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{{Taxobox
| name = Dinosaurs
| fossil_range = {{fossil range|230.0|65.5}}[[Triassic]] – [[Cretaceous]]<br /> <small>(excluding [[Aves]])</small>
| image = field_dinos_2.jpg
| image_width = 260px
| image_caption = Mounted skeletons of ''[[Tyrannosaurus]]'' (left) and ''[[Apatosaurus]]'' (right) at the [[American Museum of Natural History]].
| regnum = [[Animal]]ia
| phylum = [[Chordate|Chordata]]
|subphylum = [[Vertebrate|Vertebrata]]
| classis = [[Reptile|Sauropsida]]
| subclassis = [[Diapsid]]a
| infraclassis = [[Archosauromorpha]]
| superordo = '''Dinosauria'''
| superordo_authority = [[Richard Owen|Owen]], 1842
| subdivision_ranks = [[Order (biology)|Orders]] and [[Order (biology)|suborders]]
| subdivision = <div>
* '''[[Ornithischia]]'''
** [[Cerapoda]]
** [[Thyreophora]]
* '''[[Saurischia]]'''
** [[Sauropodomorpha]]
** [[Theropoda]]
</div>
}}
'''Dinosaurs''' were the dominant [[vertebrate]] animals of the [[Landform|terrestrial]] [[ecosystem]]s for over 160 million years, from the late [[Triassic]] [[Period (geology)|period]] (about 230&nbsp;[[Annum|million years ago]] to the end of the [[Cretaceous]] [[period]] (65&nbsp;million years ago). They are divided into a number of subgroups, the largest two being based on the structure of the hip. [[Saurischia]]ns retained the lizard-like hips of their ancestors, and included [[theropoda|theropods]] like ''[[Tyrannosaurus]]'' and [[sauropodomorpha|sauropodomorphs]] like ''[[Diplodocus]]''. [[Ornithischia]]ns were herbivores with bird-like hips, and included such groups as [[thyreophora|armored]], [[ceratopsia|horned]], [[pachycephalosauria|bone-headed]], and [[hadrosauridae|duck-billed dinosaurs]]. These groups evolved a variety of adaptations and occupied diverse niches as the Earth and its environments changed during the [[Mesozoic Era]], but (with the exception of their likely descendants, the [[bird]]s; see below), perished in the [[Cretaceous–Tertiary extinction event]] approximately 65 million years ago.

[[Dinosaur renaissance|Research since the 1970s]] has changed the scientific and public understanding of dinosaurs, from slow, unintelligent [[cold-blooded]] animals, to active animals with elevated metabolisms, often with adaptations for social interactions. One important component of the renewed interest in dinosaurs is their relationship with birds; research indicates that theropod dinosaurs are the most likely [[origin of birds|ancestors of birds]]. In fact, most paleontologists regard birds as the only surviving dinosaurs. [[Crocodilia]]ns are the other surviving close relatives of dinosaurs, and both groups are members of the [[Archosauria]], a group of [[reptiles]] that first appeared in the very late [[Permian]] and became dominant in the mid-Triassic.

Since the first dinosaur [[fossil]]s were recognized in the early nineteenth century, mounted dinosaur skeletons have become major attractions at museums around the world. Dinosaurs have become a part of world culture and remain consistently popular among children and adults. They have been featured in best-selling books and films (notably ''[[Jurassic Park]]''), and new discoveries are regularly covered by the [[News media|media]].

The term ''dinosaur'' is sometimes used informally to describe other prehistoric reptiles, such as the [[pelycosaur]] ''[[Dimetrodon]]'', the winged [[pterosaur]]s, and the aquatic [[ichthyosaur]]s, [[plesiosaur]]s and [[mosasaur]]s, although none of these were dinosaurs. In colloquial English "dinosaur" is sometimes used to to describe an obsolete or unsuccessful thing or person, despite the dinosaurs' 160 million&ndash;year reign and the global abundance and diversity of their descendants, the birds.

==What is a dinosaur?==
===Original definition===
The [[taxon]] '''Dinosauria''' was formally named in 1842 by [[English people|English]] [[palaeontology|palaeontologist]] [[Richard Owen]], who used 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>Owen, R. (1842). "Report on British Fossil Reptiles." Part II. Report of the British Association for the Advancement of Science, Plymouth, England.</ref> The term is derived from the [[Ancient Greek|Greek]] words δεινός (''deinos'' meaning "terrible", "fearsome", or "formidable") and σαύρα (''saura'' meaning "lizard" or "reptile"). Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it merely to evoke their size and majesty.<ref name=FBS97>{{cite book|author=Farlow, J.O., and Brett-Surman, M.K.|date=1997|title=Preface. In: Farlow, J.O., and Brett-Surman, M.K. (eds.). ''The Complete Dinosaur.''|publisher=Indiana University Press|pages= ix-xi|isbn=0-253-33349-0}}</ref>

===Modern definition===
[[Image:Triceratops AMNH 01.jpg|right|thumb|225px|''[[Triceratops]]'' [[skeleton]] at the [[American Museum of Natural History]] in New York City.]]
Under [[phylogenetics|phylogenetic taxonomy]], dinosaurs are usually defined as all descendants of the most recent common ancestor of ''[[Triceratops]]'' and modern [[birds]].<ref name="Irmis07">{{cite journal|author=Irmis, Randall B.|date=2007|title=A reappraisal of the phylogeny of early dinosaurs|journal=The Palaeontological Association Newsletter|volume=65|pages=92-94|url=http://socrates.berkeley.edu/~irmisr/sylbrad.pdf|accessdate=2007-11-22}}</ref> It has also been suggested that Dinosauria be defined as all of the descendants of the most recent common ancestor of ''[[Megalosaurus]]'' and ''[[Iguanodon]]'', because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria.<ref name="olshevsky2000">Olshevsky, G. (2000). "An annotated checklist of dinosaur species by continent." ''Mesozoic Meanderings'', '''3''': 1–157</ref> Both definitions result in the same set of animals being defined as dinosaurs, including [[theropoda|theropods]] (mostly [[bipedalism|bipedal]] [[carnivore]]s), [[sauropodomorpha|sauropodomorph]]s (mostly large [[herbivore|herbivorous]] [[quadruped]]s with long necks and tails), [[ankylosauria]]ns (armored herbivorous quadrupeds), [[stegosauria]]ns (plated herbivorous quadrupeds), [[ceratopsia]]ns (herbivorous quadrupeds with horns and frills), and [[ornithopoda|ornithopods]] (bipedal or quadrupedal herbivores including "duck-bills"). These definitions are written to correspond with scientific conceptions of dinosaurs that predate the modern use of phylogenetics. The continuity of meaning is intended to prevent confusion about what the term "dinosaur" means.

