kg|lb|comma=gaps}}.<ref name=KC06/> However, recent research has reclassified ''Amphicoelias'' from the long, gracile diplodocid to the shorter but much stockier rebbachisaurid. Now renamed as ''[[Maraapunisaurus]]'', this sauropod measured as much as {{convert|40|m|ft|sp=us}} long and weighed as much as {{cvt|120000|kg|lb|comma=gaps}}.<ref name="carpenter2018">{{cite journal | title=Maraapunisaurus fragillimus, N.G. (formerly Amphicoelias fragillimus), a basal Rebbachisaurid from the Morrison Formation (Upper Jurassic) of Colorado | author=Carpenter, Kenneth | journal=Geology of the Intermountain West | year=2018 | volume=5 | pages=227–244 | doi=10.31711/giw.v5i0.28 | doi-access=free }}</ref><ref>{{Cite journal|last=Paul|first=Gregory S.|date=2019|title=Determining the largest known land animal: A critical comparison of differing methods for restoring the volume and mass of extinct animals|url=http://www.gspauldino.com/Titanomass.pdf|journal=Annals of the Carnegie Museum|volume=85|issue=4|pages=335–358|doi=10.2992/007.085.0403|bibcode=2019AnCM...85..335P|s2cid=210840060|archive-date=January 28, 2020|access-date=December 2, 2023|archive-url=https://web.archive.org/web/20200128092205/http://www.gspauldino.com/Titanomass.pdf|url-status=live}}</ref> Another contender of this title includes ''[[Bruhathkayosaurus]]'', a controversial taxon that was recently confirmed to exist after archived photos were uncovered.<ref>{{Cite journal |last1=Pal |first1=Saurabh |last2=Ayyasami |first2=Krishnan |date=27 June 2022 |title=The lost titan of Cauvery |journal=[[Geology Today]] |language=en |volume=38 |issue=3 |pages=112–116 |doi=10.1111/gto.12390 |bibcode=2022GeolT..38..112P |s2cid=250056201 |issn=0266-6979}}</ref> ''Bruhathkayosaurus'' was a titanosaur and would have most likely weighed more than even ''Maraapunisaurus''. Recent size estimates in 2023 have this sauropod reaching lengths of up to {{cvt|44|m|ft}} long and placed in a colossal weight range of around {{cvt|110000–170000|kg|lb|comma=gaps}}. If these upper estimates are true, ''Bruhathkayosaurus'' would have rivaled the [[blue whale]] and ''[[Perucetus colossus]]'' as one of the largest animals to have ever existed.<ref name="Bruhathkayosaurus2023">{{Cite journal |last1=Paul |first1=Gregory S. |last2=Larramendi |first2=Asier |date=11 April 2023 |title=Body mass estimate of ''Bruhathkayosaurus'' and other fragmentary sauropod remains suggest the largest land animals were about as big as the greatest whales |journal=Lethaia |language=en |volume=56 |issue=2 |pages=1–11 |doi=10.18261/let.56.2.5 |bibcode=2023Letha..56..2.5P |s2cid=259782734 |issn=0024-1164|doi-access=free }}</ref>

The largest carnivorous dinosaur was ''[[Spinosaurus]]'', reaching a length of {{convert|12.6|to|18|m|ft|sp=us}} and weighing {{convert|7|to|20.9|MT|ST}}.<ref name=SMBM06/><ref name=TH07/> Other large carnivorous theropods included ''[[Giganotosaurus]]'', ''[[Carcharodontosaurus]]'', and ''Tyrannosaurus''.<ref name=TH07/> ''[[Therizinosaurus]]'' and ''[[Deinocheirus]]'' were among the tallest of the theropods. The largest ornithischian dinosaur was probably the hadrosaurid ''[[Shantungosaurus|Shantungosaurus giganteus]]'', which measured {{convert|16.6|m|feet|sp=us}}.<ref>{{cite journal |last1=Zhao |first1=Xijin |author1-link=Zhao Xijin |last2=Li |first2=Dunjing |last3=Han |first3=Gang |last4=Zhao |first4=Huaxi |last5=Liu |first5=Fengguang |last6=Li |first6=Laijin |last7=Fang |first7=Xiaosi |display-authors=3 |year=2007 |title=Zhuchengosaurus maximus from Shandong Province |journal=Acta Geoscientia Sinica |location=[[Beijing]] |publisher=[[Chinese Academy of Geological Sciences]] |volume=28 |issue=2 |pages=111–122 |issn=1006-3021}}</ref> The largest individuals may have weighed as much as {{convert|16|MT|ST}}.<ref>{{harvnb|Weishampel|Dodson|Osmólska|2004|pp=438–463|loc=chpt. 20: "Hadrosauridae" by John R. Horner David B. Weishampel, and Catherine A. Forster.}}</ref>

[[File:Bee hummingbird (Mellisuga helenae) adult male in flight-cropped.jpg|thumb|An adult [[bee hummingbird]], the smallest known dinosaur]]
The smallest dinosaur known is the [[bee hummingbird]],<ref>{{harvnb|Norell|Gaffney|Dingus|2000}}</ref> with a length of only {{convert|5|cm|in|sp=us}} and mass of around {{convert|1.8|g|oz|abbr=on}}.<ref>{{cite web |url=https://www.birds.com/species/a-b/bee-hummingbird/ |url-status=live |title=Bee Hummingbird (''Mellisuga helenae'') |website=Birds.com |publisher=Paley Media |archive-url=https://web.archive.org/web/20150403005328/https://www.birds.com/species/a-b/bee-hummingbird/ |archive-date=April 3, 2015 |access-date=October 27, 2019}}</ref> The smallest known non-[[Avialae|avialan]] dinosaurs were about the size of [[pigeon]]s and were those theropods most closely related to birds.<ref name=zhang2008/> For example, ''[[Anchiornis huxleyi]]'' is currently the smallest non-avialan dinosaur described from an adult specimen, with an estimated weight of {{convert|110|g|oz|abbr=on}}<ref name=anchiadvance/> and a total skeletal length of {{convert|34|cm|ft|sp=us}}.<ref name=zhang2008/><ref name=anchiadvance/> The smallest herbivorous non-avialan dinosaurs included ''[[Microceratus]]'' and ''[[Wannanosaurus]]'', at about {{convert|60|cm|ft|sp=us}} long each.<ref name=Holtz2007/><ref name="butler&zhao2009"/>

===Behavior===
[[File:Maiasaura nest (2).jpg|thumb|left|A nesting ground of the hadrosaur ''[[Maiasaura|Maiasaura peeblesorum]]'' was discovered in 1978]]

Many modern birds are highly social, often found living in flocks. There is general agreement that some behaviors that are common in birds, as well as in [[crocodilian]]s (closest living relatives of birds), were also common among extinct dinosaur groups. Interpretations of behavior in fossil species are generally based on the pose of skeletons and their [[Habitat (ecology)|habitat]], [[computer simulation]]s of their biomechanics, and comparisons with modern animals in similar ecological niches.<ref name=alexander2006/>

The first potential evidence for [[herd]]ing or [[Flocking (behavior)|flocking]] as a widespread behavior common to many dinosaur groups in addition to birds was the 1878 discovery of 31&nbsp;''Iguanodon'', ornithischians that were then thought to have perished together in [[Bernissart]], [[Belgium]], after they fell into a deep, flooded [[sinkhole]] and drowned.<ref name=Yans/> Other mass-death sites have been discovered subsequently. Those, along with multiple trackways, suggest that gregarious behavior was common in many early dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that duck-billed (hadrosaurids) may have moved in great herds, like the [[American bison]] or the African [[springbok]]. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in [[Oxfordshire]], England,<ref name=Day2002/> although there is no evidence for specific herd structures.<ref name=JLW05/> Congregating into herds may have evolved for defense, for [[Bird migration|migratory]] purposes, or to provide protection for young. There is evidence that many types of slow-growing dinosaurs, including various theropods, sauropods, ankylosaurians, ornithopods, and ceratopsians, formed aggregations of immature individuals. One example is a site in [[Inner Mongolia]] that has yielded remains of over 20 ''[[Sinornithomimus]]'', from one to seven years old. This assemblage is interpreted as a social group that was trapped in mud.<ref name=DVetal08sino/> The interpretation of dinosaurs as gregarious has also extended to depicting carnivorous theropods as [[pack hunter]]s working together to bring down large prey.<ref name=LG93/><ref name="maxwell&ostrom1995"/> However, this lifestyle is uncommon among modern birds, crocodiles, and other reptiles, and the [[taphonomy|taphonomic]] evidence suggesting mammal-like pack hunting in such theropods as ''Deinonychus'' and ''[[Allosaurus]]'' can also be interpreted as the results of fatal disputes between feeding animals, as is seen in many modern diapsid predators.<ref name=RB07/>

[[File:Centrosaurus dinosaur.png|thumb|upright=1.15|Restoration of two ''[[Centrosaurus|Centrosaurus apertus]]'' engaged in [[intra-specific combat]]]]
The crests and frills of some dinosaurs, like the [[marginocephalia]]ns, theropods and [[Lambeosaurinae|lambeosaurine]]s, may have been too fragile to be used for active defense, and so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and [[territory (animal)|territorialism]]. Head wounds from bites suggest that theropods, at least, engaged in active aggressive confrontations.<ref name=PC98/>

From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the [[Gobi Desert]] in 1971. It included a ''[[Velociraptor]]'' attacking a ''[[Protoceratops]]'',<ref name=AMNH/> providing evidence that dinosaurs did indeed attack each other.<ref name=carpenter1998/> Additional evidence for attacking live prey is the partially healed tail of an ''[[Edmontosaurus]]'', a hadrosaurid dinosaur; the tail is damaged in such a way that shows the animal was bitten by a tyrannosaur but survived.<ref name=carpenter1998/> [[Cannibalism (zoology)|Cannibalism]] amongst some species of dinosaurs was confirmed by tooth marks found in [[Madagascar]] in 2003, involving the theropod ''[[Majungasaurus]]''.<ref name=rogersetal2003/>

Comparisons between the [[scleral ring]]s of dinosaurs and modern birds and reptiles have been used to infer daily activity patterns of dinosaurs. Although it has been suggested that most dinosaurs were active during the day, these comparisons have shown that small predatory dinosaurs such as dromaeosaurids, ''[[Juravenator]]'', and ''[[Megapnosaurus]]'' were likely [[nocturnal]]. Large and medium-sized herbivorous and omnivorous dinosaurs such as ceratopsians, sauropodomorphs, hadrosaurids, ornithomimosaurs may have been [[cathemeral]], active during short intervals throughout the day, although the small ornithischian ''[[Agilisaurus]]'' was inferred to be [[Diurnality|diurnal]].<ref name=SchmitzMotani2011/>

Based on fossil evidence from dinosaurs such as ''[[Oryctodromeus]]'', some ornithischian species seem to have led a partially [[fossorial]] (burrowing) lifestyle.<ref name=VMK07/> Many modern birds are [[arboreal]] (tree climbing), and this was also true of many Mesozoic birds, especially the enantiornithines.<ref>{{harvnb|Chiappe|Witmer|2002}}</ref> While some early bird-like species may have already been arboreal as well (including dromaeosaurids) such as ''Microraptor''<ref name=chatterjee2007/>) most non-avialan dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, pioneered by [[Robert McNeill Alexander]], has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run,<ref name=alexander2006/> whether [[diplodocid]]s could create [[sonic boom]]s via [[whip]]-like tail snapping,<ref name=goriely/> and whether sauropods could float.<ref name=Henderson2006/>

===Communication===
[[File:Lambeosaurus magnicristatus DB.jpg|thumb|Restoration of a striking and unusual visual display in a ''[[Lambeosaurus|Lambeosaurus magnicristatus]]''. The crest may also have acted as a resonating chamber for sounds.]]

Modern birds [[Animal communication|communicate]] by visual and auditory signals, and the wide diversity of visual display structures among fossil dinosaur groups, such as horns, frills, crests, sails, and feathers, suggests that visual communication has always been important in dinosaur biology.<ref name=senter2008/> Reconstruction of the plumage color of ''Anchiornis'' suggest the importance of color in visual communication in non-avian dinosaurs.<ref name="Li2010"/> A 2009 review indicated that non-avians used visual displays and possibly non-vocal sounds, such as hissing, jaw-grinding or -clapping, splashing, and wing-beating (possible in winged maniraptoran dinosaurs).<ref name=senter2008/>

Fossilized [[larynx]]es or voice boxes have been identified in two dinosaurs; the ankylosaurid ''[[Pinacosaurus]]'' and the neornithischian ''[[Pulaosaurus]]'', the structures of which suggest that dinosaurs were capable of complex bird-like vocalizations.<ref name=":1" /><ref name="Yang2025"/> A 2016 study concludes that some dinosaurs may have produced closed-mouth vocalizations, such as cooing, hooting, and booming. These occur in both reptiles and birds and involve inflating the esophagus or tracheal pouches. Such vocalizations evolved independently in extant archosaurs numerous times, following increases in body size.<ref name="Tobias2016"/> The crests of some hadrosaurids and the nasal chambers of ankylosaurids may have been [[acoustic resonance|resonators]].<ref name="Weishampel981"/><ref name="Witmer"/> Birds have evolved a novel organ for vocalization, the [[Syrinx (bird anatomy)|syrinx]],<ref name=":22"/> the earliest remains of which were found in a specimen of the duck-like ''[[Vegavis|Vegavis iaai]]'' dated 69 –66&nbsp;million years ago.<ref name="Clarke2016"/> The syrinx may have supplemented and then replaced the larynx as a vocal organ during bird evolution.<ref name=":0" />

===Reproductive biology===
{{see also|Dinosaur egg}}
[[File:Gniazdo sieweczki RB.JPG|left|thumb|alt=Three bluish eggs with black speckling sit atop a layer of white mollusk shell pieces, surrounded by sandy ground and small bits of bluish stone|Nest of a [[plover]] (''[[Charadrius]]'')]]

All dinosaurs laid [[Amniote|amniotic egg]]s. Dinosaur eggs were usually laid in a nest. Most species create somewhat elaborate nests which can be cups, domes, plates, beds scrapes, mounds, or burrows.<ref name="Hansell">{{harvnb|Hansell|2000}}</ref> Some species of modern bird have no nests; the cliff-nesting [[Common murre|common guillemot]] lays its eggs on bare rock, and male [[emperor penguin]]s keep eggs between their body and feet. Primitive birds and many non-avialan dinosaurs often lay eggs in communal nests, with males primarily incubating the eggs. While modern birds have only one functional [[oviduct]] and lay one egg at a time, more primitive birds and other dinosaurs had two oviducts, like crocodiles. Some non-avialan dinosaurs, such as ''[[Troodon]]'', exhibited iterative laying, where the adult might lay a pair of eggs every one or two days, and then ensured simultaneous hatching by delaying [[Broodiness#Broodiness in non-avian animals|brooding]] until all eggs were laid.<ref name="Varrichioetal.02">{{cite journal |last1=Varricchio |first1=David J. |last2=Horner |first2=John R. |last3=Jackson |first3=Frankie D. |year=2002 |title=Embryos and eggs for the Cretaceous theropod dinosaur ''Troodon formosus'' |journal=Journal of Vertebrate Paleontology |location=Milton Park, Oxfordshire |publisher=Taylor & Francis for the Society of Vertebrate Paleontology |volume=22 |issue=3 |pages=564–576 |doi=10.1671/0272-4634(2002)022[0564:EAEFTC]2.0.CO;2 |s2cid=85728452 |issn=0272-4634}}</ref>