There is an almost universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict [[cladistics|cladistical]] definition that all descendants of a single common ancestor must be included in a group for that group to be natural, birds ''are'' dinosaurs and dinosaurs are, therefore, not extinct. Birds are classified by most paleontologists as belonging to the subgroup [[Maniraptora]], which are [[Coelurosauria|coelurosaurs]], which are theropods, which are [[saurischia]]ns, which are dinosaurs.<ref name=KP04>Padian, K. (2004). Basal Avialae. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). ''The Dinosauria'' (second edition). University of California Press:Berkeley, 210–231. ISBN 0-520-24209-2.</ref>

From the point of view of cladistics, birds are dinosaurs, but in ordinary speech the word "dinosaur" does not include birds. Additionally, referring to dinosaurs that are not birds as "non-avian dinosaurs" is cumbersome. For clarity, this article will use "dinosaur" as a synonym for "non-avian dinosaur". The term "non-avian dinosaur" will be used for emphasis as needed. It is also technically correct to refer to dinosaurs as a distinct group under the older [[Linnaean classification]] system, which accepts [[paraphyletic]] taxa that exclude some descendants of a single common ancestor.

===General description===
[[Image:Stego fieldmuseum.jpg|right|thumb|225px|''[[Stegosaurus]]'' skeleton, [[Field Museum]], [[Chicago]].]]
Using one of the above definitions, dinosaurs (aside from birds) can be generally described as terrestrial [[archosaur]]ian [[reptile]]s with [[terrestrial locomotion#Stance|limbs held erect beneath the body]], that existed from the [[Late Triassic]] (first appearing in the [[Carnian]] [[faunal stage]]) to the [[Late Cretaceous]] (going extinct at the end of the [[Maastrichtian]]).<ref name=DFG97>{{cite book |last=Glut |first=Donald F. |authorlink=Donald F. Glut |title=Dinosaurs: The Encyclopedia |year=1997 |publisher=McFarland & Co |location=Jefferson, North Carolina |pages=40 |isbn=0-89950-917-7}}</ref> Many prehistoric animals are popularly conceived of as dinosaurs, such as ichthyosaurs, mosasaurs, plesiosaurs, pterosaurs, and ''Dimetrodon'', but are not classified scientifically as dinosaurs. Marine reptiles like ichthyosaurs, mosasaurs, and plesiosaurs were neither terrestrial nor archosaurs; pterosaurs were archosaurs but not terrestrial; and ''Dimetrodon'' was a [[Permian]] animal more closely related to mammals.<ref name=DL90>{{cite book |last=Lambert |first=David |coauthors=and the Diagram Group |title=The Dinosaur Data Book |year=1990 |publisher=Avon Books |location=New York |isbn=0-380-75896-3 |pages=288}}</ref> Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the [[Jurassic]] and Cretaceous. Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a cat, and were generally rodent-sized carnivores of small prey.<ref name=MM97>{{cite book |last=Morales |first=Michael |editor=Farlow, James O.; and Brett-Surman, Michael K. (eds.) |title=The Complete Dinosaur |year=1997 |publisher=Indiana University Press |location=Bloomington |isbn=0-253-33349-0 |pages=607-624 |chapter=Nondinosaurian vertebrates of the Mesozoic }}</ref> One notable exception is ''[[Repenomamus|Repenomamus giganticus]]'', a [[triconodont]] weighing between {{kg to lb|12}} and {{kg to lb|14}} that is known to have eaten small dinosaurs like young ''[[Psittacosaurus]]''.<ref name=huetal2005>{{cite journal |author=Hu Yaoming |coauthors=Meng Jin; Wang Yuanqing; and Li Chuankui |year=2005 |title=Large Mesozoic mammals fed on dinosaurs |journal=Nature |volume=433 |pages=149–152|doi=10.1038/nature03102}}</ref>

Dinosaurs were an extremely varied group of animals; according to a 2006 study, over 500&nbsp;dinosaur genera have been identified with certainty so far, and the total number of genera preserved in the fossil record has been estimated at around&nbsp;1,850, nearly 75% of which remain to be discovered.<ref>{{cite journal|author=Wang, S.C., and Dodson, P. |date=2006|title=Estimating the Diversity of Dinosaurs|journal=Proceedings of the National Academy of Sciences USA|volume=103|issue=37|pages=13601–13605|pmid= 16954187}}</ref> An earlier study predicted that about 3,400&nbsp;dinosaur genera existed, including many which would not have been preserved in the fossil record.<ref name="russell1995">{{cite journal|author=Russell, Dale A.|date=1995|title=China and the lost worlds of the dinosaurian era|journal=Historical Biology|volume=10|pages=3-12}}</ref> Some were herbivorous, others carnivorous. Some dinosaurs were bipeds, some were quadrupeds, and others, such as ''[[Ammosaurus]]'' and ''[[Iguanodon]]'', could walk just as easily on two or four legs. Many had [[armour (zoology)|bony armor]], or cranial modifications like horns and crests. Although known for large size, many dinosaurs were human-sized or smaller. Dinosaur remains have been found on every continent on Earth, including [[Antarctica]].<ref name="MacLeod"/> Despite their diversity and dominance, however, dinosaurs (other than birds) did not spread into aquatic or aerial niches.

===Distinguishing features===
While recent discoveries have made it more difficult to present a universally agreed-upon list of dinosaurs' distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral [[archosaur]]ian skeleton. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical across Dinosauria; the earliest dinosaurs had them and passed them on to all their descendants. Such common features across a taxonomic group are called [[synapomorphy|synapomorphies]].

Dinosaur synapomorphies include an elongated crest on the [[humerus]], or upper arm bone, to accommodate the attachment of [[clavipectoral triangle|deltopectoral]] muscles; a shelf at the rear of the [[ilium (bone)|ilium]], or main hip bone; a [[tibia]], or shin bone, featuring a broad lower edge and a flange pointing out and to the rear; and an ascending projection on the [[talus bone|astragalus]], one of the ankle bones, which secures it to the tibia.<ref name=MJB04>{{cite book |last=Benton |first=Michael J. |authorlink=Michael J. Benton |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year=2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=7-19 |chapter=Origin and relationships of Dinosauria}}</ref>

[[Image:Edmontonia dinosaur.png|190px|left|thumb|''[[Edmontonia]]'' was an "armored dinosaur" of the group [[Ankylosauria]].]]
A variety of other skeletal features were shared by many dinosaurs. However, because they were either common to other groups of [[archosaurs]] or were not present in all early dinosaurs, these features are not considered to be synapomorphies. For example, as [[diapsid]] reptiles, dinosaurs ancestrally had two pairs of [[temporal 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>{{cite book|author=Holtz, Jr., T.R. |date=2000| title=Classification and evolution of the dinosaur groups. In: Paul, G.S. (ed.). ''The Scientific American Book of Dinosaurs.''|publisher=St. Martin's Press|pages=140–168|isbn=0-312-26226-4}}</ref> 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 [[vertebra]]e (three are found in some other archosaurs, but only two in are found in ''[[Herrerasaurus]]'');<ref name=MJB04/> and an [[acetabulum]], or hip socket, with a hole at the center of its inside surface (closed in ''[[Saturnalia (dinosaur)|Saturnalia]]'', for example).<ref name=LARB99>{{cite journal|author=Langer, M.C., Abdala, F., Richter, M., and Benton, M.J. |date=1999|title=A sauropodomorph dinosaur from the Upper Triassic (Carnian) of southern Brazil|journal=Comptes Rendus de l'Academie des Sciences, Paris: Sciences de la terre et des planètes|volume=329|pages=511–517}}</ref> Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the Late Triassic are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature.<ref name=NIP07>{{cite journal |last=Nesbitt |first=Sterling J. |coauthors= Irmis, Randall B.; and Parker, William G. |year=2007 |title=A critical re-evaluation of the Late Triassic dinosaur taxa of North America |journal=Journal of Systematic Palaeontology |volume=5 |issue=2 |pages=209-243 }}</ref>

Dinosaurs stood 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. Their posture was 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>{{cite book|author=Benton, M.J.|date=2004|title=Vertebrate Paleontology|publisher=Blackwell Publishers|pages=xii-452|isbn=0-632-05614-2}}</ref> Their erect posture enabled 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>{{cite book |last=Cowen |first=Richard |title=History of Life |edition=4th edition |chapter=Dinosaurs |publisher=Blackwell Publishing |isbn=1405117567 |pages=151-175}}</ref> Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs.<ref name=TKMB07>{{cite journal |last=Kubo |first |T. |coauthors=and Benton, M.J. |year=2007 |title=Evolution of hindlimb posture in archosaurs: limb stresses in extinct vertebrates |journal=Palaeontology |volume=50 |issue=6 |pages=1519-1529 }}</ref> 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/>

==Natural history==
===Origins and early evolution===
For a long time many scientists thought dinosaurs were [[polyphyletic]] with multiple groups of unrelated "dinosaurs" evolving due to similar pressures,<ref>{{ cite journal | author=Seeley, H.G. | date=1887 | title=On the classification of the fossil animals commonly named Dinosauria | journal=Proc R Soc London | publisher=[[Royal Society]] | volume=43 | pages=165-171 }}</ref><ref>{{ cite book | author=Romer, A.S. | date=1956 | title=Osteology of the Reptiles | publisher=University of Chicago }}</ref> but dinosaurs are now known to have formed a single group.<ref>{{cite journal | authors=Bakker, R. T., and Galton, P. | date=1974 | title=Dinosaur monophyly and a new class of vertebrates | journal=Nature | volume=248 | pages=168-172 | doi=10.1038/248168a0 | url=http://www.nature.com/nature/journal/v248/n5444/abs/248168a0.html}}</ref><ref name="MJB04" />

Dinosaurs diverged from their [[archosaur]] ancestors approximately 230&nbsp;million years ago during the Middle to Late [[Triassic]] period, roughly 20&nbsp;million years after the [[Permian-Triassic extinction event]] wiped out an estimated 95% of all [[life on Earth]].<ref>{{cite journal|author=Kump LR, Pavlov A & Arthur MA|title=Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia|journal=Geology|date=2005|volume=33|issue=5|pages=397-400|doi=10.1130/G21295.1}}</ref> <ref name="TannerLucas">{{cite journal|author=Tanner LH, Lucas SG & Chapman MG|title=Assessing the record and causes of Late Triassic extinctions|journal=Earth-Science Reviews|volume=65|issue=1-2|pages=103-139|date=2004|doi=10.1016/S0012-8252(03)00082-5|url=http://nmnaturalhistory.org/pdf_files/TJB.pdf|accessdate=2007-10-22}}</ref> [[Radiometric dating]] of the [[rock formation]] that contained fossils from the early dinosaur [[genus]] ''[[Eoraptor]]'' establishes its presence in the fossil record at this time. Paleontologists believe ''Eoraptor'' resembles the [[Common descent|common ancestor]] of all dinosaurs;<ref name="Sereno1999">{{cite journal|author=Sereno PC|title=The evolution of dinosaurs|date=1999|journal=Science|volume=284|issue=5423|pages=2137-2147|doi=10.1126/science.284.5423.2137}}</ref> if this is true, its traits suggest that the first dinosaurs were small, bipedal [[predation|predators]].<ref name=SFRM93>{{cite journal |last=Sereno |first=P.C. |authorlink=Paul Sereno |coauthors=Forster, C.A.; Rogers, R.R.; and Monetta, A.M. |year=1993 |title=Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria |journal=Nature |volume=361 |pages=64–66|doi=10.1038/361064a0}}</ref> The discovery of primitive, dinosaur-like [[ornithodiran]]s such as ''[[Marasuchus]]'' and ''[[Lagerpeton]]'' in [[Argentina|Argentinian]] [[Middle Triassic]] strata supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators.

When dinosaurs appeared, terrestrial habitats were occupied by various types of basal archosaurs and [[therapsida|therapsids]], such as [[aetosaur]]s, [[cynodont]]s, [[dicynodont]]s, [[ornithosuchidae|ornithosuchid]]s, [[rauisuchia]]s, and [[rhynchosaur]]s. Most of these other animals became extinct in the Triassic, in one of two events. First, at about the boundary between the [[Carnian]] and [[Norian]] [[faunal stage]]s (about 215&nbsp;million years ago), dicynodonts and a variety of basal [[archosauromorpha|archosauromorph]]s, including the [[prolacertiformes|prolacertiforms]] and rynchosaurs, became extinct. This was followed by the [[Triassic-Jurassic extinction event]] (about 200&nbsp;million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, [[phytosaur]]s, and rauisuchians. These losses left behind a land fauna of [[crocodylomorpha|crocodylomorph]]s, dinosaurs, [[mammal]]s, [[pterosauria]]ns, and [[turtle]]s.<ref name=MJB04/>

The first few lines of primitive dinosaurs [[Adaptive radiation|diversified]] through the [[Carnian]] and [[Norian]] [[faunal stage|stage]]s of the Triassic, most likely by occupying the niches of groups that became extinct. Traditionally, dinosaurs were thought to have [[Competition (biology)|replaced]] the variety of other Triassic land animals by proving superior through a long period of competition. This now appears unlikely, for several reasons. Dinosaurs do not show a pattern of steadily increasing in diversity and numbers, as would be predicted if they were competitively replacing other groups; instead, they were very rare through the Carnian, making up only 1-2% of individuals present in [[fauna]]s. In the Norian, however, after the extinction of several other groups, they became significant components of faunas, representing 50-90% of individuals. Also, what had been viewed as a key adaptation of dinosaurs, their erect stance, is now known to have present in several contemporaneous groups that were not as successful (aetosaurs, ornithosuchids, rauisuchians, and some groups of crocodylomorphs). Finally, the Late Triassic itself was a time of great upheaval in life, with shifts in plant life, marine life, and climate.<ref name="MJB04" />

===Classification===
{{main|Dinosaur classification}}

Dinosaurs (including birds) are [[archosaur]]s, like modern [[crocodilia]]ns. Archosaurs' [[diapsid]] skulls have two holes, called [[temporal fenestrae]], located where the jaw muscles attach, and an additional [[antorbital fenestra]] in front of the eyes. Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called [[synapsid]]s; and [[turtle]]s, with no temporal fenestra, are [[anapsid]]s. Anatomically, dinosaurs share many other archosaur characteristics, including teeth that grow from sockets rather than as direct extensions of the jawbones. 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 crocodylians sprawl out to either side.