When laying eggs, females grow a special type of bone between the hard outer bone and the [[Bone marrow|marrow]] of their limbs. This [[medullary bone]], which is rich in [[calcium]], is used to make eggshells. A discovery of features in a ''Tyrannosaurus'' skeleton provided evidence of medullary bone in extinct dinosaurs and, for the first time, allowed paleontologists to establish the sex of a fossil dinosaur specimen. Further research has found medullary bone in the carnosaur ''Allosaurus'' and the ornithopod ''[[Tenontosaurus]]''. Because the line of dinosaurs that includes ''Allosaurus'' and ''Tyrannosaurus'' diverged from the line that led to ''Tenontosaurus'' very early in the evolution of dinosaurs, this suggests that the production of medullary tissue is a general characteristic of all dinosaurs.<ref name=LW08/>
[[File:Citipati AMNH.jpg|thumb|Fossil interpreted as a nesting [[oviraptoridae|oviraptorid]] ''[[Citipati]]'' at the [[American Museum of Natural History]]. ]]
Another widespread trait among modern birds (but see below in regards to fossil groups and extant [[megapodes]]) is parental care for young after hatching. [[Bob Makela]] and [[Jack Horner (paleontologist)|Jack Horner's]] 1978 discovery of a ''[[Maiasaura]]'' ("good mother lizard") nesting ground in Montana demonstrated that parental care continued long after birth among ornithopods.<ref name=HM79/> A specimen of the [[oviraptoridae|oviraptorid]] ''[[Citipati|Citipati osmolskae]]'' was discovered in a [[Chicken#Broodiness|chicken-like brooding position]] in 1993,<ref name="search.eb"/> which may indicate that they had begun using an insulating layer of feathers to keep the eggs warm.<ref>{{harvnb|Currie|Koppelhus|Shugar|Wright|2004|pp=[http://thomas-hopp.com/pdf/DinoBrooding.pdf 234–250]|loc=chpt. 11: "Dinosaur Brooding Behavior and the Origin of Flight Feathers" by Thomas P. Hopp and Mark J. Orsen.}}</ref> An embryo of the basal sauropodomorph ''[[Massospondylus]]'' was found without teeth, indicating that some parental care was required to feed the young dinosaurs.<ref name=Reiszetal05/> Trackways have also confirmed parental behavior among ornithopods from the [[Isle of Skye]] in northwestern [[Scotland]].<ref name=BBCtracks/>

However, there is ample evidence of [[precociality]] or [[Precociality#Superprecociality|superprecociality]] among many dinosaur species, particularly theropods. For instance, non-[[Euornithes|ornithuromorph]] birds have been abundantly demonstrated to have had slow growth rates, [[megapode]]-like egg burying behavior and the ability to fly soon after birth.<ref>{{cite journal |first1=Zhonghe |last1=Zhou |first2=Fucheng |last2=Zhang |year=2004 |title=A Precocial Avian Embryo from the Lower Cretaceous of China |journal=Science |location=Washington, D.C. |publisher=American Association for the Advancement of Science |volume=306 |issue=5696 |page=653 |doi=10.1126/science.1100000 |issn=0036-8075 |pmid=15499011|bibcode=2004Sci...306..653Z |s2cid=34504916 }}</ref><ref>{{cite journal |url=https://blogs.scientificamerican.com/tetrapod-zoology/drowned-cretaceous-bird-colony/ |url-status=live |title=A drowned nesting colony of Late Cretaceous birds |last=Naish |first=Darren |author-link=Darren Naish |date=May 15, 2012 |journal=Science |volume=306 |issue=5696 |page=653 |publisher=[[Scientific American#Website|Scientific American]] |doi=10.1126/science.1100000 |pmid=15499011 |bibcode=2004Sci...306..653Z |s2cid=34504916 |archive-url=https://web.archive.org/web/20180925031243/https://blogs.scientificamerican.com/tetrapod-zoology/drowned-cretaceous-bird-colony/ |archive-date=September 25, 2018 |access-date=November 16, 2019}}</ref><ref>{{cite journal |last1=Fernández |first1=Mariela S. |last2=García |first2=Rodolfo A. |last3=Fiorelli |first3=Lucas |last4=Scolaro |first4=Alejandro |last5=Salvador |first5=Rodrigo B. |last6=Cotaro |first6=Carlos N. |last7=Kaiser |first7=Gary W. |last8=Dyke |first8=Gareth J. |author8-link=Gareth J. Dyke |display-authors=3 |year=2013 |title=A Large Accumulation of Avian Eggs from the Late Cretaceous of Patagonia (Argentina) Reveals a Novel Nesting Strategy in Mesozoic Birds |journal=PLOS ONE |location=San Francisco, CA |publisher=PLOS |volume=8 |issue=4 |article-number=e61030 |doi=10.1371/journal.pone.0061030 |pmid=23613776 |pmc=3629076 |bibcode=2013PLoSO...861030F |issn=1932-6203|doi-access=free }}</ref><ref>{{cite journal |last1=Deeming |first1=Denis Charles |last2=Mayr |first2=Gerald |author2-link=Gerald Mayr |date=May 2018 |title=Pelvis morphology suggests that early Mesozoic birds were too heavy to contact incubate their eggs |journal=[[Journal of Evolutionary Biology]] |location=Hoboken, NJ |publisher=Wiley-Blackwell on behalf of the [[European Society for Evolutionary Biology]] |volume=31 |issue=5 |pages=701–709 |doi=10.1111/jeb.13256 |pmid=29485191 |s2cid=3588317 |issn=1010-061X|url=http://eprints.lincoln.ac.uk/id/eprint/31436/13/31436%2031291%20Deeming_et_al-2018-Journal_of_Evolutionary_Biology.pdf |archive-url=https://web.archive.org/web/20200602094641/http://eprints.lincoln.ac.uk/id/eprint/31436/13/31436%2031291%20Deeming_et_al-2018-Journal_of_Evolutionary_Biology.pdf |archive-date=2020-06-02 |url-status=live }}</ref> Both ''Tyrannosaurus'' and ''Troodon'' had juveniles with clear superprecociality and likely occupying different ecological niches than the adults.<ref name="Varrichioetal.02"/> Superprecociality has been inferred for sauropods.<ref>{{cite journal |last1=Myers |first1=Timothy S. |last2=Fiorillo |first2=Anthony R. |year=2009 |title=Evidence for gregarious behavior and age segregation in sauropod dinosaurs |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |location=Amsterdam |publisher=Elsevier |volume=274 |issue=1–2 |pages=96–104 |doi=10.1016/j.palaeo.2009.01.002 |issn=0031-0182|bibcode=2009PPP...274...96M |url=http://doc.rero.ch/record/16633/files/PAL_E962.pdf |archive-url=https://web.archive.org/web/20200529011847/http://doc.rero.ch/record/16633/files/PAL_E962.pdf |archive-date=2020-05-29 |url-status=live }}</ref>

Genital structures are unlikely to fossilize as they lack scales that may allow preservation via pigmentation or residual calcium phosphate salts. In 2021, the best preserved specimen of a dinosaur's [[cloacal vent]] exterior was described for ''Psittacosaurus'', demonstrating lateral swellings similar to crocodylian musk glands used in social displays by both sexes and pigmented regions which could also reflect a signalling function. However, this specimen on its own does not offer enough information to determine whether this dinosaur had sexual signalling functions; it only supports the possibility. Cloacal visual signalling can occur in either males or females in living birds, making it unlikely to be useful to determine sex for extinct dinosaurs.<ref name="cloacal-vent">{{cite journal|doi=10.1016/j.cub.2020.12.039|title=A cloacal opening in a non-avian dinosaur|first1=Jakob|last1=Vinther|first2=Robert|last2=Nicholls|first3=Diane A.|last3=Kelly|journal=Current Biology|volume=31|pages=R1–R3|date=February 22, 2021|issue=4|publisher=Elsevier|pmid=33472049|s2cid=231644183|doi-access=free|bibcode=2021CBio...31.R182V }}</ref>

===Physiology===
{{Main|Physiology of dinosaurs}}

Because both modern crocodilians and birds have four-chambered hearts (albeit modified in crocodilians), it is likely that this is a trait shared by all archosaurs, including all dinosaurs.<ref name=CH04/> While all modern birds have high metabolisms and are [[endotherm]]ic ("warm-blooded"), a vigorous debate has been ongoing since the 1960s regarding how far back in the dinosaur lineage this trait extended. Various researchers have supported dinosaurs as being endothermic, [[ectotherm]]ic ("cold-blooded"), or somewhere in between.<ref name="pontzer2009">{{cite journal |last1=Pontzer |first1=H. |last2=Allen |first2=V. |last3=Hutchinson |first3=J.R. |year=2009 |title=Biomechanics of running indicates endothermy in bipedal dinosaurs |journal=PLOS ONE |volume=4 |issue=11 |article-number=e7783 |doi=10.1371/journal.pone.0007783 |doi-access=free |pmc=2772121 |pmid=19911059 |bibcode=2009PLoSO...4.7783P |issn=1932-6203}}</ref> An emerging consensus among researchers is that, while different lineages of dinosaurs would have had different metabolisms, most of them had higher metabolic rates than other reptiles but lower than living birds and mammals,<ref name="benson2018">{{cite journal |last1=Benson |first1=R.B.J. |year=2018 |title=Dinosaur Macroevolution and Macroecology |journal=Annual Review of Ecology, Evolution, and Systematics |volume=49 |pages=379–408 |doi=10.1146/annurev-ecolsys-110617-062231|s2cid=92837486 |doi-access=free }}</ref> which is termed [[mesotherm]]y by some.<ref name="grady2014">{{cite journal |last1=Grady |first1=J.M. |last2=Enquist |first2=B.J. |last3=Dettweiler-Robinson |first3=E. |last4=Wright |first4=N.A. |last5=Smith |first5=F.A. |year=2014 |title=Evidence for mesothermy in dinosaurs |journal=Science |volume=344 |issue=6189 |pages=1268–1272 |doi=10.1126/science.1253143|pmid=24926017 |bibcode=2014Sci...344.1268G |s2cid=9806780 }}</ref> Evidence from crocodiles and their extinct relatives suggests that such elevated metabolisms could have developed in the earliest archosaurs, which were the common ancestors of dinosaurs and crocodiles.<ref name="legendre2016">{{cite journal |last1=Legendre |first1=L.J. |last2=Guénard |first2=G. |last3=Botha-Brink |first3=J. |last4=Cubo |first4=J. |title=Palaeohistological Evidence for Ancestral High Metabolic Rate in Archosaurs |journal=Systematic Biology |year=2016 |volume=65 |issue=6 |pages=989–996 |doi=10.1093/sysbio/syw033|pmid=27073251 |doi-access=free }}</ref><ref name="seymour2004">{{cite journal |last1=Seymour |first1=R.S. |last2=Bennett-Stamper |first2=C.L. |last3=Johnston |first3=S.D. |last4=Carrier |first4=D.R. |last5=Grigg |first5=G.C. |year=2004 |title=Evidence for endothermic ancestors of crocodiles at the stem of archosaur evolution |journal=Physiological and Biochemical Zoology |volume=77 |issue=6 |pages=1051–1067 |doi=10.1093/sysbio/syw033|pmid=27073251 |doi-access=free }}</ref>

[[File:Pasta-Brontosaurus.jpg|thumb|left|This 1897 restoration of ''[[Brontosaurus]]'' as an aquatic, tail-dragging animal, by [[Charles R. Knight]], typified early views on dinosaur lifestyles.]]
After non-avian dinosaurs were discovered, paleontologists first posited that they were ectothermic. This was used to imply that the ancient dinosaurs were relatively slow, sluggish organisms, even though many modern reptiles are fast and light-footed despite relying on external sources of heat to regulate their body temperature. The idea of dinosaurs as ectothermic remained a prevalent view until [[Robert T. Bakker]], an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968. Bakker specifically used anatomical and ecological evidence to argue that sauropods, which had hitherto been depicted as sprawling aquatic animals with their tails dragging on the ground, were endotherms that lived vigorous, terrestrial lives. In 1972, Bakker expanded on his arguments based on energy requirements and predator-prey ratios. This was one of the seminal results that led to the dinosaur renaissance.<ref name="bakker1968">{{cite journal |last1=Bakker |first1=R.T. |author-link=Robert T. Bakker |year=1968 |title=The Superiority of Dinosaurs |journal=Discovery: Magazine of the Peabody Museum of Natural History |volume=3 |issue=2 |pages=11–22 |issn=0012-3625 |oclc=297237777}}</ref><ref name="bakker1972">{{cite journal |last1=Bakker |first1=R.T. |author-link=Robert T. Bakker |year=1972 |title=Anatomical and Ecological Evidence of Endothermy in Dinosaurs |journal=Nature |volume=238 |issue=5359 |pages=81–85 |doi=10.1038/238081a0|bibcode=1972Natur.238...81B |s2cid=4176132 }}</ref><ref name="taylor2010"/><ref name="parsons2001"/>