Collectively, dinosaurs are usually regarded as a [[superorder]] or an unranked [[clade]]. They are divided into two [[Order (biology)|orders]], [[Saurischia]] and [[Ornithischia]], depending upon [[pelvis|pelvic]] structure. 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. Saurischians ('lizard-hipped', from the [[Ancient Greek|Greek]] ''sauros'' (''σαυρος'') meaning 'lizard' and ''ischion'' (''ισχιον'') meaning 'hip joint') retained the hip structure of their ancestors, with a [[pubis (bone)|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>{{cite book|last=Paul |first=G.S. |year=1988 |title=Predatory Dinosaurs of the World |location=New York |publisher=Simon and Schuster |pages=248-250 }}</ref> [[therizinosaur]]oids,<ref name="clarketal2004">Clark, J.M., Maryanska, T., and Barsbold, R. (2004). "Therizinosauroidea", in ''The Dinosauria'', 2nd ed. 151–164.</ref> [[dromaeosauridae|dromaeosaurids]],<ref name=MAPM04>Norell, M.A., and Makovicky, P.J. (2004). "Dromaeosauridae", in ''The Dinosauria'', 2nd ed. 196-210.</ref> and [[bird]]s<ref name=KP04/>). Saurischia includes the [[Theropoda|theropods]] (bipedal and mostly carnivores, except for birds) and [[Sauropodomorpha|sauropodomorphs]] (long-necked quadrupedal [[herbivore]]s).

By contrast, ornithischians ('bird-hipped', from the [[Ancient Greek|Greek]] ''ornitheios'' (''ορνιθειος'') meaning 'of a bird' and ''ischion'' (''ισχιον'') meaning 'hip joint') had a pelvis that superficially resembled a bird's pelvis: the [[pubis (bone)|pubis]] bone was oriented [[anatomical terms of location|caudally]] (rear-pointing). Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of herbivores. ('''NB:''' the terms "lizard hip" and "bird-hip" are misnomers &mdash; birds evolved from dinosaurs with "lizard hips".)

<center><gallery>
Image:Saurischia.png|[[Saurischia]]n pelvis structure (left side)
Image:Tyrannosaurus pelvis left.jpg|''[[Tyrannosaurus]]'' pelvis (showing saurischian structure - left side)
Image:Ornithischia.png|[[Ornithischia]]n pelvis structure (left side).
Image:Edmontosaurus pelvis left.jpg|''[[Edmontosaurus]]'' pelvis (showing ornithischian structure - left side)
</gallery></center>

The following is a simplified classification of dinosaur families. A more detailed version can be found at [[List of dinosaur classifications]].

[[Image:Struthiomimus altus jconway.jpg|thumb|300px|''[[Struthiomimus]]'', an ostrich-like [[theropod]] dinosaur.]]
*Dinosauria
:*[[Saurischia]] (theropods and sauropods)
::*[[Herrerasaur]]ians (early bipedal predators)
:::*[[Theropod]]s (all [[Bipedalism | bipedal]]; most were carnivores)
:::*[[Coelophysoidea|Coelophysoids]] (''[[Coelophysis]]'' and close relatives)
:::*[[Ceratosauria]]ns (''[[Ceratosaurus]]'' and [[abelisaur]]ids - the latter were important Late Cretaceous predators in southern continents)
:::*[[Spinosauroidea|Spinosauroids]] (long bodies, short arms, some with crocodile-like skulls and bony "sails" in their backs)
:::*[[Carnosauria]]ns (''[[Allosaurus]]'' and close relatives, like ''[[Carcharodontosaurus]]'')
:::*[[Coelurosauria]]ns (diverse, with a range of body sizes and niches)
::::*[[Tyrannosauroidea|Tyrannosauroids]] (small to gigantic, often with reduced forelimbs)
::::*[[Ornithomimosauria]]ns ("[[ostrich]]-mimics", toothless, carnivores to herbivores)
::::*[[Therizinosaur]]oids (bipedal herbivores with long arms and small heads)
::::*[[Oviraptorosauria]]ns (toothless; their diet and lifestyle are uncertain)
::::*[[Dromaeosauridae|Dromaeosaurids]] (like the "raptors" in ''[[Jurassic Park]]'')
::::*[[Troodontidae|Troodontids]] (similar to dromaeosaurids, but more lightly built, and possibly omnivorous)
::::*[[Aves|Birds]] (the only living dinosaurs)
[[Image:Brachiosaurus-brancai jconway.jpg|thumb|300px|''[[Brachiosaurus]]'' is an example of a [[sauropod]] dinosaur.]]
::*[[Sauropodomorpha|Sauropodomorphs]] (quadrupedal herbivores with small heads and long necks and tails, and elephant-like bodies)
:::*"[[Prosauropoda|Prosauropods]]" (early relatives of sauropods; small to quite large; some possibly omnivorous; bipeds and quadrupeds)
:::*[[Sauropoda|Sauropods]] (very large, usually over 15&nbsp;meters long [49&nbsp;ft])
::::*[[Diplodocoidea|Diplodocoids]] (skulls and tails elongated; teeth typically narrow and pencil-like)
::::*[[Macronaria]]ns (boxy skulls; spoon-shaped or pencil-shaped teeth)
:::::*[[Brachiosauridae|Brachiosaurids]] (very long necks; forelimbs longer than hindlimbs)
:::::*[[Titanosauria]]ns (diverse; stocky, with wide hips; most common in the Late Cretaceous of southern continents)
[[Image:Ornithopods jconway.jpg|300px|thumb|Various [[ornithopod]] dinosaurs and one [[heterodontosaurid]]. Far left: ''[[Camptosaurus]]'', left: ''[[Iguanodon]]'', center background: ''[[Shantungosaurus]]'', center foreground: ''[[Dryosaurus]]'', right: ''[[Corythosaurus]]'', far right (small): ''[[Heterodontosaurus]]'', far right (large) ''[[Tenontosaurus]]''.]]
:*[[Ornithischia]]ns (diverse bipedal and quadrupedal herbivores)
::*[[Heterodontosauridae|Heterodontosaurids]] (meter- or yard-scale herbivores or omnivores with prominent canine teeth)
::*[[Thyreophora]]ns (armored dinosaurs, mostly quadrupeds)
:::*[[Ankylosauria]]ns ([[scutes]] as primary armor; some had club-like tails)
:::*[[Stegosauria]]ns (spikes and plates as primary armor)
::*[[Ornithopoda|Ornithopods]] (diverse, from meter- or yard-scale bipeds to 12&nbsp;meter (39&nbsp;ft) animals that could moves as both bipeds and quadrupeds, evolved a method of chewing using skull flexibility and large numbers of teeth)
:::*[[Hadrosaur]]ids ("duckbilled dinosaurs")
::*[[Pachycephalosauria]]ns ("bone-heads", bipeds with domed or knobby growth on skulls)
::*[[Ceratopsia]]ns (dinosaurs with horns and frills, although most early forms had only the rudiments of these features)

===Evolution and paleobiogeography===
Dinosaur evolution after the Triassic follows changes in vegetation and the location of continents. In the Late Triassic and Early Jurassic, the continents were connected as the single landmass [[Pangaea]], there was a worldwide dinosaur fauna mostly composed of [[coelophysoidea|coelophysoid]] [[carnivore]]s and [[prosauropod]] [[herbivore]]s.<ref name=HCL04>{{cite book |last=Holtz |first=Thomas R., Jr. |coauthors=Chapman, Ralph E.; and Lamanna, Matthew C. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year=2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=627-642 |chapter=Mesozoic biogeography of Dinosauria}}</ref> [[Gymnosperm]] plants (particularly [[conifer]]s), a potential food source, radiated in the Late Triassic. Prosauropods did not have sophisticated mechanisms for processing food in the mouth, so must have employed other means of breaking down food farther along the digestive tract.<ref name=FS04>{{cite book |last=Fastovsky |first=David E. |coauthors=and Smith, Joshua B. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year=2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=614-626 |chapter=Dinosaur paleoecology}}</ref> The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of [[ceratosauria]]ns, [[spinosauroidea|spinosauroids]], and [[carnosauria]]ns, and herbivores consisting of [[stegosauria]]n ornithischians and large sauropods. Examples of this include the [[Morrison Formation]] of North America and [[Tendaguru|Tendaguru Beds]] of Tanzania. Dinosaurs in China show some differences, with specialized [[sinraptoridae|sinraptorid]] theropods and unusual, long-necked sauropods like ''[[Mamenchisaurus]]''.<ref name=HCL04/> [[Ankylosauria]]ns and [[ornithopoda|ornithopods]] were also becoming more common, but prosauropods had become extinct. Conifers and [[pteridophyte]]s were the most common plants. Sauropods, like the earlier prosauropods, 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 [[maniraptora]]n [[coelurosauria]]ns.<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, [[maniraptora]]n [[coelurosauria]]ns like [[dromaeosauridae|dromaeosaurids]], [[troodontidae|troodontid]]s, and [[oviraptorosauria]]ns became the common theropods, and [[ankylosauridae|ankylosaurids]] and early [[ceratopsia]]ns 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 [[angiosperm|flowering plants]]. 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 tooth batteries, taken to its extreme in [[hadrosaurid]]s.<ref name=FS04/> Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid ''[[Nigersaurus]]''.<ref name=serenoetal07>{{cite journal |last=Sereno |first=P.C. |coauthors=Wilson, J.A.; Witmer, L.M.; Whitlock, J.A.; Maga, A.; Ide, O.; and Rowe, T.A. |year=2007 |title=Structural extremes in a Cretaceous dinosaur |journal=PLoS ONE |volume=2 |issue=11 |pages=e1230 |url=http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0001230 |doi=10.1371/journal.pone.0001230}}</ref>

There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were [[tyrannosauridae|tyrannosaurid]]s and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and [[pachycephalosauria]]ns. In the southern continents that had made up the now-splitting [[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>{{cite journal |last=Prasad |first=V. |coauthors=Strömberg, C.A.E.; Alimohammadian, H; and Sahni, A. |year=2005 |title=Dinosaur coprolites and the early evolution of grasses and grazers |journal=Science |volume=310 |issue=5751 |pages=1170-1180 |doi=10.1126/science.1118806}}</ref> Grinding hadrosaurids and shearing ceratopsians became extremely diverse across North America and Asia. Theropods were also radiating as herbivores or omnivores, with [[therizinosaur]]ians and [[ornithomimosauria]]ns becoming common.<ref name=FS04/>

The [[Cretaceous–Tertiary extinction event]], which occurred approximately 65 million years ago at the end of the Cretaceous period, caused the extinction of all dinosaurs except for the line that had already given rise to the first birds. Some other [[diapsid]] groups, such as crocodylians, [[lizard]]s, [[snake]]s, [[sphenodontia]]ns, and [[choristodera]]ns, also survived the event.<ref name=AF04>{{cite book |last=Archibald |first=J. David |coauthors=and Fastovsky, David E. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year=2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=672–684 |chapter=Dinosaur Extinction}}</ref>

==Paleobiology==
Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including [[fossil]]ized [[bone]]s, [[feces]], [[trackway]]s, [[gastrolith]]s, [[feather]]s, impressions of skin, [[Viscus|internal organs]] and [[soft tissue]]s.<ref name="softtissue">{{cite journal|author=Dal Sasso, C. and Signore, M. |date=1998)|title=Exceptional soft-tissue preservation in a theropod dinosaur from Italy|journal=Nature|volume=292|issue=6674|pages=383–387|doi=10.1038/32884}}</ref><ref name="Schweitzer2005"/> Many fields of study contribute to our understanding of dinosaurs, including [[physics]] (especially [[biomechanics]]), [[chemistry]], [[biology]], and the [[earth sciences]] (of which [[paleontology]] is a sub-discipline). Two topics of particular interest and study have been dinosaur size and behavior.

===Size===
[[Image:Diplodocus size comparison.png|thumb|320px|Comparative size of ''[[Diplodocus]]''; human figures provide scale.]]
{{main|Dinosaur size}}

While the evidence is incomplete, it is clear that, as a group, dinosaurs were large. Even by dinosaur standards, the [[Sauropoda|sauropods]] were gigantic. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest were an [[order of magnitude]] more massive than anything else that has since walked the Earth. Giant prehistoric [[mammal]]s such as the ''[[Indricotherium]]'' and the Columbian [[mammoth]] were dwarfed by the giant sauropods, and only a handful of modern aquatic animals approach or surpass them in size &mdash; most notably the [[blue whale]], which reaches up to {{kg to lb|173000|precision=-3}} and over {{m to ft|30|precision=-1}} in length.<ref name=Cosewic>{{cite web|url=http://www.wildwhales.org/cetaceans/blue/sr_blue_whale_e.pdf.pdf|publisher=Committee on the Status of Endangered Wildlife in Canada|date=2002|title=Assessment and Update Status Report on the Blue Whale ''Balaenoptera musculus''|accessdate=2007-12-05}}</ref>

Most dinosaurs, however, were much smaller than the giant sauropods. Current evidence suggests that dinosaur average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods.<ref name="Sereno1999"/> Theropod dinosaurs, when sorted by estimated weight into categories based on [[order of magnitude]], most often fall into the 100 to 1,000&nbsp;kilogram (500 to 4,500&nbsp;lb) category, whereas [[Holocene|recent]] predatory [[carnivora]]ns peak in the 10 to 100&nbsp;kilogram (50 to 450&nbsp;lb) category.<ref name=JF93>{{cite book |last=Farlow |first=James A. |authorlink=James Farlow |year=1993 |title=Functional Morphology and Evolution |editors=Dodson, Peter; and Gingerich, Philip |series=American Journal of Science, Special Volume '''293-A''' |chapter=On the rareness of big, fierce animals: speculations about the body sizes, population densities, and geographic ranges of predatory mammals and large, carnivorous dinosaurs |pages=167-199}}</ref> A rough estimate for average dinosaur weight is about {{kg to lb|100|precision=-2}}. This contrasts sharply with the size of [[Cenozoic]] mammals, estimated by the same source (the [[National Museum of Natural History]]) as about 2 to 5&nbsp;kilograms (5 to 10&nbsp;lb).<ref name=NMNH>{{cite web |url=http://paleobiology.si.edu/dinosaurs/info/everything/evo_1.html |title=Anatomy and evolution |accessdate=2007-11-21 |publisher=National Museum of Natural History}}</ref>

====Largest and smallest====
Only a tiny percentage of animals ever fossilize, and most of these remain buried in the earth. Few of the 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. As a result, scientists will probably never be certain of the [[largest organism|largest and smallest dinosaurs]].