One of the greatest contributions to the modern understanding of dinosaur physiology has been [[histology|paleohistology]], the study of microscopic tissue structure in dinosaurs.<ref name="erickson2014">{{cite journal |last1=Erickson |first1=G.M. |year=2014 |title=On dinosaur growth |journal=Annual Review of Earth and Planetary Sciences |volume=42 |issue=1 |pages=675–697 |doi=10.1146/annurev-earth-060313-054858|bibcode=2014AREPS..42..675E }}</ref><ref name="bailleul2019">{{cite journal |last1=Bailleul |first1=A.M. |last2=O'Connor |first2=J. |last3=Schweitzer |first3=M.H. |year=2019 |title=Dinosaur paleohistology: review, trends and new avenues of investigation |journal=PeerJ |volume=7 |article-number=e7764 |doi=10.7717/peerj.7764|pmid=31579624 |pmc=6768056 |bibcode=2019PeerJ...7e7764B |doi-access=free }}</ref> From the 1960s forward, [[Armand de Ricqlès]] suggested that the presence of fibrolamellar bone—bony tissue with an irregular, fibrous texture and filled with blood vessels—was indicative of consistently fast growth and therefore endothermy. Fibrolamellar bone was common in both dinosaurs and pterosaurs,<ref name="dericqles1974">{{cite journal |last1=De Ricqlès |first1=A. |year=1974 |title=Evolution of endothermy: histological evidence |journal=Evolutionary Theory |volume=1 |issue=2 |pages=51–80 |url=http://www.stuartsumida.com/BIOL622/Ricqles1974.pdf |archive-url=https://web.archive.org/web/20210417055907/http://www.stuartsumida.com/BIOL622/Ricqles1974.pdf |archive-date=2021-04-17 |url-status=live}}</ref><ref name="dericqles1980">{{cite book |last1=De Ricqlès |first1=A. |year=1980 |chapter=Tissue structures of dinosaur bone, functional significance and possible relation to dinosaur physiology |editor-last1=Thomas |editor-first1=R.D.K. |editor-last2=Olson |editor-first2=E.C. |title=A Cold Look at the Warm-Blooded Dinosaurs |location=New York |publisher=American Association for the Advancement of Science |pages=103–139}}</ref> though not universally present.<ref name="padian2004">{{cite journal |last1=Padian |first1=K. |last2=Horner |first2=J.R. |last3=de Ricqlès |first3=A. |year=2004 |title=Growth in small dinosaurs and pterosaurs: the evolution of archosaurian growth strategies |journal=Journal of Vertebrate Paleontology |volume=24 |issue=3 |pages=555–571 |doi=10.1671/0272-4634(2004)024[0555:GISDAP]2.0.CO;2 |s2cid=86019906 |url=http://doc.rero.ch/record/15191/files/PAL_E2467.pdf |archive-date=February 4, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20230204094637/https://doc.rero.ch/record/15191/files/PAL_E2467.pdf |url-status=live }}</ref><ref name="desouza2020">{{cite journal |last1=de Souza |first1=G.A. |last2=Bento Soares |first2=M. |last3=Souza Brum |first3=A. |last4=Zucolotto |first4=M. |last5=Sayão |first5=J.M. |last6=Carlos Weinschütz |first6=L. |last7=Kellner |first7=A.W.A. |year=2020 |title=Osteohistology and growth dynamics of the Brazilian noasaurid ''Vespersaurus paranaensis'' Langer et al., 2019 (Theropoda: Abelisauroidea) |journal=PeerJ |volume=8 |article-number=e9771 |doi=10.7717/peerj.9771 |pmid=32983636 |pmc=7500327 |s2cid=221906765 |doi-access=free }}</ref> This has led to a significant body of work in reconstructing [[growth curve (biology)|growth curves]] and modeling the evolution of growth rates across various dinosaur lineages,<ref name="physiologyrefs">For examples of this work conducted on different dinosaur lineages, see

* {{cite journal |last1=Erickson |first1=G.M. |last2=Tumanova |first2=T.A. |year=2000 |title=Growth curve of ''Psittacosaurus mongoliensis'' Osborn (Ceratopsia: Psittacosauridae) inferred from long bone histology |journal=Zoological Journal of the Linnean Society |volume=130 |issue=4 |pages=551–566 |doi=10.1111/j.1096-3642.2000.tb02201.x |s2cid=84241148}}
* {{cite journal |last1=Erickson |first1=G. |last2=Rogers |first2=K. |last3=Yerby |first3=S. |year=2001 |title=Dinosaurian growth patterns and rapid avian growth rates |journal=Nature |volume=412 |issue=429–433 |pages=429–433 |bibcode=2001Natur.412..429E |doi=10.1038/35086558 |pmid=11473315 |s2cid=4319534}}{{Erratum|doi=10.1038/nature16488|pmid=26675731|http://retractionwatch.com/2016/03/01/high-profile-critic-slams-nature-letters-about-dinosaur-growth-following-corrections/ ''Retraction Watch''|checked=yes}}
* {{cite journal |last1=Erickson |first1=G. |last2=Makovicky |first2=P. |last3=Currie |first3=P. |last4=Norell |first4=M.A. |last5=Yerby |first5=S.A. |last6=Brochu |first6=C.A. |year=2004 |title=Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs |url=http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |url-status=live |journal=Nature |volume=430 |issue=7001 |pages=772–775 |bibcode=2004Natur.430..772E |doi=10.1038/nature02699 |pmid=15306807 |s2cid=4404887 |archive-url=https://web.archive.org/web/20200714024211/http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |archive-date=2020-07-14 }}{{Erratum|doi=10.1038/nature16487|pmid=26675726|http://retractionwatch.com/2016/03/01/high-profile-critic-slams-nature-letters-about-dinosaur-growth-following-corrections/ ''Retraction Watch''|checked=yes}}
* {{cite journal |last1=Lehman |first1=T.M. |last2=Woodward |first2=H.N. |year=2008 |title=Modeling growth rates for sauropod dinosaurs |url=http://doc.rero.ch/record/16723/files/PAL_E3766.pdf |journal=Paleobiology |volume=34 |issue=2 |pages=264–281 |doi=10.1666/0094-8373(2008)034[0264:MGRFSD]2.0.CO;2 |s2cid=84163725 |archive-date=February 4, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20230204092325/https://doc.rero.ch/record/16723/files/PAL_E3766.pdf |url-status=live }}
* {{cite journal |last1=Horner |first1=J.R. |last2=de Ricqles |first2=A. |last3=Padian |first3=K. |last4=Scheetz |first4=R.D. |year=2009 |title=Comparative long bone histology and growth of the "hypsilophodontid" dinosaurs ''Orodromeus makelai'', ''Dryosaurus altus'', and ''Tenontosaurus tillettii'' (Ornithischia: Euornithopoda) |journal=Journal of Vertebrate Paleontology |volume=29 |issue=3 |pages=734–747 |bibcode=2009JVPal..29..734H |doi=10.1671/039.029.0312 |s2cid=86277619}}
* {{cite journal |last1=Woodward |first1=H. |last2=Freedman Fowler |first2=E. |last3=Farlow |first3=J. |last4=Horner |first4=J. |year=2015 |title=''Maiasaura'', a model organism for extinct vertebrate population biology: A large sample statistical assessment of growth dynamics and survivorship |journal=Paleobiology |volume=41 |issue=4 |pages=503–527 |bibcode=2015Pbio...41..503W |doi=10.1017/pab.2015.19 |s2cid=85902880}}</ref> which has suggested overall that dinosaurs grew faster than living reptiles.<ref name="bailleul2019"/> Other lines of evidence suggesting endothermy include the presence of feathers and other types of body coverings in many lineages (see {{section link||Feathers}}); more consistent ratios of the isotope [[oxygen-18]] in bony tissue compared to ectotherms, particularly as latitude and thus air temperature varied, which suggests stable internal temperatures<ref name="amiot2006">{{cite journal |last1=Amiot |first1=R. |last2=Lécuyer |first2=C. |last3=Buffetaut |first3=E. |last4=Escarguel |first4=G. |last5=Fluteau |first5=F. |last6=Martineau |first6=F. |year=2006 |title=Oxygen isotopes from biogenic apatites suggest widespread endothermy in Cretaceous dinosaurs |journal=Earth and Planetary Science Letters |volume=246 |issue=1–2 |pages=41–54 |doi=10.1016/j.epsl.2006.04.018|bibcode=2006E&PSL.246...41A |url=http://doc.rero.ch/record/14262/files/PAL_E2159.pdf }}</ref><ref name="amiot2010">{{cite journal |last1=Amiot |first1=R. |last2=Wang |first2=X. |last3=Lécuyer |first3=C. |last4=Buffetaut |first4=E. |last5=Boudad |first5=L. |last6=Cavin |first6=L. |last7=Ding |first7=Z. |last8=Fluteau |first8=F. |last9=Kellner |first9=A.W.A. |last10=Tong |first10=H. |last11=Zhang |first11=F. |year=2010 |title=Oxygen and carbon isotope compositions of middle Cretaceous vertebrates from North Africa and Brazil: ecological and environmental significance |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=297 |issue=2 |pages=439–451 |doi=10.1016/j.palaeo.2010.08.027|bibcode=2010PPP...297..439A }}</ref> (although these ratios can be altered during fossilization<ref name="kolodny1996">{{cite journal |last1=Kolodny |first1=Y. |last2=Luz |first2=B. |last3=Sander |first3=M. |last4=Clemens |first4=W.A. |year=1996 |title=Dinosaur bones: fossils or pseudomorphs? The pitfalls of physiology reconstruction from apatitic fossils |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=126 |issue=1–2 |pages=161–171 |doi=10.1016/S0031-0182(96)00112-5 |bibcode=1996PPP...126..161K |url=http://doc.rero.ch/record/14443/files/PAL_E1627.pdf |archive-date=February 4, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20230204094527/https://doc.rero.ch/record/14443/files/PAL_E1627.pdf |url-status=live }}</ref>); and the discovery of [[South Polar region of the Cretaceous#Dinosaurs|polar dinosaurs]], which lived in Australia, Antarctica, and Alaska when these places would have had cool, temperate climates.<ref name="paul1988">{{cite journal |last1=Paul |first1=G.S. |year=1988 |title=Physiological, migratorial, climatological, geophysical, survival, and evolutionary implications of Cretaceous polar dinosaurs |journal=Journal of Paleontology |volume=62 |issue=4 |pages=640–652 |jstor=1305468|ref=none}}</ref><ref name="clemens1993">{{cite journal |last1=Clemens |first1=W.A. |last2=Nelms |first2=L.G. |year=1993 |title=Paleoecological implications of Alaskan terrestrial vertebrate fauna in latest Cretaceous time at high paleolatitudes |journal=Geology |volume=21 |issue=6 |pages=503–506 |doi=10.1130/0091-7613(1993)021<0503:PIOATV>2.3.CO;2|bibcode=1993Geo....21..503C }}</ref><ref name="rich2002">{{cite journal |last1=Rich |first1=T.H. |last2=Vickers-Rich |first2=P. |last3=Gangloff |first3=R.A. |year=2002 |title=Polar dinosaurs |journal=Science |volume=295 |issue=5557 |pages=979–980 |doi=10.1126/science.1068920|pmid=11834803 |s2cid=28065814 }}</ref><ref name="buffetaut2004">{{cite journal |last1=Buffetaut |first1=E. |year=2004 |title=Polar dinosaurs and the question of dinosaur extinction: a brief review |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=214 |issue=3 |pages=225–231 |doi=10.1016/j.palaeo.2004.02.050|url=http://doc.rero.ch/record/15383/files/PAL_E2734.pdf |archive-url=https://web.archive.org/web/20200608120307/http://doc.rero.ch/record/15383/files/PAL_E2734.pdf |archive-date=2020-06-08 |url-status=live }}</ref>

[[File:Dino bird h.jpg|thumb|Comparison between the [[air sac]]s of an [[abelisaur]] and a bird]]
In saurischian dinosaurs, higher metabolisms were supported by the evolution of the avian respiratory system, characterized by an extensive system of [[air sac]]s that extended the lungs and invaded many of the bones in the skeleton, making them hollow.<ref name=Sereno2008/> Such respiratory systems, which may have appeared in the earliest saurischians,<ref name="oconnor2009">{{cite journal |last1=O'Connor |first1=P.M. |year=2009 |title=Evolution of archosaurian body plans: skeletal adaptations of an air-sac-based breathing apparatus in birds and other archosaurs |journal=Journal of Experimental Zoology Part A: Ecological Genetics and Physiology |volume=311 |issue=8 |pages=629–646 |doi=10.1002/jez.548|pmid=19492308 |bibcode=2009JEZA..311..629O }}</ref> would have provided them with more oxygen compared to a mammal of similar size, while also having a larger resting [[tidal volume]] and requiring a lower breathing frequency, which would have allowed them to sustain higher activity levels.<ref name="sander2011"/> The rapid airflow would also have been an effective cooling mechanism, which in conjunction with a lower metabolic rate<ref name="eagle2011">{{cite journal |last1=Eagle |first1=R.A. |last2=Tütken |first2=T. |last3=Martin |first3=T.S. |last4=Tripati |first4=A.K. |last5=Fricke |first5=H.C. |last6=Connely |first6=M. |last7=Cifelli |first7=R.L. |last8=Eiler |first8=J.M. |year=2011 |title=Dinosaur body temperatures determined from isotopic (<sup>13</sup>C-<sup>18</sup>O) ordering in fossil biominerals |journal=Science |volume=333 |issue=6041 |pages=443–445 |pmid=21700837 |doi=10.1126/science.1206196 |bibcode=2011Sci...333..443E |s2cid=206534244}}</ref> would have prevented large sauropods from overheating. These traits may have enabled sauropods to grow quickly to gigantic sizes.<ref name="wedel2003">{{cite journal |last1=Wedel |first1=M.J. |year=2003 |title=Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs |journal=Paleobiology |volume=29 |issue=2 |pages=243–255 |doi=10.1017/S0094837300018091 |bibcode=2003Pbio...29..243W |url=http://doc.rero.ch/record/14872/files/PAL_E2010.pdf |archive-date=May 18, 2023 |access-date=January 3, 2024 |archive-url=https://web.archive.org/web/20230518003816/https://doc.rero.ch/record/14872/files/PAL_E2010.pdf |url-status=live }}</ref><ref name="perry2009">{{cite journal |last1=Perry |first1=S.F. |last2=Christian |first2=A. |last3=Breuer |first3=T. |last4=Pajor |first4=N. |last5=Codd |first5=J.R. |year=2009 |title=Implications of an avian-style respiratory system for gigantism in sauropod dinosaurs |journal=Journal of Experimental Zoology Part A: Ecological Genetics and Physiology |volume=311 |issue=8 |pages=600–610 |doi=10.1002/jez.517 |pmid=19189317|bibcode=2009JEZA..311..600P }}</ref> Sauropods may also have benefitted from their size—their small surface area to volume ratio meant that they would have been able to thermoregulate more easily, a phenomenon termed [[gigantothermy]].<ref name="sander2011"/><ref name="alexander1998">{{cite journal |last1=Alexander |first1=R.M. |year=1998 |title=All-time giants: the largest animals and their problems |journal=Palaeontology |volume=41 |pages=1231–1245 |url=https://www.palass.org/publications/palaeontology-journal/archive/41/6/article_pp1231-1245 |archive-date=September 27, 2016 |access-date=January 2, 2021 |archive-url=https://web.archive.org/web/20160927060250/https://www.palass.org/publications/palaeontology-journal/archive/41/6/article_pp1231-1245 |url-status=live }}</ref>