[[Image:Brachiosaurus scale.png|thumb|160px|right|Comparative size of ''[[Brachiosaurus]]''.]]
[[Image:Human-eoraptor size comparison(v2).png|thumb|140px|left|Comparative size of ''[[Eoraptor]]''.]]
The tallest and heaviest dinosaur known from good skeletons is ''[[Brachiosaurus|Brachiosaurus brancai]]'' (also known as ''[[Giraffatitan]]''). Its remains were discovered in [[Tanzania]] between 1907&ndash;12. Bones from multiple similarly-sized individuals were incorporated into the skeleton now mounted and on display at the [[Humboldt Museum]] of [[Berlin]];<ref name=EC68>Colbert, E.H. (1968). ''Men and Dinosaurs: The Search in Field and Laboratory.'' E. P. Dutton & Company:New York, vii + 283 p. ISBN 0140212884.</ref> this mount is {{m to ft|12}} tall and {{m to ft|22.5}} long, and would have belonged to an animal that weighed between 30,000 and 60,000&nbsp;kilograms (70,000 and 130,000&nbsp;lb). The longest complete dinosaur is the 27&nbsp;m (89&nbsp;ft) long ''[[Diplodocus]]'', which was discovered in [[Wyoming]] in the [[United States]] and displayed in [[Pittsburgh, Pennsylvania|Pittsburgh's]] [[Carnegie Natural History Museum]] in 1907.

There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest [[herbivore|herbivorous]] specimens on record were all discovered in the 1970s or later, and include the massive ''[[Argentinosaurus]]'', which may have weighed 80,000 to 100,000&nbsp;kilograms (90 to 110&nbsp;short tons); the longest, the {{m to ft|40|precision=-1}} long ''[[Supersaurus]]''; and the tallest, the {{m to ft|18}} ''[[Sauroposeidon]]'', which could have reached a sixth-floor window. The longest of them all may have been ''[[Amphicoelias|Amphicoelias fragillimus]]'', known only from a now lost partial vertebral [[neural arch]] described in 1878. Extrapolating from the illustration of this bone, the animal may have been {{m to ft|58}} long and weighed over {{kg to lb|120000|precision=-4}},<ref name=KC06>{{cite book |last=Carpenter |first=Kenneth |authorlink=Kenneth Carpenter |year=2006 |chapter=Biggest of the big: a critical re-evaluation of the mega-sauropod ''Amphicoelias fragillimus'' |editors=Foster, John R.; and Lucas, Spencer G. (eds.) |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |series=New Mexico Museum of Natural History and Science Bulletin, '''36''' |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque, New Mexico |pages=131-138 |url=https://scientists.dmns.org/sites/kencarpenter/PDFs%20of%20publications/Amphicoelias.pdf |format=pdf}}</ref> heavier than all known dinosaurs except possibly the poorly known ''[[Bruhathkayosaurus]]'', which could have weighed 175,000 to 220,000&nbsp;kilograms (400,000 to 500,000&nbsp;lb). The largest known [[carnivore|carnivorous]] dinosaur was ''[[Spinosaurus]]'', reaching a length of 16 to 18&nbsp;meters (50 to 60&nbsp;ft), and weighing in at {{kg to lb|8150|precision=-2}}.<ref name=SMBM06>dal Sasso, C., Maganuco, S., Buffetaut, E., and Mendez, M.A. (2006). New information on the skull of the enigmatic theropod ''Spinosaurus'', with remarks on its sizes and affinities. ''Journal of Vertebrate Paleontology'' '''25'''(4):888–896.</ref> Other large meat-eaters included ''[[Giganotosaurus]]'', ''[[Mapusaurus]]'', ''[[Tyrannosaurus rex]]'' and ''[[Carcharodontosaurus]]''.

Not including modern birds, the smallest dinosaurs known were about the size of a [[crow]] or a [[chicken]]. The theropods ''[[Microraptor]]'' and ''[[Parvicursor]]'' were both under 0.6&nbsp;meters (2&nbsp;ft) in length.

===Behavior===
[[Image:Maiasaurusnest.jpg|thumb|210px|A nesting ground of ''[[Maiasaura]]'' was discovered in 1978.]]

Interpretations of dinosaur behavior are generally based on the pose of body fossils and their [[Habitat (ecology)|habitat]], [[computer simulation]]s of their [[biomechanics]], and comparisons with modern animals in similar [[ecological niche]]s. As such, the current understanding of dinosaur behavior relies on speculation, and will likely remain controversial for the foreseeable future. However, there is general agreement that some behaviors which are common in crocodiles and birds, dinosaurs' closest living relatives, were also common among dinosaurs.