Like other reptiles, dinosaurs are primarily [[uricotelic]], that is, their [[kidney]]s extract nitrogenous wastes from their bloodstream and excrete it as [[uric acid]] instead of [[urea]] or [[ammonia]] via the ureters into the intestine. This would have helped them to conserve water.<ref name="benson2018"/> In most living species, uric acid is excreted along with feces as a semisolid waste.<ref name="tsahar2005">{{cite journal |last1=Tsahar |first1=E. |last2=Martínez del Rio |first2=C. |last3=Izhaki |first3=I. |last4=Arad |first4=Z. |year=2005 |title=Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores |journal=[[The Journal of Experimental Biology]] |volume=208 |issue=6 |pages=1025–1034 |url= https://jeb.biologists.org/content/jexbio/208/6/1025.full.pdf |url-status=live |doi=10.1242/jeb.01495 |issn=0022-0949 |pmid=15767304 |bibcode=2005JExpB.208.1025T |s2cid=18540594 |archive-url=https://web.archive.org/web/20191017110333/https://jeb.biologists.org/content/jexbio/208/6/1025.full.pdf |archive-date=October 17, 2019 |access-date=October 31, 2019}}</ref><ref name="skadhauge2003">{{cite journal |last1=Skadhauge |first1=E. |last2=Erlwanger |first2=K.H. |last3=Ruziwa |first3=S.D. |last4=Dantzer |first4=V. |last5=Elbrønd |first5=V.S. |last6=Chamunorwa |first6=J.P. |year=2003 |title=Does the ostrich (''Struthio camelus'') coprodeum have the electrophysiological properties and microstructure of other birds? |journal=[[Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology]] |volume=134 |issue=4 |pages=749–755 |doi=10.1016/S1095-6433(03)00006-0 |issn=1095-6433 |pmid=12814783}}</ref> However, at least some modern birds (such as [[hummingbird]]s) can be facultatively [[ammonotelic]], excreting most of the nitrogenous wastes as ammonia.<ref name="preest1997">{{cite journal |last1=Preest |first1=M.R. |last2=Beuchat |first2=C.A. |year=1997 |title=Ammonia excretion by hummingbirds |journal=Nature |volume=386 |issue=6625 |pages=561–562 |bibcode=1997Natur.386..561P |doi=10.1038/386561a0 |s2cid=4372695 |issn=0028-0836}}</ref> This material, as well as the output of the intestines, emerges from the [[cloaca]].<ref name="mora1965">{{cite journal |last1=Mora |first1=J. |last2=Martuscelli |first2=J. |last3=Ortiz Pineda |first3=J. |last4=Soberon |first4=G. |year=1965 |title=The Regulation of Urea-Biosynthesis Enzymes in Vertebrates |journal=[[Biochemical Journal]] |volume=96 |issue=1 |pages=28–35 |issn=0264-6021 |doi=10.1042/bj0960028 |pmc=1206904 |pmid=14343146}}</ref><ref name="packard1966">{{cite journal |last=Packard |first=G.C. |year=1966 |title=The Influence of Ambient Temperature and Aridity on Modes of Reproduction and Excretion of Amniote Vertebrates |journal=The American Naturalist |volume=100 |issue=916 |pages=667–682 |doi=10.1086/282459 |issn=0003-0147 |jstor=2459303 |bibcode=1966ANat..100..667P |s2cid=85424175}}</ref> In addition, many species regurgitate [[Pellet (ornithology)|pellets]],<ref name="balgooyen1971">{{cite journal |last=Balgooyen |first=T.G. |year=1971 |title=Pellet Regurgitation by Captive Sparrow Hawks (''Falco sparverius'') |journal=[[The Condor (journal)|Condor]] |volume=73 |issue=3 |pages=382–385 |jstor=1365774 |url=https://sora.unm.edu/sites/default/files/journals/condor/v073n03/p0382-p0385.pdf |doi=10.2307/1365774 |archive-url=https://web.archive.org/web/20190404001957/https://sora.unm.edu/sites/default/files/journals/condor/v073n03/p0382-p0385.pdf |archive-date=April 4, 2019 |access-date=October 30, 2019}}</ref> and fossil pellets are known as early as the Jurassic from ''[[Anchiornis]]''.<ref name="xu2018">{{cite journal |last1=Xu |first1=X. |last2=Li |first2=F. |last3=Wang |first3=Y. |last4=Sullivan |first4=C. |last5=Zhang |first5=F. |last6=Zhang |first6=X. |last7=Sullivan |first7=C. |last8=Wang |first8=X. |last9=Zheng |first9=X. |year=2018 |title=Exceptional dinosaur fossils reveal early origin of avian-style digestion |journal=Scientific Reports |volume=8 |issue=1 |page=14217 |doi=10.1038/s41598-018-32202-x |pmid=30242170 |issn=2045-2322 |pmc=6155034 |bibcode=2018NatSR...814217Z}}</ref>

{{anchor|intelligence}}The size and shape of the brain can be partly reconstructed based on the surrounding bones. In 1896, Marsh calculated ratios between brain weight and body weight of seven species of dinosaurs, showing that the brain of dinosaurs was proportionally smaller than in today's crocodiles, and that the brain of ''Stegosaurus'' was smaller than in any living land vertebrate. This contributed to the widespread public notion of dinosaurs as being sluggish and extraordinarily stupid. Harry Jerison, in 1973, showed that proportionally smaller brains are expected at larger body sizes, and that brain size in dinosaurs was not smaller than expected when compared to living reptiles.<ref name="russell1997"/> Later research showed that relative brain size progressively increased during the evolution of theropods, with the highest intelligence – comparable to that of modern birds – calculated for the troodontid ''Troodon''.<ref name="brusatte2012"/>

==Origin of birds==
{{Main|Origin of birds}}

The possibility that dinosaurs were the ancestors of birds was first suggested in 1868 by [[Thomas Henry Huxley]].<ref name=huxley1868/> After the work of [[Gerhard Heilmann]] in the early 20th century, the [[Scientific theory|theory]] of birds as dinosaur descendants was abandoned in favor of the idea of them being descendants of generalized [[Thecodontia|thecodonts]], with the key piece of evidence being the supposed lack of [[clavicle]]s in dinosaurs.<ref name=heilmann/> However, as later discoveries showed, clavicles (or a single fused [[furcula|wishbone]], which derived from separate clavicles) were not actually absent;<ref name=KP04/> they had been found as early as 1924 in ''[[Oviraptor]]'', but misidentified as an [[interclavicle]].<ref name=HO24/> In the 1970s, John Ostrom revived the dinosaur–bird theory,<ref name=ostrom1973/> which gained momentum in the coming decades with the advent of cladistic analysis,<ref name=gauthier1986/> and a great increase in the discovery of small theropods and early birds.<ref name=TRHJ00/> Of particular note have been the fossils of the Jehol Biota, where a variety of theropods and early birds have been found, often with feathers of some type.<ref name=KP04/><ref name="NYT-20161208"/> Birds share over a hundred distinct anatomical features with other theropod dinosaurs.<ref name=Mayretal2005/> They are most closely allied with maniraptoran coelurosaurs.<ref name=KP04/> A minority of scientists, most notably [[Alan Feduccia]] and [[Larry Martin]], have proposed other evolutionary paths, including revised versions of Heilmann's basal archosaur proposal,<ref name=martin2004/> or that maniraptoran theropods are the ancestors of birds but themselves are not dinosaurs, only [[convergent evolution|convergent]] with dinosaurs.<ref name=AF02/>

===Feathers===
{{Main|Feathered dinosaurs}}

[[File:Feathered non-avian Maniraptora.jpg|thumb|Various feathered non-avian dinosaurs, including ''[[Archaeopteryx]]'', ''[[Anchiornis]]'', ''[[Microraptor]]'' and ''[[Zhenyuanlong]]'']]
Feathers are one of the most recognizable characteristics of modern birds, and a trait that was also shared by several non-avian dinosaurs. Based on the current distribution of fossil evidence, it appears that feathers were an ancestral dinosaurian trait, though one that may have been selectively lost in some species.<ref name=switeknature>{{cite journal |url=https://www.nature.com/articles/nature.2012.10933 |title=Rise of the fuzzy dinosaurs |last1=Switek |first1=Brian |date=July 2, 2012 |department=News |journal=Nature |publisher=Nature Research |location=London |doi=10.1038/nature.2012.10933 |s2cid=123219913 |issn=0028-0836 |access-date=January 1, 2019 |archive-date=April 13, 2020 |archive-url=https://web.archive.org/web/20200413155956/https://www.nature.com/articles/nature.2012.10933 |url-status=live |url-access=subscription }}</ref> Direct fossil evidence of feathers or feather-like structures has been discovered in a diverse array of species in many non-avian dinosaur groups,<ref name="NYT-20161208" /> both among saurischians and ornithischians. Simple, branched, feather-like structures are known from [[Heterodontosauridae|heterodontosaurids]], primitive [[neornithischia]]ns,<ref name="Godefroit2014">{{cite journal | last1 = Godefroit | first1 = P. | last2 = Sinitsa | first2 = S.M. | last3 = Dhouailly | first3 = D. | last4 = Bolotsky | first4 = Y.L. | last5 = Sizov | first5 = A.V. | last6 = McNamara | first6 = M.E. | last7 = Benton | first7 = M.J. | last8 = Spagna | first8 = P. | year = 2014 | title = A Jurassic ornithischian dinosaur from Siberia with both feathers and scales | url = http://palaeo.gly.bris.ac.uk/Benton/reprints/2014Kulinda.pdf | journal = Science | volume = 345 | issue = 6195 | pages = 451–455 | doi = 10.1126/science.1253351 | pmid = 25061209 | bibcode = 2014Sci...345..451G | hdl = 1983/a7ae6dfb-55bf-4ca4-bd8b-a5ea5f323103 | s2cid = 206556907 | access-date = July 27, 2016 | archive-url = https://web.archive.org/web/20190209232112/http://palaeo.gly.bris.ac.uk/Benton/reprints/2014Kulinda.pdf | archive-date = February 9, 2019 }}</ref> and theropods,<ref name=Xuetal2004/> and primitive ceratopsians. Evidence for true, vaned feathers similar to the flight feathers of modern birds has been found only in the theropod subgroup Maniraptora, which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds.<ref name=KP04/><ref name=GC06/> Feather-like structures known as [[Pterosaur#Pycnofibers|pycnofibre]]s have also been found in pterosaurs.<ref name=kellneretal2009>{{cite journal |last1=Kellner |first1=Alexander W. A. |author1-link=Alexander Kellner |last2=Wang |first2=Xiaolin |last3=Tischlinger |first3=Helmut |last4=Campos |first4=Diogenes de Almeida |last5=Hone |first5=David W. E. |last6=Meng |first6=Xi |display-authors=3 |year=2010 |title=The soft tissue of ''Jeholopterus'' (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane |journal=Proceedings of the Royal Society B |location=London |publisher=Royal Society |volume=277 |issue=1679 |pages=321–329 |doi=10.1098/rspb.2009.0846 |issn=0962-8452 |pmc=2842671 |pmid=19656798}}</ref>

However, researchers do not agree on whether these structures share a common origin between lineages (i.e., they are [[homology (biology)|homologous]]),<ref name="mayr2016">{{cite journal |last1=Mayr |first1=G. |last2=Pittman |first2=M. |last3=Saitta |first3=E. |last4=Kaye |first4=T.G. |last5=Vinther |first5=J. |year=2016 |title=Structure and homology of ''Psittacosaurus'' tail bristles |journal=Palaeontology |volume=59 |issue=6 |pages=793–802 |doi=10.1111/pala.12257|bibcode=2016Palgy..59..793M |hdl=1983/029c668f-08b9-45f6-a0c5-30ce9256e593 |s2cid=89156313|url=https://research-information.bris.ac.uk/en/publications/029c668f-08b9-45f6-a0c5-30ce9256e593 |hdl-access=free }}</ref><ref name="benton2019"/> or if they were the result of widespread experimentation with skin coverings among ornithodirans.<ref name="barrett2015">{{cite journal |last1=Barrett |first1=P.M. |last2=Evans |first2=D.C. |last3=Campione |first3=N.E. |year=2015 |title=Evolution of dinosaur epidermal structures |journal=Biology Letters |volume=11 |issue=6 |article-number=20150229 |doi=10.1098/rsbl.2015.0229 |pmc=4528472 |pmid=26041865}}</ref> If the former is the case, filaments may have been common in the ornithodiran lineage and evolved before the appearance of dinosaurs themselves.<ref name=switeknature/> Research into the genetics of [[American alligator]]s has revealed that crocodylian [[scute]]s do possess feather-keratins during embryonic development, but these keratins are not expressed by the animals before hatching.<ref name=AlibL2006>{{cite journal |last1=Alibardi |first1=Lorenzo |last2=Knapp |first2=Loren W. |last3=Sawyer |first3=Roger H. |year=2006 |title=Beta-keratin localization in developing alligator scales and feathers in relation to the development and evolution of feathers |journal=Journal of Submicroscopic Cytology and Pathology |location=[[Siena]] |publisher=Nuova Immagine Editrice |volume=38 |issue=2–3 |pages=175–192 |issn=1122-9497 |pmid=17784647}}</ref> The description of feathered dinosaurs has not been without controversy in general; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that some purported feather-like fossils are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' skin,<ref name=TLS03/><ref name=FLH05/><ref name=LSFX07/> and that maniraptoran dinosaurs with vaned feathers were not actually dinosaurs, but convergent with dinosaurs.<ref name=AF02/><ref name=FLH05/> However, their views have for the most part not been accepted by other researchers, to the point that the scientific nature of Feduccia's proposals has been questioned.<ref name=Prum2003/>

''[[Archaeopteryx]]'' was the first fossil found that revealed a potential connection between dinosaurs and birds. It is considered a [[transitional fossil]], in that it displays features of both groups. Brought to light just two years after [[Charles Darwin]]'s seminal ''[[On the Origin of Species]]'' (1859), its discovery spurred the nascent debate between proponents of [[evolutionary biology]] and [[creationism]]. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for the small theropod ''[[Compsognathus]]''.<ref name=PW88/> Since the 1990s, a number of additional feathered dinosaurs have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. Many of these specimens were unearthed in the [[lagerstätten]] of the Jehol Biota.<ref name="benton2019">{{cite journal |last1=Benton |first1=M.J. |last2=Dhouailly |first2=D. |last3=Jiang |first3=B. |last4=McNamara |first4=M. |year=2019 |title=The Early Origin of Feathers |journal=Trends in Ecology & Evolution |volume=34 |issue=9 |pages=856–869 |doi=10.1016/j.tree.2019.04.018|pmid=31164250 |bibcode=2019TEcoE..34..856B |hdl=10468/8068 |s2cid=174811556 |hdl-access=free }}</ref> If feather-like structures were indeed widely present among non-avian dinosaurs, the lack of abundant fossil evidence for them may be due to the fact that delicate features like skin and feathers are seldom preserved by fossilization and thus often absent from the fossil record.<ref name="Schweitzeretal1999">{{cite journal |last1=Schweitzer |first1=Mary H. |last2=Watt |first2=J.A. |last3=Avci |first3=R. |last4=Knapp |first4=L. |last5=Chiappe |first5=L. |last6=Norell |first6=M. |last7=Marshall |first7=M. |display-authors=3 |year=1999 |title=Beta-keratin specific immunological reactivity in feather-like structures of the Cretaceous Alvarezsaurid, ''Shuvuuia deserti'' |journal=[[Journal of Experimental Zoology|Journal of Experimental Zoology Part B]] |location=Hoboken, NJ |publisher=Wiley-Blackwell |volume=285 |issue=2 |pages=146–157 |pmid=10440726 |doi=10.1002/(SICI)1097-010X(19990815)285:2<146::AID-JEZ7>3.0.CO;2-A |bibcode=1999JEZ...285..146S |issn=1552-5007}}</ref>

===Skeleton===
Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent another important line of evidence for paleontologists. Areas of the skeleton with important similarities include the neck, pubis, [[wrist]] (semi-lunate [[carpal]]), arm and [[Shoulder girdle|pectoral girdle]], furcula (wishbone), and [[Keel (bird anatomy)|breast bone]]. Comparison of bird and dinosaur skeletons through cladistic analysis strengthens the case for the link.<ref name=archaeopteryxucmp>{{cite web |url=https://ucmp.berkeley.edu/diapsids/birds/archaeopteryx.html |last=<!--Staff writer(s); no by-line.--> |title=''Archaeopteryx'': An Early Bird |publisher=University of California Museum of Paleontology |location=Berkeley |access-date=October 30, 2019 |archive-date=February 3, 2021 |archive-url=https://web.archive.org/web/20210203232245/https://ucmp.berkeley.edu/diapsids/birds/archaeopteryx.html |url-status=live }}</ref>

===Soft anatomy===
[[File:Pneumatopores on the left ilium of the theropod Aerosteon riocoloradensis.jpg|thumb|Pneumatopores on the left [[ilium (bone)|ilium]] of ''[[Aerosteon|Aerosteon riocoloradensis]]'']]
Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to a 2005 investigation led by Patrick M. O'Connor. The lungs of theropod dinosaurs (carnivores that walked on two legs and had bird-like feet) likely pumped air into hollow sacs in their skeletons, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds", O'Connor said.<ref name=OConnorClaessens2005/><ref>{{Cite journal |last1=O'Connor |first1=Patrick M. |last2=Claessens |first2=Leon P. A. M. |date=July 2005 |title=Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs |url=https://www.nature.com/articles/nature03716 |journal=Nature |language=en |volume=436 |issue=7048 |pages=253–256 |doi=10.1038/nature03716 |pmid=16015329 |bibcode=2005Natur.436..253O |issn=0028-0836 |archive-date=December 25, 2024 |access-date=December 25, 2024 |archive-url=https://web.archive.org/web/20241225213025/https://www.nature.com/articles/nature03716 |url-status=live |url-access=subscription }}</ref> In 2008, scientists described ''[[Aerosteon|Aerosteon riocoloradensis]]'', the skeleton of which supplies the strongest evidence to date of a dinosaur with a bird-like breathing system. [[CT scan]]ning of ''Aerosteon'''s fossil bones revealed evidence for the existence of air sacs within the animal's body cavity.<ref name=Sereno2008/><ref name=newswise2/>

===Behavioral evidence===
Fossils of the troodonts ''[[Mei long|Mei]]'' and ''[[Sinornithoides]]'' demonstrate that some dinosaurs slept with their heads tucked under their arms.<ref name=XUNorell2004/> This behavior, which may have helped to keep the head warm, is also characteristic of modern birds. Several [[Deinonychosauria|deinonychosaur]] and oviraptorosaur specimens have also been found preserved on top of their nests, likely brooding in a bird-like manner.<ref name="norell1995">{{cite journal |last1=Norell |first1=Mark A. |last2=Clark |first2=James M. |last3=Chiappe |first3=Luis M. |last4=Dashzeveg |first4=Demberelyin |display-authors=3 |year=1995 |title=A nesting dinosaur |journal=Nature |location=London |publisher=Nature Research |volume=378 |issue=6559 |pages=774–776 |bibcode=1995Natur.378..774N |doi=10.1038/378774a0 |s2cid=4245228 |issn=0028-0836}}</ref> The ratio between egg volume and body mass of adults among these dinosaurs suggest that the eggs were primarily brooded by the male and that the young were highly precocial, similar to many modern ground-dwelling birds.<ref name=Varricchioetal2008>{{cite journal |last1=Varricchio |first1=David J. |last2=Moore |first2=Jason R. |last3=Erickson |first3=Gregory M. |author3-link=Gregory M. Erickson |last4=Norell |first4=Mark A. |last5=Jackson |first5=Frankie D. |last6=Borkowski |first6=John J. |display-authors=3 |year=2008 |title=Avian Paternal Care Had Dinosaur Origin |journal=Science |location=Washington, D.C. |publisher=American Association for the Advancement of Science |volume=322 |issue=5909 |pages=1826–1828 |bibcode=2008Sci...322.1826V |doi=10.1126/science.1163245 |issn=0036-8075 |pmid=19095938|s2cid=8718747 |doi-access=free }}</ref>

Some dinosaurs are known to have used [[gizzard]] stones like modern birds. These stones are swallowed by animals to aid digestion and break down food and hard fibers once they enter the stomach. When found in association with fossils, gizzard stones are called gastroliths.<ref name=wings2007/>

==Extinction of major groups==
{{Main|Cretaceous–Paleogene extinction event}}

All non-avian dinosaurs and most lineages of birds<ref name="longrich2011">{{cite journal |last1=Longrich |first1=N.R. |last2=Tokaryk |first2=T. |last3=Field |first3=D.J. |year=2011 |title=Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary |journal=Proceedings of the National Academy of Sciences |volume=108 |issue=37 |pages=15253–15257 |doi=10.1073/pnas.1110395108|pmid=21914849 |pmc=3174646 |bibcode=2011PNAS..10815253L |doi-access=free }}</ref> became extinct in a [[extinction event|mass extinction event]], called the [[Cretaceous–Paleogene extinction event|Cretaceous–Paleogene (K-Pg) extinction event]], at the end of the Cretaceous period. Above the [[Cretaceous–Paleogene boundary]], which has been dated to 66.038 ± 0.025 million years ago,<ref name="renne2013">{{cite journal |last1=Renne |first1=P.R. |last2=Deino |first2=A.L. |last3=Hilgen |first3=F.J. |last4=Kuiper |first4=K.F. |last5=Mark |first5=D.F. |last6=Mitchell |first6=W.S. |last7=Morgan |first7=L.E. |last8=Mundil |first8=R. |last9=Smit |first9=J. |year=2013 |title=Time scales of critical events around the Cretaceous-Paleogene boundary |journal=Science |volume=339 |issue=6120 |pages=684–687 |doi=10.1126/science.1230492|pmid=23393261 |bibcode=2013Sci...339..684R |s2cid=6112274 }}</ref> fossils of non-avian dinosaurs disappear abruptly; the absence of dinosaur fossils was historically used to assign rocks to the ensuing Cenozoic. The nature of the event that caused this mass extinction has been extensively studied since the 1970s, leading to the development of two mechanisms that are thought to have played major roles: an extraterrestrial [[impact event]] in the [[Yucatán Peninsula]], along with [[flood basalt]] volcanism in [[India]]. However, the specific mechanisms of the extinction event and the extent of its effects on dinosaurs are still areas of ongoing research.<ref name="brusatte2014">{{cite journal |last1=Brusatte |first1=S.L. |last2=Butler |first2=R.J. |last3=Barrett |first3=P.M. |last4=Carrano |first4=M.T. |last5=Evans |first5=D.C. |last6=Lloyd |first6=G.T. |last7=Mannion |first7=P.D. |last8=Norell |first8=M.A. |last9=Peppe |first9=D.J. |last10=Upchurch |first10=P. |last11=Williamson |first11=T.E. |year=2015 |title=The extinction of the dinosaurs |journal=Biological Reviews |volume=90 |issue=2 |pages=628–642 |doi=10.1111/brv.12128|pmid=25065505 |hdl=20.500.11820/176e5907-26ec-4959-867f-0f2e52335f88 |s2cid=115134484 |url=https://www.research.ed.ac.uk/en/publications/176e5907-26ec-4959-867f-0f2e52335f88 |doi-access=free |hdl-access=free }}</ref> Alongside dinosaurs, many other groups of animals became extinct: pterosaurs, marine reptiles such as mosasaurs and plesiosaurs, several groups of mammals, [[ammonoidea|ammonites]] ([[nautilus]]-like [[Mollusca|mollusks]]), [[rudist]]s ([[reef]]-building [[bivalvia|bivalves]]), and various groups of marine plankton.<ref name="macleod1997"/><ref name="archibald1982"/> In all, approximately 47% of genera and 76% of species on Earth became extinct during the K-Pg extinction event.<ref name="jablonski1991">{{cite journal |last1=Jablonski |first1=D. |year=1991 |title=Extinctions: a paleontological perspective |journal=Science |volume=253 |issue=5021 |pages=754–757 |doi=10.1126/science.253.5021.754|pmid=17835491 |bibcode=1991Sci...253..754J }}</ref> The relatively large size of most dinosaurs and the low diversity of small-bodied dinosaur species at the end of the Cretaceous may have contributed to their extinction;<ref>{{cite journal |last1=Longrich |first1=N.R. |last2=Bhullar |first2=B.-A. S. |last3=Gauthier |first3=J.A. |year=2012 |title=Mass extinction of lizards and snakes at the Cretaceous–Paleogene boundary |journal=Proceedings of the National Academy of Sciences |volume=109 |issue=52 |pages=21396–21401 |bibcode=2012PNAS..10921396L |doi=10.1073/pnas.1211526110 |issn=0027-8424 |pmc=3535637 |pmid=23236177|doi-access=free }}</ref> the extinction of the bird lineages that did not survive may also have been caused by a dependence on forest habitats or a lack of adaptations to [[seed predation|eating seeds]] for survival.<ref name="field2018">{{cite journal |last1=Field |first1=D.J. |last2=Bercovici |first2=A. |last3=Berv |first3=J.S. |last4=Dunn |first4=R. |last5=Fastovsky |first5=D.E. |last6=Lyson |first6=T.R. |last7=Vajda |first7=V. |last8=Gauthier |first8=J.A. |year=2018 |title=Early evolution of modern birds structured by global forest collapse at the end-Cretaceous mass extinction |journal=Current Biology |volume=28 |issue=11 |pages=1825–1831 |doi=10.1016/j.cub.2018.04.062|pmid=29804807 |s2cid=44075214 |doi-access=free |bibcode=2018CBio...28E1825F }}</ref><ref name="larson2016">{{cite journal |last1=Larson |first1=D.W. |last2=Brown |first2=C.M. |last3=Evans |first3=D.C. |year=2016 |title=Dental disparity and ecological stability in bird-like dinosaurs prior to the end-Cretaceous mass extinction |journal=Current Biology |volume=26 |issue=10 |pages=1325–1333 |doi=10.1016/j.cub.2016.03.039|pmid=27112293 |s2cid=3937001 |doi-access=free |bibcode=2016CBio...26.1325L }}</ref>

===Pre-extinction diversity===
Just before the K-Pg extinction event, the number of non-avian dinosaur species that existed globally has been estimated at between 628 and 1078.<ref name="leloeuff2012">{{cite journal |last=Le Loeuff |first=J. |year=2012 |title=Paleobiogeography and biodiversity of Late Maastrichtian dinosaurs: how many dinosaur species went extinct at the Cretaceous-Tertiary boundary? |journal=[[Bulletin de la Société Géologique de France]] |volume=183 |issue=6 |pages=547–559 |doi=10.2113/gssgfbull.183.6.547 |issn=0037-9409}}</ref> It remains uncertain whether the diversity of dinosaurs was in gradual decline before the K-Pg extinction event, or whether dinosaurs were actually thriving prior to the extinction. Rock formations from the [[Maastrichtian]] epoch, which directly preceded the extinction, have been found to have lower diversity than the preceding [[Campanian]] epoch, which led to the prevailing view of a long-term decline in diversity.<ref name="macleod1997"/><ref name="archibald1982">{{cite journal |last1=Archibald |first1=J.D. |last2=Clemens |first2=W.A. |year=1982 |title=Late Cretaceous Extinctions |journal=American Scientist |volume=70 |issue=4 |pages=377–385 |jstor=27851545|bibcode=1982AmSci..70..377A }}</ref><ref name="carpenter1983">{{cite journal |last1=Carpenter |first1=K. |year=1983 |title=Evidence suggesting gradual extinction of latest Cretaceous dinosaurs |journal=Naturwissenschaften |volume=70 |issue=12 |pages=611–612 |doi=10.1007/BF00377404 |bibcode=1983NW.....70..611C |s2cid=20078285 }}</ref> However, these comparisons did not account either for varying [[preservation potential]] between rock units or for different extents of exploration and excavation.<ref name="brusatte2014"/> In 1984, [[Dale Russell]] carried out an analysis to account for these biases, and found no evidence of a decline;<ref name="russell1984">{{cite journal |last1=Russell |first1=D.A. |year=1984 |title=The gradual decline of the dinosaurs—fact or fallacy? |journal=Nature |volume=307 |issue=5949 |pages=360–361 |doi=10.1038/307360a0|bibcode=1984Natur.307..360R |s2cid=4269426 }}</ref> another analysis by David Fastovsky and colleagues in 2004 even showed that dinosaur diversity continually increased until the extinction,<ref name="fastovsky2004">{{cite journal |last1=Fastovsky |first1=D.E. |last2=Huang |first2=Y. |last3=Hsu |first3=J. |last4=Martin-McNaughton |first4=J. |last5=Sheehan |first5=P.M. |last6=Weishampel |first6=D.B. |year=2004 |title=Shape of Mesozoic dinosaur richness |journal=Geology |volume=32 |issue=10 |pages=877–880 |doi=10.1130/G20695.1 |bibcode=2004Geo....32..877F |url=http://doc.rero.ch/record/14984/files/PAL_E2134.pdf |archive-date=February 4, 2023 |access-date=January 26, 2023 |archive-url=https://web.archive.org/web/20230204093851/https://doc.rero.ch/record/14984/files/PAL_E2134.pdf |url-status=live }}</ref> but this analysis has been rebutted.<ref name="sullivan2006">{{cite book |last1=Sullivan |first1=R.M. |year=2006 |chapter=The shape of Mesozoic dinosaur richness: a reassessment |editor-last1=Lucas |editor-first1=S.G. |editor-last2=Sullivan |editor-first2=R.M. |title=Late Cretaceous vertebrates from the Western Interior |series=New Mexico Museum of Natural History and Science Bulletin |volume=35 |pages=403–405 |chapter-url=https://books.google.com/books?id=rCDYCQAAQBAJ&pg=PA403}}</ref> Since then, different approaches based on statistics and mathematical models have variously supported either a sudden extinction<ref name="brusatte2014"/><ref name="leloeuff2012"/><ref name="chiarenza2019">{{cite journal |last1=Chiarenza |first1=A.A. |last2=Mannion |first2=P.D. |last3=Lunt |first3=D.J. |last4=Farnsworth |first4=A. |last5=Jones |first5=L.A. |last6=Kelland |first6=S.J. |last7=Allison |first7=P.A. |year=2019 |title=Ecological niche modelling does not support climatically-driven dinosaur diversity decline before the Cretaceous/Paleogene mass extinction |journal=Nature Communications |volume=10 |issue=1 |pages=1–14 |doi=10.1038/s41467-019-08997-2|pmid=30842410 |pmc=6403247 |bibcode=2019NatCo..10.1091C }}</ref> or a gradual decline.<ref name="lloyd2011">{{cite journal |last1=Lloyd |first1=G.T. |year=2012 |title=A refined modelling approach to assess the influence of sampling on palaeobiodiversity curves: new support for declining Cretaceous dinosaur richness |journal=Biology Letters |volume=8 |issue=1 |pages=123–126 |doi=10.1098/rsbl.2011.0210|pmid=21508029 |pmc=3259943 |s2cid=1376734 }}</ref><ref name="sakamoto2016">{{cite journal |last1=Sakamoto |first1=M. |last2=Benton |first2=M.J. |last3=Venditti |first3=C. |year=2016 |title=Dinosaurs in decline tens of millions of years before their final extinction |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=18 |pages=5036–5040 |doi=10.1073/pnas.1521478113|pmid=27092007 |pmc=4983840 |bibcode=2016PNAS..113.5036S |doi-access=free }}</ref> End-Cretaceous trends in diversity may have varied between dinosaur lineages: it has been suggested that sauropods were not in decline, while ornithischians and theropods were in decline.<ref name="barrett2009">{{cite journal |last1=Barrett |first1=P.M. |last2=McGowan |first2=A.J. |last3=Page |first3=V. |year=2009 |title=Dinosaur diversity and the rock record |journal=Proceedings of the Royal Society B: Biological Sciences |volume=276 |issue=1667 |pages=2667–2674 |doi=10.1098/rspb.2009.0352|pmid=19403535 |pmc=2686664 }}</ref><ref name="upchurch2011">{{cite journal |last1=Upchurch |first1=P. |last2=Mannion |first2=P.D. |last3=Benson |first3=R.B. |last4=Butler |first4=R.J. |last5=Carrano |first5=M.T. |year=2011 |title=Geological and anthropogenic controls on the sampling of the terrestrial fossil record: a case study from the Dinosauria |journal=Geological Society, London, Special Publications |volume=358 |issue=1 |pages=209–240 |doi=10.1144/SP358.14|bibcode=2011GSLSP.358..209U |s2cid=130777837 }}</ref>