The first direct evidence of [[herd]]ing behavior was the 1878 discovery of 31&nbsp;''[[Iguanodon]]'' dinosaurs which were thought to have perished together in [[Bernissart]], [[Belgium]], after they fell into a deep, flooded [[sinkhole]] and drowned.<ref>{{cite journal|author=Yans J, Dejax J, Pons D, Dupuis C & Taquet P|date=2005|title=Implications paléontologiques et géodynamiques de la datation palynologique des sédiments à faciès wealdien de Bernissart (bassin de Mons, Belgique)|journal=Comptes Rendus Palevol|volume=4|issue=1-2|pages=135–150|language=French|doi=10.1016/j.crpv.2004.12.003}}</ref> Other mass death sites have been subsequently discovered. Those, along with multiple trackways, suggest that [[herd]] or [[Pack hunter|pack]] behavior was common in many dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that [[Hadrosaurid|duck-bills]] (hadrosaurids) may have moved in great herds, like the [[American Bison]] or the African [[Springbok Antelope|Springbok]]. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in [[Oxford]], England,<ref>{{cite journal |last=Day |first=J.J. |coauthors=and Upchurch, P. |year=2002 |title=Sauropod trackways, evolution, and behavior |journal=Science |volume=296 |pages=1659|doi=10.1126/science.107016}}</ref> and others kept their young in the middle of the herd for defense according to trackways at Davenport Ranch, [[Texas]]. Dinosaurs may have congregated in herds for defense, for [[Bird migration|migratory]] purposes, or to provide protection for their young. 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>{{cite book |last=Lessem |first=Don |coauthors=and Glut, Donald F. |year=1993 |title=The Dinosaur Society's Dinosaur Encyclopedia |chapter=''Allosaurus'' |pages=19–20|publisher=Random House|isbn=0-679-41770-2}}</ref><ref name="maxwell&ostrom1995">{{cite journal|last=Maxwell|first=W. D. |coauthors=Ostrom, J.H. |year=1995 |title=Taphonomy and paleobiological implications of ''Tenontosaurus''-''Deinonychus'' associations|journal=Journal of Vertebrate Paleontology |volume=15 |issue=4 |pages=707-712}}([http://www.vertpaleo.org/publications/jvp/15-707-712.cfm abstract])</ref> However, this lifestyle is uncommon among the modern relatives of dinosaurs ([[crocodile]]s and other reptiles, and [[bird]]s - [[Harris's Hawk]] is a well-documented exception), and the [[taphonomy|taphonomic]] evidence suggesting 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>{{cite journal|last=Roach|first=Brian T.|coauthors=and Brinkman, Daniel L. |year=2007 |title=A reevaluation of cooperative pack hunting and gregariousness in ''Deinonychus antirrhopus'' and other nonavian theropod dinosaurs|journal=Bulletin of the Peabody Museum of Natural History |volume=48 |issue=1 |pages=103–138}}</ref>
[[Image:Dino eggP9240092.JPG|thumb|right|Fossilized egg of the [[oviraptoridae|oviraptorid]] ''[[Citipati]]'', [[American Museum of Natural History]].]]
[[Jack Horner (paleontologist)|Jack Horner's]] 1978 discovery of a ''[[Maiasaura]]'' ("good mother dinosaur") [[nest]]ing ground in [[Montana]] demonstrated that parental care continued long after birth among the [[ornithopod]]s.<ref name=HM79>{{cite journal |last=Horner |first=J.R. |coauthors=and Makela, R. |year=1979 |title=Nest of juveniles provides evidence of family-structure among dinosaurs |journal=Nature |volume=282 |issue=5736 |pages=296–298}}</ref> There is also evidence that other Cretaceous-era dinosaurs, like [[Patagonia]]n [[titanosaur]]ian sauropods (1997 discovery), had similar nesting behaviors,<ref name=CCDJCF98>{{cite journal |last=Chiappe |first=L.M. |coauthors=Coria, R.A.; Dingus, L.; Jackson, F.; Chinsamy, A.; and Fox, M. |year=1998 |title=Sauropod dinosaur embryos from the Late Cretaceous of Patagonia |journal=Nature |volume=396 |pages=258-261}}</ref> and that the animals congregated in huge nesting colonies like those of [[penguin]]s. The [[Mongolia]]n [[oviraptoridae|oviraptorid]] ''[[Citipati]]'' was discovered in a [[chicken]]-like [[Avian incubation|brooding]] position in 1993, which may mean it was covered with an insulating layer of feathers that kept the [[egg (biology)|eggs]] warm.<ref>[http://search.eb.com/dinosaurs/dinosaurs/BRa.html Oviraptor nesting] ''[[Oviraptor]]'' nests or ''[[Protoceratops]]''?</ref> Parental care is also implied by other finds. For example, the fossilized remains of a grouping of ''[[Psittacosaurus]]'' has been found, consisting of one adult and 34 juveniles; in this case, the large number of juveniles may be due to communal nesting.<ref name=mengetal2004>{{cite journal |author=Meng Qingjin; Liu Jinyuan; Varricchio, David J.; Huang, Timothy; and Gao Chunling |year=2004 |title=Parental care in an ornithischian dinosaur |journal=Nature |volume=431 |pages=145–146}}</ref> Additionally, a dinosaur embryo (pertaining to the [[prosauropoda|prosauropod]] ''[[Massospondylus]]'') was found without teeth, indicating that some parental care was required to feed the young dinosaur.<ref name="Reiszetal05">{{cite journal| author =Reisz RR, Scott, D Sues, H-D, Evans, DC & Raath, MA| title =Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance| journal =Science| volume =309| issue =| pages =761–764| publisher =| location =| date =2005| url =| doi =10.1126/science.1114942| id =| accessdate =2007-10-24}}</ref> Trackways have also confirmed parental behavior among sauropods and ornithopods from the [[Isle of Skye]] in northwestern [[Scotland]].<ref>[http://news.bbc.co.uk/1/hi/scotland/3255494.stm Dinosaur family tracks] Footprints show maternal instinct after leaving the nest.</ref> Nests and eggs have been found for most major groups of dinosaurs, and it appears likely that dinosaurs communicated with their young, in a manner similar to modern birds and crocodiles.

[[Image:Centrosaurus dinosaur.png|thumb|left|225px|Artist's rendering of two ''[[Centrosaurus]]'', herbivorous [[ceratopsidae|ceratopsid]] dinosaurs from the late Cretaceous fauna of North America.]]
The [[Sagittal crest|crests]] and frills of some dinosaurs, like the [[marginocephalia]]ns, [[theropod]]s and [[lambeosaurine]]s, may have been too fragile to be used for active defense, 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>{{cite journal |last=Tanke |first=Darren H. |authorlink=Darren Tanke |coauthors=and Currie, Philip J. |year=1998 |title=Head-biting behavior in theropod dinosaurs: paleopathological evidence |journal=Gaia |issue=15 |pages=167–184 |url=http://www.mnhn.ul.pt/geologia/gaia/12.pdf |issn=0871-5424 |format=pdf}}</ref> The nature of dinosaur [[Animal communication|communication]] also remains enigmatic, and is an active area of research. For example, recent studies suggest that the hollow crests of the lambeosaurines may have functioned as [[resonance chamber]]s used for a wide range of [[Animal communication|vocalizations]].<ref name=JAH75>{{cite journal |last=Hopson |first=James A. |authorlink=James Hopson |year=1975 |title=The evolution of cranial display structures in hadrosaurian dinosaurs |journal=Paleobiology |volume=1 |issue=1 |pages=21-43 |url= |accessdate= }}</ref><ref name=DW98>{{cite journal |last=Diegert |first=Carl F. |coauthors=and Williamson, Thomas E. |year=1998 |title=A digital acoustic model of the lambeosaurine hadrosaur ''Parasaurolophus tubicen'' |journal=Journal of Vertebrate Paleontology |volume=18 |issue=3, Suppl. |pages=38A }}</ref>

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>{{cite web|url=http://www.amnh.org/exhibitions/fightingdinos/ex-fd.html|title=The Fighting Dinosaurs|publisher=American Museum of Natural History|accessdate=2007-12-05}}</ref> providing evidence that dinosaurs did indeed attack each other.<ref name=carpenter1998>{{cite journal |last=Carpenter |first=K. |authorlink=Kenneth Carpenter |year=1998 |title=Evidence of predatory behavior by theropod dinosaurs. |journal=Gaia |volume=15 |pages=135–144 |url=http://vertpaleo.org/publications/jvp/15-576-591.cfm|accessdate=2007-12-05}}</ref> 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>{{cite_journal |last=Rogers |first=Raymond R. |coauthors=Krause, David W.; & [[Kristina Curry Rogers|Curry Rogers, Kristina]]. |year=2007 |title=Cannibalism in the Madagascan dinosaur ''Majungatholus atopus'' |journal=Nature |volume=422 |issue=6931 |pages=515–518 |doi=10.1038/nature01532}}</ref>

Based on current fossil evidence from dinosaurs such as ''[[Oryctodromeus]]'', some herbivorous species seem to have led a partially [[fossorial]] (burrowing) lifestyle,<ref name=VMK07>{{cite journal |author=Varricchio DJ, Martin, AJ and Katsura, Y|year=2007 |title=First trace and body fossil evidence of a burrowing, denning dinosaur |journal=Proceedings of the Royal Society B: Biological Sciences |volume=274|issue=1616|pages=1361-1368 |doi=10.1098/rspb.2006.0443}}</ref> and some bird-like species may have been [[arboreal]] (tree-climbing), most notably primitive [[Dromaeosauridae|dromaeosaurids]] such as ''[[Microraptor]]''<ref name="chatterjee2007">{{cite journal |last=Chatterjee |first=S. |coauthors=and Templin, R.J. |year=2007 |title=Biplane wing planform and flight performance of the feathered dinosaur ''Microraptor gui'' |journal=Proceedings of the National Academy of Sciences |volume=104 |issue=5 |pages=1576-1580 |url=http://www.pnas.org/cgi/reprint/0609975104v1.pdf |format=pdf}}</ref> and the enigmatic [[scansoriopterygidae|scansoriopterygids]].<ref name="zhang2002">{{cite journal |author=Zhang, F.; Zhou, Z.; Xu, X.; and Wang, X. |year=2002 |title=A juvenile coelurosaurian theropod from China indicates arboreal habits |journal=Naturwissenschaften |volume=89 |issue=9 |pages=394-398 |doi=10.1007 /s00114-002-0353-8}}</ref> However, most 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]], in particular, 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>{{cite journal|author=Alexander RM|title=Dinosaur biomechanics|journal=Proceedings of the Royal Society of Biological Sciences|volume=273|issue=1596|date=2006|pages=1849-1855|doi=10.1098/rspb.2006.3532}}</ref> whether [[diplodocid]]s could create [[sonic boom]]s via [[whip]]-like tail snapping,<ref>{{cite journal|author=Goriely A & McMillen T|title=Shape of a cracking whip|date=2002|journal=Physical Review Letters|volume=88|issue=24|pages=244301|doi=10.1103/PhysRevLett.88.244301}}</ref> and whether sauropods could float.<ref>{{cite journal|author=Henderson, D.M.|date=2003|title=Effects of stomach stones on the buoyancy and equilibrium of a floating crocodilian: A computational analysis.|journal=Canadian Journal of Zoology|volume=81|issue=8|pages=1346–1357|doi=10.1139/z03-122}}</ref>