===Impact event===
{{Main|Chicxulub crater}}

[[File:LWA with Walt.JPG|thumb|upright|[[Luis Walter Alvarez|Luis]] (left) and his son [[Walter Alvarez]] (right) at the K-T Boundary in [[Gubbio]], Italy, 1981]]
[[File:Chicxulub radar topography.jpg|thumb|The [[Chicxulub Crater]] at the tip of the [[Yucatán Peninsula]]; the impactor that formed this crater may have caused the dinosaur [[extinction]].]]
The [[Alvarez hypothesis|bolide impact hypothesis]], first brought to wide attention in 1980 by [[Walter Alvarez]], [[Luis Walter Alvarez|Luis Alvarez]], and colleagues, attributes the K-Pg extinction event to a [[bolide]] (extraterrestrial projectile) impact.<ref>{{harvnb|Randall|2015}}</ref> Alvarez and colleagues proposed that a sudden increase in [[iridium]] levels, recorded around the world in rock deposits at the Cretaceous–Paleogene boundary, was direct evidence of the impact.<ref name="alvarez1980"/> [[Shocked quartz]], indicative of a strong shockwave emanating from an impact, was also found worldwide.<ref name="bohor1987">{{cite journal |last1=Bohor |first1=B.F. |last2=Modreski |first2=P.J. |last3=Foord |first3=E.E. |year=1987 |title=Shocked quartz in the Cretaceous-Tertiary boundary clays: Evidence for a global distribution |journal=Science |volume=236 |issue=4802 |pages=705–709 |doi=10.1126/science.236.4802.705 |pmid=17748309 |bibcode=1987Sci...236..705B |s2cid=31383614 |url=https://zenodo.org/record/1230978 |archive-date=February 26, 2021 |access-date=February 8, 2021 |archive-url=https://web.archive.org/web/20210226190627/https://zenodo.org/record/1230978 |url-status=live }}</ref> The actual impact site remained elusive until a [[Chicxulub crater|crater]] measuring {{convert|180|km|mi|abbr=on}} wide was discovered in the Yucatán Peninsula of southeastern [[Mexico]], and was publicized in a 1991 paper by [[Alan R. Hildebrand|Alan Hildebrand]] and colleagues.<ref name="hildebrand1991">{{cite journal |last1=Hildebrand |first1=A.R. |last2=Penfield |first2=G.T. |last3=Kring |first3=D.A. |last4=Pilkington |first4=M. |last5=Camargo |first5=Z.A. |last6=Jacobsen |first6=S.B. |last7=Boynton |first7=W.V. |year=1991 |title=Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico |journal=Geology |volume=19 |issue=9 |pages=867–871 |doi=10.1130/0091-7613(1991)019<0867:CCAPCT>2.3.CO;2|bibcode=1991Geo....19..867H }}</ref> Now, the bulk of the evidence suggests that a bolide {{convert|5|to|15|km|mi|frac=2|abbr=off|sp=us}} wide impacted the Yucatán Peninsula 66 million years ago, forming this crater<ref name="pope1996"/> and creating a "kill mechanism" that triggered the extinction event.<ref name="schulte2010">{{cite journal |last1=Schulte |first1=P. |last2=Alegret |first2=L. |last3=Arenillas |first3=I. |last4=Arz |first4=J.A. |last5=Barton |first5=P.J. |last6=Bown |first6=P.R. |last7=Bralower |first7=T.J. |last8=Christeson |first8=G.L. |last9=Claeys |first9=P. |last10=Cockell |first10=C.S. |last11=Collins |first11=G.S. |first12=A. |last12=Deutsch |first13=T.J. |last13=Goldin |first14=K. |last14=Goto |first15=J.M. |last15=Grajales-Nishimura |first16=R.A.F. |last16=Grieve |first17=S.P.S. |last17=Gulick  |first18=K.R. |last18=Johnson |first19=W. |last19=Kiessling |first20=C. |last20=Koeberl |first21=D.A. |last21=Kring |first22=K.G. |last22=MacLeod |first23=T. |last23=Matsui |first24=J. |last24=Melosh |first25=A. |last25=Montanari |first26=J.V. |last26=Morgan |first27=C.R. |last27=Neal |first28=D.J. |last28=Nichols |first29=R.D. |last29=Norris |first30=E. |last30=Pierazzo |first31=G. |last31=Ravizza |first32=M. |last32=Rebolledo-Vieyra |first33=W. |last33=Uwe Reimold |first34=E. |last34=Robin |first35=T. |last35=Salge |first36=R.P. |last36=Speijer |first37=A.R. |last37=Sweet |first38=J. |last38=Urrutia-Fucugauchi |first39=V. |last39=Vajda |first40=M.T. |last40=Whalen |first41=P.S. |last41=Willumsen |year=2010 |title=The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary |journal=Science |volume=327 |issue=5970 |pages=1214–1218 |doi=10.1126/science.1177265|pmid=20203042 |bibcode=2010Sci...327.1214S |s2cid=2659741 |url=https://lirias.kuleuven.be/handle/123456789/264213 }}</ref><ref name="kring2007">{{cite journal |last1=Kring |first1=D. A. |year=2007 |title=The Chicxulub impact event and its environmental consequences at the Cretaceous–Tertiary boundary |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=255 |issue=1–2 |pages=4–21 |doi=10.1016/j.palaeo.2007.02.037|bibcode=2007PPP...255....4K }}</ref><ref name="chiarenza2020">{{cite journal |last1=Chiarenza |first1=A.A. |last2=Farnsworth |first2=A. |last3=Mannion |first3=P.D. |last4=Lunt |first4=D.J. |last5=Valdes |first5=P.J. |last6=Morgan |first6=J.V.|author6-link= Joanna Morgan |last7=Allison |first7=P.A. |year=2020 |title=Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=29 |pages=17084–17093 |doi=10.1073/pnas.2006087117|pmid=32601204 |pmc=7382232 |bibcode=2020PNAS..11717084C |doi-access=free }}</ref>

Within hours, the Chicxulub impact would have created immediate effects such as earthquakes,<ref name="ivanov2005">{{cite journal |last1=Ivanov |first1=B.A. |year=2005 |title=Numerical Modeling of the Largest Terrestrial Meteorite Craters |journal=Solar System Research |volume=39 |issue=5 |pages=381–409 |doi=10.1007/s11208-005-0051-0|bibcode=2005SoSyR..39..381I |s2cid=120305483 }}</ref> tsunamis,<ref name="matsui2002">{{cite journal |last1=Matsui |first1=T. |last2=Imamura |first2=F. |last3=Tajika |first3=E. |last4=Nakano |first4=Y. |last5=Fujisawa |first5=Y. |year=2002 |title=Generation and propagation of a tsunami from the Cretaceous-Tertiary impact event |journal=Geological Society of America Special Papers |volume=356 |pages=69–78 |doi=10.1130/0-8137-2356-6.69|isbn=978-0-8137-2356-3 }}</ref> and a global firestorm that likely killed unsheltered animals and started wildfires.<ref name="robertson2004">{{cite journal |last1=Robertson |first1=D.S. |last2=McKenna |first2=M.C. |author2-link=Malcolm McKenna |last3=Toon |first3=O.B. |author3-link=Owen Toon |last4=Hope |first4=S. |last5=Lillegraven |first5=J.A. |display-authors=3 |year=2004 |title=Survival in the first hours of the Cenozoic |url=http://webh01.ua.ac.be/funmorph/raoul/macroevolutie/Robertson2004.pdf |journal=[[Geological Society of America Bulletin]] |volume=116 |issue=5–6 |pages=760–768 |bibcode=2004GSAB..116..760R |doi=10.1130/B25402.1 |issn=0016-7606 |archive-url=https://web.archive.org/web/20120918141759/http://webh01.ua.ac.be/funmorph/raoul/macroevolutie/Robertson2004.pdf |archive-date=September 18, 2012 |access-date=June 15, 2011}}</ref><ref name="robertson2013">{{cite journal |last1=Robertson |first1=D.S. |last2=Lewis |first2=W.M. |last3=Sheehan |first3=P.M. |last4=Toon |first4=O.B. |year=2013 |title=K-Pg extinction: Reevaluation of the heat-fire hypothesis |journal=Journal of Geophysical Research: Biogeosciences |volume=118 |issue=1 |pages=329–336 |doi=10.1002/jgrg.20018|bibcode=2013JGRG..118..329R |s2cid=17015462 |doi-access=free }}</ref> However, it would also have had longer-term consequences for the environment. Within days, sulfate [[aerosol]]s released from rocks at the impact site would have contributed to [[acid rain]] and [[ocean acidification]].<ref name="pope1997">{{cite journal |last1=Pope |first1=K.O. |last2=Baines |first2=K.H. |last3=Ocampo |first3=A.C. |last4=Ivanov |first4=B.A. |year=1997 |title=Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact |journal=Journal of Geophysical Research: Planets |volume=102 |issue=E9 |pages=21645–21664 |doi=10.1029/97JE01743|pmid=11541145 |bibcode=1997JGR...10221645P |s2cid=8447773 |doi-access=free }}</ref><ref name="ohno2014"/> [[Soot]] aerosols are thought to have spread around the world over the ensuing months and years; they would have cooled the surface of the Earth by reflecting [[thermal radiation]], and greatly slowed [[photosynthesis]] by blocking out sunlight, thus creating an [[impact winter]].<ref name="brusatte2014"/><ref name="kaiho2016">{{cite journal |last1=Kaiho |first1=K. |last2=Oshima |first2=N. |last3=Adachi |first3=K. |last4=Adachi |first4=Y. |last5=Mizukami |first5=T. |last6=Fujibayashi |first6=M. |last7=Saito |first7=R. |year=2016 |title=Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction |journal=Scientific Reports |volume=6 |issue=1 |pages=1–13 |doi=10.1038/srep28427|pmid=27414998 |pmc=4944614 |bibcode=2016NatSR...628427K }}</ref><ref name="lyons2020">{{cite journal |last1=Lyons |first1=S.L. |last2=Karp |first2=A.T. |last3=Bralower |first3=T.J. |last4=Grice |first4=K. |last5=Schaefer |first5=B. |last6=Gulick |first6=S.P. |last7=Morgan |first7=J.V.|author7-link= Joanna Morgan |last8=Freeman |first8=K.H. |year=2020 |title=Organic matter from the Chicxulub crater exacerbated the K–Pg impact winter |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=41 |pages=25327–25334 |doi=10.1073/pnas.2004596117|pmid=32989138 |pmc=7568312 |bibcode=2020PNAS..11725327L |doi-access=free }}</ref> (This role was ascribed to [[sulfate]] aerosols until experiments demonstrated otherwise.<ref name="ohno2014">{{cite journal |last1=Ohno |first1=S. |last2=Kadono |first2=T. |last3=Kurosawa |first3=K. |last4=Hamura |first4=T. |last5=Sakaiya |first5=T. |last6=Shigemori |first6=K. |last7=Hironaka |first7=Y. |last8=Sano |first8=T. |last9=Watari |first9=T. |last10=Otani |first10=K. |last11=Matsui |first11=T. |last12=Sugita |first12=S. |year=2014 |title=Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification |journal=Nature Geoscience |volume=7 |issue=4 |pages=279–282 |doi=10.1038/ngeo2095|bibcode=2014NatGe...7..279O }}</ref>) The cessation of photosynthesis would have led to the collapse of [[food web]]s depending on leafy plants, which included all dinosaurs save for grain-eating birds.<ref name="larson2016"/>

===Deccan Traps===
{{Main|Deccan Traps}}
 <!-- This section is linked from [[Cretaceous–Paleogene extinction event]] -->

At the time of the K-Pg extinction, the [[Deccan Traps]] flood basalts of India were actively erupting. The eruptions can be separated into three phases around the K-Pg boundary, two prior to the boundary and one after. The second phase, which occurred very close to the boundary, would have extruded 70 to 80% of the volume of these eruptions in intermittent pulses that occurred around 100,000 years apart.<ref name="chenet2009">{{cite journal |last1=Chenet |first1=A.L. |last2=Courtillot |first2=V. |last3=Fluteau |first3=F. |last4=Gérard |first4=M. |last5=Quidelleur |first5=X. |last6=Khadri |first6=S.F.R. |last7=Subbarao |first7=K.V. |last8=Thordarson |first8=T. |year=2009 |title=Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500-m-thick composite section |journal=Journal of Geophysical Research: Solid Earth |volume=114 |issue=B6 |pages=B06103 |doi=10.1029/2008JB005644|bibcode=2009JGRB..114.6103C |s2cid=140541003 |url=https://hal.archives-ouvertes.fr/hal-00406544/file/2008JB005644.pdf }}</ref><ref name="schoene2019">{{cite journal |last1=Schoene |first1=B. |last2=Eddy |first2=M.P. |last3=Samperton |first3=K.M. |last4=Keller |first4=C.B. |last5=Keller |first5=G. |last6=Adatte |first6=T. |last7=Khadri |first7=S.F. |year=2019 |title=U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction |journal=Science |volume=363 |issue=6429 |pages=862–866 |doi=10.1126/science.aau2422|pmid=30792300 |bibcode=2019Sci...363..862S |osti=1497969 |s2cid=67876950 |doi-access=free }}</ref> [[Greenhouse gases]] such as [[carbon dioxide]] and [[sulfur dioxide]] would have been released by this volcanic activity,<ref name="mclean1985">{{cite journal |last1=McLean |first1=D.M. |year=1985 |title=Deccan Traps mantle degassing in the terminal Cretaceous marine extinctions |journal=Cretaceous Research |volume=6 |issue=3 |pages=235–259 |doi=10.1016/0195-6671(85)90048-5|bibcode=1985CrRes...6..235M }}</ref><ref name="self2006">{{cite journal |last1=Self |first1=S. |last2=Widdowson |first2=M. |last3=Thordarson |first3=T. |last4=Jay |first4=A.E. |year=2006 |title=Volatile fluxes during flood basalt eruptions and potential effects on the global environment: A Deccan perspective |journal=Earth and Planetary Science Letters |volume=248 |issue=1–2 |pages=518–532 |doi=10.1016/j.epsl.2006.05.041|bibcode=2006E&PSL.248..518S }}</ref> resulting in [[climate change]] through temperature perturbations of roughly {{convert|3|C-change}} but possibly as high as {{convert|7|C-change}}.<ref name="tobin2017">{{cite journal |last1=Tobin |first1=T.S. |last2=Bitz |first2=C.M. |last3=Archer |first3=D. |year=2017 |title=Modeling climatic effects of carbon dioxide emissions from Deccan Traps volcanic eruptions around the Cretaceous–Paleogene boundary |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=478 |pages=139–148 |doi=10.1016/j.palaeo.2016.05.028|bibcode=2017PPP...478..139T }}</ref> Like the Chicxulub impact, the eruptions may also have released sulfate aerosols, which would have caused acid rain and global cooling.<ref name="schmidt2016">{{cite journal |last1=Schmidt |first1=A. |last2=Skeffington |first2=R.A. |last3=Thordarson |first3=T. |last4=Self |first4=S. |last5=Forster |first5=P.M. |last6=Rap |first6=A. |last7=Ridgwell |first7=A. |last8=Fowler |first8=D. |last9=Wilson |first9=M. |last10=Mann |first10=G.W. |last11=Wignall |first11=P.B. |last12=Carslaw |first12=K.S. |year=2016 |title=Selective environmental stress from sulphur emitted by continental flood basalt eruptions |journal=Nature Geoscience |volume=9 |issue=1 |pages=77–82 |doi=10.1038/ngeo2588|bibcode=2016NatGe...9...77S |s2cid=59518452 |url=http://eprints.whiterose.ac.uk/92239/1/Schmidt_et_al_NGS_accepted.pdf |archive-url=https://web.archive.org/web/20170922012438/http://eprints.whiterose.ac.uk/92239/1/Schmidt_et_al_NGS_accepted.pdf |archive-date=2017-09-22 |url-status=live }}</ref> However, due to large error margins in the dating of the eruptions, the role of the Deccan Traps in the K-Pg extinction remains unclear.<ref name="renne2013"/><ref name="brusatte2014"/><ref name="hofman2000"/>

Before 2000, arguments that the Deccan Traps eruptions—as opposed to the Chicxulub impact—caused the extinction were usually linked to the view that the extinction was gradual. Prior to the discovery of the Chicxulub crater, the Deccan Traps were used to explain the global iridium layer;<ref name="mclean1985"/><ref name="sahni1988">{{cite journal |last1=Sahni |first1=A. |year=1988 |title=Cretaceous-Tertiary boundary events: Mass extinctions, iridium enrichment and Deccan volcanism |journal=Current Science |volume=57 |issue=10 |pages=513–519 |jstor=24090754}}</ref> even after the crater's discovery, the impact was still thought to only have had a regional, not global, effect on the extinction event.<ref name="glasby1996">{{cite journal |last1=Glasby |first1=G.P. |last2=Kunzendorf |first2=H. |year=1996 |title=Multiple factors in the origin of the Cretaceous/Tertiary boundary: the role of environmental stress and Deccan Trap volcanism |journal=Geologische Rundschau |volume=85 |issue=2 |pages=191–210 |doi=10.1007/BF02422228|pmid=11543126 |bibcode=1996IJEaS..85..191G |s2cid=19155384 }}</ref> In response, Luis Alvarez rejected volcanic activity as an explanation for the iridium layer and the extinction as a whole.<ref name="alvarez1987">{{cite report |last1=Alvarez |first1=L.W. |year=1987 |title=Mass Extinctions Caused by Large Bolide Impacts |url=https://www.osti.gov/servlets/purl/875729 |docket=LBL-22786 |page=39 |publisher=[[Lawrence Berkeley National Laboratory|Lawrence Berkeley Laboratory]] |access-date=January 27, 2021}}</ref> Since then, however, most researchers have adopted a more moderate position, which identifies the Chicxulub impact as the primary progenitor of the extinction while also recognizing that the Deccan Traps may also have played a role. Walter Alvarez himself has acknowledged that the Deccan Traps and other ecological factors may have contributed to the extinctions in addition to the Chicxulub impact.<ref name="alvarez1997"/> Some estimates have placed the start of the second phase in the Deccan Traps eruptions within 50,000 years after the Chicxulub impact.<ref name="renne2015">{{cite journal |last1=Renne |first1=P.R. |last2=Sprain |first2=C.J. |last3=Richards |first3=M.A. |last4=Self |first4=S. |last5=Vanderkluysen |first5=L. |last6=Pande |first6=K. |year=2015 |title=State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact |journal=Science |volume=350 |issue=6256 |pages=76–78 |doi=10.1126/science.aac7549 |pmid=26430116 |bibcode=2015Sci...350...76R |s2cid=30612906 |url=https://escholarship.org/uc/item/5fk799n8 |doi-access=free |archive-date=March 23, 2023 |access-date=October 28, 2022 |archive-url=https://web.archive.org/web/20230323005826/https://escholarship.org/uc/item/5fk799n8 |url-status=live }}</ref> Combined with mathematical modelling of the [[seismic wave]]s that would have been generated by the impact, this has led to the suggestion that the Chicxulub impact may have triggered these eruptions by increasing the permeability of the [[mantle plume]] underlying the Deccan Traps.<ref name="richards2015">{{cite journal |last1=Richards |first1=M.A. |last2=Alvarez |first2=W. |last3=Self |first3=S. |last4=Karlstrom |first4=L. |last5=Renne |first5=P.R. |last6=Manga |first6=M. |last7=Sprain |first7=C.J. |last8=Smit |first8=J. |last9=Vanderkluysen |first9=L. |last10=Gibson |first10=S.A. |year=2015 |title=Triggering of the largest Deccan eruptions by the Chicxulub impact |journal=Geological Society of America Bulletin |volume=127 |issue=11–12 |pages=1507–1520 |doi=10.1130/B31167.1 |bibcode=2015GSAB..127.1507R |osti=1512141 |s2cid=3463018 |url=https://escholarship.org/uc/item/86f3521g |archive-date=October 22, 2020 |access-date=February 8, 2021 |archive-url=https://web.archive.org/web/20201022102243/https://escholarship.org/uc/item/86f3521g |url-status=live |hdl=1871.1/cc9361fe-f586-44a0-90ac-f5c513e9920b |hdl-access=free }}</ref><ref name="khazins2019">{{cite book |last1=Khazins |first1=V. |last2=Shuvalov |first2=V. |year=2019 |editor-first1=G. |editor-last1=Kocharyan |editor-first2=A. |editor-last2=Lyakhov |chapter=Chicxulub Impact as a Trigger of One of Deccan Volcanism Phases: Threshold of Seismic Energy Density |title=Trigger Effects in Geosystems |pages=523–530 |publisher=Springer |location=Cham |series=Springer Proceedings in Earth and Environmental Sciences |doi=10.1007/978-3-030-31970-0_55|isbn=978-3-030-31969-4 |s2cid=210277965 }}</ref>

Whether the Deccan Traps were a major cause of the extinction, on par with the Chicxulub impact, remains uncertain. Proponents consider the climatic impact of the sulfur dioxide released to have been on par with the Chicxulub impact, and also note the role of flood basalt volcanism in other mass extinctions like the [[Permian-Triassic extinction event]].<ref name="archibald2010">{{cite journal |first1=J.D. |last1=Archibald |first2=W.A. |last2=Clemens |first3=K. |last3=Padian |first4=T. |last4=Rowe |first5=N. |last5=Macleod |first6=P.M. |last6=Barrett |first7=A. |last7=Gale |first8=P. |last8=Holroyd |first9=H.-D. |last9=Sues |first10=N.C. |last10=Arens |first11=J.R. |last11=Horner |first12=G.P. |last12=Wilson |first13=M.B. |last13=Goodwin |first14=C.A. |last14=Brochu |first15=D.L. |last15=Lofgren |first16=S.H. |last16=Hurlbert |first17=J.H. |last17=Hartman |first18=D.A. |last18=Eberth |first19=P.B. |last19=Wignall |first20=P.J. |last20=Currie |first21=A. |last21=Weil |first22=G.V.R. |last22=Prasad |first23=L. |last23=Dingus |first24=V. |last24=Courtillot |first25=A. |last25=Milner |first26=A. |last26=Milner |first27=S. |last27=Bajpai |first28=D.J. |last28=Ward |first29=A. |last29=Sahni |year=2010 |title=Cretaceous extinctions: multiple causes |journal=Science |volume=328 |issue=5981 |pages=973; author reply 975–6 |doi=10.1126/science.328.5981.973-a|pmid=20489004 }}</ref><ref name="courtillot2010">{{cite journal |last1=Courtillot |first1=V. |last2=Fluteau |first2=F. |year=2010 |title=Cretaceous extinctions: the volcanic hypothesis |journal=Science |volume=328 |issue=5981 |pages=973–974 |doi=10.1126/science.328.5981.973-b|pmid=20489003 |bibcode=2010Sci...328..973C }}</ref> They consider the Chicxulub impact to have worsened the ongoing climate change caused by the eruptions.<ref name="keller2014">{{cite journal |last1=Keller |first1=G. |year=2014 |title=Deccan volcanism, the Chicxulub impact, and the end-Cretaceous mass extinction: Coincidence? Cause and effect |journal=Geological Society of America Special Papers |volume=505 |pages=57–89 |doi=10.1130/2014.2505(03)|isbn=978-0-8137-2505-5 }}</ref> Meanwhile, detractors point out the sudden nature of the extinction and that other pulses in Deccan Traps activity of comparable magnitude did not appear to have caused extinctions. They also contend that the causes of different mass extinctions should be assessed separately.<ref name="schulte2010reply">{{cite journal |last1=Schulte |first1=P. |last2=Alegret |first2=L. |last3=Arenillas |first3=I. |last4=Arz |first4=J.A. |last5=Barton |first5=P.J. |last6=Bown |first6=P.R. |last7=Bralower |first7=T.J. |last8=Christeson |first8=G.L. |last9=Claeys |first9=P. |last10=Cockell |first10=C.S. |last11=Collins |first11=G.S. |first12=A. |last12=Deutsch |first13=T.J. |last13=Goldin |first14=K. |last14=Goto |first15=J.M. |last15=Grajales-Nishimura |first16=R.A.F. |last16=Grieve |first17=S.P.S. |last17=Gulick  |first18=K.R. |last18=Johnson |first19=W. |last19=Kiessling |first20=C. |last20=Koeberl |first21=D.A. |last21=Kring |first22=K.G. |last22=MacLeod |first23=T. |last23=Matsui |first24=J. |last24=Melosh |first25=A. |last25=Montanari |first26=J.V. |last26=Morgan|author26-link= Joanna Morgan |first27=C.R. |last27=Neal |first28=D.J. |last28=Nichols |first29=R.D. |last29=Norris |first30=E. |last30=Pierazzo |first31=G. |last31=Ravizza |first32=M. |last32=Rebolledo-Vieyra |first33=W. |last33=Uwe Reimold |first34=E. |last34=Robin |first35=T. |last35=Salge |first36=R.P. |last36=Speijer |first37=A.R. |last37=Sweet |first38=J. |last38=Urrutia-Fucugauchi |first39=V. |last39=Vajda |first40=M.T. |last40=Whalen |first41=P.S. |last41=Willumsen |year=2010 |title=Response—Cretaceous extinctions |journal=Science |volume=328 |issue=5981 |pages=975–976 |doi=10.1126/science.328.5981.975|bibcode=2010Sci...328..975S |url=https://lirias.kuleuven.be/handle/123456789/269158 }}</ref> In 2020, Alfio Chiarenza and colleagues suggested that the Deccan Traps may even have had the opposite effect: they suggested that the long-term warming caused by its carbon dioxide emissions may have dampened the impact winter from the Chicxulub impact.<ref name="chiarenza2020"/>

===Possible Paleocene survivors===
Non-avian dinosaur remains have occasionally been found above the K-Pg boundary. In 2000, [[Spencer G. Lucas|Spencer Lucas]] and colleagues reported the discovery of a single hadrosaur right femur in the [[San Juan Basin]] of [[New Mexico]], and described it as evidence of Paleocene dinosaurs. The rock unit in which the bone was discovered has been dated to the early [[Paleocene]] epoch, approximately 64.8 million years ago.<ref name="fassett2011"/> If the bone was not [[deposition (geology)|re-deposited]] by weathering action, it would provide evidence that some dinosaur populations survived at least half a million years into the Cenozoic.<ref name="fassett2009"/> Other evidence includes the presence of dinosaur remains in the Hell Creek Formation up to {{convert|1.3|m|ft|abbr=on}} above the Cretaceous–Paleogene boundary, representing 40,000 years of elapsed time. This has been used to support the view that the K-Pg extinction was gradual.<ref name="sloan1986"/> However, these supposed Paleocene dinosaurs are considered by many other researchers to be [[reworked fossil|reworked]], that is, washed out of their original locations and then reburied in younger sediments.<ref name="lucas2009">{{cite journal |last1=Lucas |first1=S.G. |last2=Sullivan |first2=R.M. |last3=Cather |first3=S.M. |last4=Jasinski |first4=S.E. |last5=Fowler |first5=D.W. |last6=Heckert |first6=A.B. |last7=Spielmann |first7=J.A. |last8=Hunt |first8=A.P. |year=2009 |title=No definitive evidence of Paleocene dinosaurs in the San Juan Basin |journal=Palaeontologia Electronica |volume=12 |issue=2 |page=8A}}</ref><ref name="renne2012">{{cite journal |last1=Renne |first1=P.R. |last2=Goodwin |first2=M.B. |year=2012 |title=Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: COMMENT |journal=Geology |volume=40 |issue=4 |pages=e259 |doi=10.1130/G32521C.1|bibcode=2012Geo....40E.259R |doi-access=free }}</ref><ref name="lofgren1990">{{cite journal |last1=Lofgren |first1=D.L. |last2=Hotton |first2=C.L. |last3=Runkel |first3=A.C. |year=1990 |title=Reworking of Cretaceous dinosaurs into Paleocene channel, deposits, upper Hell Creek Formation, Montana |journal=Geology |volume=18 |issue=9 |pages=874–877 |doi=10.1130/0091-7613(1990)018<0874:ROCDIP>2.3.CO;2|bibcode=1990Geo....18..874L }}</ref> The age estimates have also been considered unreliable.<ref name="koenig2012">{{cite journal |last1=Koenig |first1=A.E. |last2=Lucas |first2=S.G. |last3=Neymark |first3=L.A. |last4=Heckert |first4=A.B. |last5=Sullivan |first5=R.M. |last6=Jasinski |first6=S.E. |last7=Fowler |first7=D.W. |year=2012 |title=Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: COMMENT |journal=Geology |volume=40 |issue=4 |pages=e262 |doi=10.1130/G32154C.1|bibcode=2012Geo....40E.262K |doi-access=free }}</ref>

==Cultural depictions==
{{Main|Cultural depictions of dinosaurs}}
[[File:Iguanodon Crystal Palace.jpg|thumb|Outdated ''[[Iguanodon]]'' statues created by [[Benjamin Waterhouse Hawkins]] for the [[Crystal Palace Park]] in 1853]]
[[File:Winsor McCay (1914)Gertie the Dinosaur.webm|thumb|right|alt=Animated film of a trained dinosaur.|thumbtime=16:46|''[[Gertie the Dinosaur]]'' (1914) by [[Winsor McCay]], featuring the first animated dinosaur]]

By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the popular imagination and become an enduring part of human culture. The entry of the word "dinosaur" into the common [[vernacular]] reflects the animals' cultural importance: in English, "dinosaur" is commonly used to describe anything that is impractically large, obsolete, or bound for extinction.<ref name="m-w"/>

Public enthusiasm for dinosaurs first developed in [[Victorian era|Victorian]] England, where in 1854, three decades after the first scientific descriptions of dinosaur remains, a menagerie of lifelike [[Crystal Palace dinosaurs|dinosaur sculptures]] was unveiled in [[London]]'s [[Crystal Palace Park]]. The Crystal Palace dinosaurs proved so popular that a strong market in smaller replicas soon developed. In subsequent decades, dinosaur exhibits opened at parks and [[Natural history museum|museums]] around the world, ensuring that successive generations would be introduced to the animals in an immersive and exciting way.<ref name=torrens1993/> The enduring popularity of dinosaurs, in its turn, has resulted in significant public funding for dinosaur science, and has frequently spurred new discoveries. In the United States, for example, the competition between museums for public attention led directly to the Bone Wars of the 1880s and 1890s, during which a pair of feuding paleontologists made enormous scientific contributions.<ref name=breithaupt1997/>

The popular preoccupation with dinosaurs has ensured their appearance in [[literature]], [[film]], and other [[Media (communication)|media]]. Beginning in 1852 with a passing mention in [[Charles Dickens]]{{'}} ''[[Bleak House]]'',<ref name=bleakhouse/> dinosaurs have been featured in large numbers of [[fiction]]al works. [[Jules Verne]]'s 1864 novel ''[[Journey to the Center of the Earth]]'', [[Arthur Conan Doyle|Sir Arthur Conan Doyle]]'s 1912 book ''[[The Lost World (Doyle novel)|The Lost World]]'', the 1914 animated film ''[[Gertie the Dinosaur]]'' (featuring the first animated dinosaur), the iconic 1933 [[motion picture|film]] ''[[King Kong (1933 film)|King Kong]]'', the 1954 ''[[Godzilla (1954 film)|Godzilla]]'' and its many sequels, the best-selling 1990 novel ''[[Jurassic Park (novel)|Jurassic Park]]'' by [[Michael Crichton]] and its 1993 [[Jurassic Park (film)|film adaptation]] are just a few notable examples of dinosaur appearances in fiction. Authors of general-interest [[non-fiction]] works about dinosaurs, including some prominent paleontologists, have often sought to use the animals as a way to educate readers about science in general. Dinosaurs are ubiquitous in [[advertising]]; numerous [[Company (law)|companies]] have referenced dinosaurs in printed or televised advertisements, either in order to sell their own products or in order to characterize their rivals as slow-moving, dim-witted, or obsolete.<ref name=DFGlut1997/><ref>{{cite book |last1=Lee |first1=Newton |last2=Madej |first2=Krystina |title=Disney Stories |chapter=Early Animation: Gags and Situations |date=2012 |pages=17–24 |doi=10.1007/978-1-4614-2101-6_3|isbn=978-1-4614-2100-9 |s2cid=192335675 }}</ref>

==See also==
{{Portal|left=yes|Dinosaurs|Paleontology}}
* [[Dinosaur diet and feeding]]
* [[Evolutionary history of life]]
* [[Lists of dinosaur-bearing stratigraphic units]]
* [[List of dinosaur genera]]
* [[List of bird genera]]
* [[List of birds]]
* [[List of informally named dinosaurs]]
* [[List of films featuring dinosaurs]]

==Notes==
{{Reflist|group=note}}

==References==
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<ref name=Holland1909>This was recognized not later than 1909: {{cite web |url=http://www.hmnh.org/library/diplodocus/holland1910.html |title=Dr. W. J. Holland and the Sprawling Sauropods |last=Celeskey |first=Matt |year=2005 |website=The Hairy Museum of Natural History |archive-url=https://web.archive.org/web/20110612180650/http://www.hmnh.org/library/diplodocus/holland1910.html |archive-date=June 12, 2011 |access-date=October 18, 2019}}
* {{cite journal |last=Holland |first=William J. |author-link=William Jacob Holland |date=May 1910 |title=A Review of Some Recent Criticisms of the Restorations of Sauropod Dinosaurs Existing in the Museums of the United States, with Special Reference to that of ''Diplodocus Carnegiei'' in the Carnegie Museum |url=https://archive.org/details/jstor-2455581 |journal=[[The American Naturalist]] |publisher=[[American Society of Naturalists]] |volume=44 |issue=521 |pages=259–283 |issn=0003-0147 |access-date=October 18, 2019|doi=10.1086/279138 |bibcode=1910ANat...44..258H |s2cid=84424110 }}
* The arguments and many of the images are also presented in {{harvnb|Desmond|1975}}.</ref>
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<ref name=LSJ>{{cite web |url=https://www.perseus.tufts.edu/hopper/resolveform?type=start&lookup=deino%2Fs&lang=greek |title=Greek Dictionary Headword Search Results |editor-last=Crane |editor-first=George R. |website=[[Perseus Project|Perseus 4.0]] |publisher=[[Tufts University]] |location=[[Medford, Massachusetts|Medford]] and [[Somerville, Massachusetts|Somerville, MA]] |access-date=October 13, 2019 |archive-date=December 10, 2019 |archive-url=https://web.archive.org/web/20191210013213/https://www.perseus.tufts.edu/hopper/resolveform?type=start&lookup=deino%2Fs&lang=greek |url-status=live }} Lemma for '[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Ddeino%2Fs1 δεινός] {{Webarchive|url=https://web.archive.org/web/20191210013242/https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Ddeino%2Fs1 |date=December 10, 2019 }}' from [[Henry Liddell|Henry George Liddell]], [[Robert Scott (philologist)|Robert Scott]], ''[[A Greek–English Lexicon|A Greek-English Lexicon]]'' (1940): 'fearful, terrible'.</ref>
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* {{cite book |last=Owen |first=Richard |author-link=Richard Owen |chapter=Report on British Fossil Reptiles. Part II |chapter-url=https://archive.org/details/reportofeleventh42lond/page/n99 |date=1842 |title=Report of the Eleventh Meeting of the British Association for the Advancement of Science; Held at Plymouth in July 1841 |url=https://archive.org/details/reportofeleventh42lond/page/n3/mode/2up |location=[[London]] |publisher=[[John Murray (publishing house)|John Murray]] |pages=[https://archive.org/details/reportofeleventh42lond/page/60 60]–204 |lccn=99030427 |oclc=1015526268 |access-date=October 13, 2019 }}
* {{cite book |editor-last=Padian |editor-first=Kevin |year=1986 |title=The Origin of Birds and the Evolution of Flight |series=Memoirs of the California Academy of Sciences |volume=8 |location=San Francisco, CA |publisher=[[California Academy of Sciences]] |isbn=978-0-940228-14-6 |oclc=946083441 |ol=9826926M}}
* {{cite book |last=Parsons |first=Keith M. |year=2001 |title=Drawing out Leviathan: Dinosaurs and the Science Wars |url=https://archive.org/details/drawingoutleviat0000pars |url-access=registration |series=Life in the Past |location=Bloomington, IN |publisher=Indiana University Press |isbn=978-0-253-33937-9 |lccn=2001016803 |oclc=50174737 |access-date=October 30, 2019 }}
* {{cite book |last=Paul |first=Gregory S. |author-link=Gregory S. Paul |year=1988 |title=Predatory Dinosaurs of the World: A Complete Illustrated Guide |url=https://archive.org/details/predatorydinosaursoftheworld1988 |location=New York |publisher=[[Simon & Schuster]] |isbn=978-0-671-61946-6 |lccn=88023052 |oclc=859819093 |access-date=October 30, 2019 }}
* {{cite book |editor-last=Paul |editor-first=Gregory S. |year=2000 |title=The Scientific American Book of Dinosaurs |edition=1st |location=New York |publisher=[[St. Martin's Press]] |isbn=978-0-312-26226-6|lccn=2001269051 |oclc=45256074}}
* {{cite book |last=Paul |first=Gregory S. |year=2010 |title=The Princeton Field Guide to Dinosaurs |series=Princeton Field Guides |location=Princeton, NJ |publisher=Princeton University Press |isbn=978-0-691-13720-9|lccn=2010014916 |oclc=907619291|title-link=The Princeton Field Guide to Dinosaurs}}
* {{cite book |last=Plot |first=Robert |author-link=Robert Plot |year=1677 |title=The Natural History of Oxford-shire: Being an Essay toward the Natural History of England |url=https://archive.org/details/naturalhistoryo00plot/page/n9 |location=Oxford; London |publisher=S. Millers |lccn=11004267 |oclc=933062622 |access-date=November 13, 2019}}
* {{cite book |last=Randall |first=Lisa |author-link=Lisa Randall |year=2015 |title=Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe |location=New York |publisher=[[HarperCollins]] |isbn=978-0-06-232847-2 |lccn=2016427646 |oclc=962371431|title-link=Dark Matter and the Dinosaurs}}
* {{cite book |last=Rupke |first=Nicolaas A. |author-link=Nicolaas Adrianus Rupke |year=1994 |title=Richard Owen: Victorian Naturalist |url=https://archive.org/details/richardowenvicto00rupk |url-access=registration|location=New Haven |publisher=[[Yale University Press]] |isbn=978-0-300-05820-8 |lccn=93005739 |oclc=844183804 |access-date=November 5, 2019}}
* {{cite book |editor-last=Sarjeant |editor-first=William A.S. |editor-link=William Sarjeant |year=1995 |title=Vertebrate Fossils and the Evolution of Scientific Concepts: Writings in Tribute to Beverly Halstead, by Some of His Many Friends |series=Modern Geology, vol. 18 |location=Amsterdam |publisher=Gordon and Breach Publishers |isbn=978-2-88124-996-9 |lccn=00500382 |oclc=34672546 |issn=0026-7775}} "Reprint of papers published in a special volume of Modern geology [v. 18 (Halstead memorial volume), 1993], with five additional contributions.--Pref."
* {{cite journal |editor1-last=Tanner |editor1-first=Lawrence H. |editor2-last=Spielmann |editor2-first=Justin A. |editor3-last=Lucas |editor3-first=Spencer G. |year=2013 |title=The Triassic System: New Developments in Stratigraphy and Paleontology |journal=Bulletin of the New Mexico Museum of Natural History and Science |url=https://econtent.unm.edu/digital/collection/bulletins/id/1645/rec/1 |series=New Mexico Museum of Natural History and Science Bulletin |volume=61|location=Albuquerque, NM |publisher=New Mexico Museum of Natural History and Science |issn=1524-4156 |oclc=852432407 |access-date=October 21, 2019}}
* {{cite book |editor1-last=Weishampel |editor1-first=David B. |editor1-link=David B. Weishampel |editor2-last=Dodson |editor2-first=Peter |editor3-last=Osmólska |editor3-first=Halszka |editor3-link=Halszka Osmólska|year=2004 |title=The Dinosauria |edition=2nd |location=Berkeley |publisher=University of California Press |isbn=978-0-520-25408-4 |lccn=2004049804 |oclc=154697781|title-link=The Dinosauria}}
{{Refend}}

==Further reading==
{{Library resources box
 |onlinebooks=yes
 |by=no
 |lcheading= Dinosaurs
 |label=Dinosaurs
 }}
* {{cite book |last=Paul |first=Gregory S. |year=2002 |title=Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds |location=[[Baltimore]]; London |publisher=[[Johns Hopkins University Press]]|isbn=978-0-8018-6763-7 |lccn=2001000242 |oclc=1088130487 |url-access=registration |url=https://archive.org/details/dinosaursofairev0000paul}}.
* {{cite book |last=Sternberg |first=Charles Mortram |author-link=Charles Mortram Sternberg |year=1966 |orig-date=Original edition published by E. Cloutier, printer to the King, 1946 |title=Canadian Dinosaurs|series=Geological Series |volume=54|edition=2nd |location=[[Ottawa]] |publisher=[[National museums of Canada|National Museum of Canada]] |lccn=gs46000214 |oclc=1032865683}}
* {{cite book |author=Stewart, Tabori & Chang |year=1997 |title=The Humongous Book of Dinosaurs |location=New York |publisher=[[Abrams Books|Stewart, Tabori & Chang]] |isbn=978-1-55670-596-0 |lccn=97000398|oclc=1037269801 |title-link=The Humongous Book of Dinosaurs}} 
* {{cite web |author=University of Southampton |title=Two New Species of Large Predatory Dinosaur with Crocodile-Like Skulls Discovered on Isle of Wight |website=SciTechDaily |date=September 29, 2021 |url=https://scitechdaily.com/two-new-species-of-large-predatory-dinosaur-with-crocodile-like-skulls-discovered-on-isle-of-wight/}}
* {{cite journal|last1=Zhou |first1=Zhonghe |date=October 2004 |title=The origin and early evolution of birds: discoveries, disputes, and perspectives from fossil evidence |url=http://www.cisneros-heredia.org/infotrans/usfq/ornitofauna/pdfs/zhou2004.pdf |journal=Naturwissenschaften |location=Berlin |publisher=Springer Science+Business Media |volume=91|issue=10 |pages=455–471 |bibcode=2004NW.....91..455Z |doi=10.1007/s00114-004-0570-4|issn=0028-1042 |pmid=15365634 |s2cid=3329625 |archive-url=https://web.archive.org/web/20110721144552/http://www.cisneros-heredia.org/infotrans/usfq/ornitofauna/pdfs/zhou2004.pdf |archive-date=July 21, 2011 |access-date=November 6, 2019}}

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