===Physiology===
{{main|Physiology of dinosaurs}}
[[Image:Palais de la Decouverte Tyrannosaurus rex p1050042.jpg|210px|thumb|right|''[[Tyrannosaurus rex]]'' skull and upper vertebral column, Palais de la Découverte, Paris.]]
A vigorous debate on the subject of temperature regulation in dinosaurs has been ongoing since the 1960s. Originally, scientists broadly disagreed as to whether dinosaurs were capable of regulating their body temperatures at all. More recently, dinosaur [[Warm-blooded|endotherm]] has become the consensus view, and debate has focused on the mechanisms of temperature regulation.

After dinosaurs were discovered, paleontologists first posited that they were [[ectotherm]]ic creatures: "terrible [[lizard]]s" as their name suggests. This supposed cold-bloodedness implied that dinosaurs were relatively slow, sluggish organisms, comparable to modern reptiles, which need external sources of heat in order to regulate their body temperature. Dinosaur ectothermy remained a prevalent view until [[Robert T. Bakker|Robert T. "Bob" Bakker]], an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968.

Modern evidence indicates that dinosaurs thrived in cooler temperate climates, and that at least some dinosaur species must have regulated their body temperature by internal biological means (perhaps aided by the animals' bulk). Evidence of [[Warm-blooded|endotherm]] in dinosaurs includes the discovery of [[polar dinosaurs in Australia]] and [[Antarctica]] (where they would have experienced a cold, dark six-month winter), the discovery of dinosaurs whose feathers may have provided regulatory insulation, and analysis of blood-vessel structures that are typical of endotherms within dinosaur bone. Skeletal structures suggest that theropods and other dinosaurs had active lifestyles better suited to an endothermic cardiovascular system, while sauropods exhibit fewer endothermic characteristics. It is certainly possible that some dinosaurs were endothermic while others were not. Scientific debate over the specifics continues.<ref>Parsons, K.M. (2001). ''Drawing Out Leviathan''. Indiana University Press. 22–48. ISBN 0-253-33937-5.</ref>

Complicating the debate is the fact that warm-bloodedness can emerge based on more than one mechanism. Most discussions of dinosaur endothermy tend to compare them to average birds or mammals, which expend energy to elevate body temperature above that of the environment. Small birds and mammals also possess [[thermal insulation|insulation]], such as [[fat]], [[fur]], or [[feather]]s, which slows down heat loss. However, large mammals, such as elephants, face a different problem because of their relatively small ratio of surface area to volume ([[J. B. S. Haldane|Haldane's]] principle). This ratio compares the volume of an animal with the area of its skin: as an animal gets bigger, its surface area increases more slowly than its volume. At a certain point, the amount of heat radiated away through the skin drops below the amount of heat produced inside the body, forcing animals to use additional methods to avoid overheating. In the case of elephants, they are hairless, and have large ears which increase their surface area, and have behavioral adaptations as well (such as using the trunk to spray water on themselves and mud wallowing). These behaviors increase cooling through evaporation.

Large dinosaurs would presumably have had to deal with similar issues; their body size suggest they lost heat relatively slowly to the surrounding air, and so could have been what are called [[gigantothermy|inertial homeotherms]], animals that are warmer than their environments through sheer size rather than through special adaptations like those of birds or mammals. However, so far this theory fails to account for the numerous dog- and goat-sized dinosaur species, or the young of larger species.

Modern [[computerized tomography]] (CT) scans of a [[Thescelosaurus|dinosaur]]'s chest cavity (conducted in 2000) found the apparent remnants of a four-chambered heart, much like those found in today's mammals and birds.<ref>{{cite journal|author=Fisher, P. E., Russell, D. A., Stoskopf, M. K., Barrick, R. E., Hammer, M. & Kuzmitz, A. A.|date=2000|title=Cardiovascular evidence for an intermediate or higher metabolic rate in an ornithischian dinosaur|journal=Science|volume=288|issue=5465|pages=503–505|doi=10.1126/science.288.5465.503}}</ref> The idea is controversial within the scientific community, coming under fire for bad anatomical science<ref>{{cite journal|author=Hillenius, W. J. & Ruben, J. A.|date=2004|title=The evolution of endothermy in terrestrial vertebrates: Who? when? why?|journal=Physiological and Biochemical Zoology|volume=77|issue=6|pages=1019–1042|doi=10.1086/425185}}</ref> or simply wishful thinking.<ref>{{cite journal|title=Dinosaur with a Heart of Stone|author=Rowe T, McBride EF, & Sereno PC |date=2001 |journal=Science |volume=291 |issue=5505 |pages=783 |doi=10.1126/science.291.5505.783a}}</ref> The question of how this find reflects on metabolic rate and dinosaur internal anatomy may be moot, though, regardless of the object's identity: both modern [[crocodilia]]ns and [[bird]]s, the closest living relatives of dinosaurs, have four-chambered hearts (albeit modified in crocodilians), so dinosaurs probably had them as well.<ref name=CH04>Chinsamy, Anusuya; and Hillenius, Willem J. (2004). "Physiology of nonavian dinosaurs". ''The Dinosauria'', 2nd. 643–659.</ref>

===Soft tissue and DNA===
One of the best examples of soft tissue impressions in a fossil dinosaur was discovered in [[Petraroia]], [[Italy]]. The discovery was reported in 1998, and described the specimen of a small, very young [[coelurosaur]], ''[[Scipionyx]] samniticus''. The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this immature dinosaur.<ref name="softtissue" />

In the March 2005 issue of ''[[Science (journal)|Science]]'', [[Mary Higby Schweitzer|Dr. Mary Higby Schweitzer]] and her team announced the discovery of flexible material resembling actual soft tissue inside a 68-million-year-old ''[[Tyrannosaurus rex]]'' leg [[bone]] from the [[Hell Creek Formation]] in [[Montana]]. After recovery, the tissue was rehydrated by the science team.<ref name="Schweitzer2005"/>

When the fossilized bone was treated over several weeks to remove mineral content from the fossilized bone marrow cavity (a process called demineralization), Schweitzer found evidence of intact structures such as [[blood vessel]]s, bone matrix, and connective tissue (bone fibers). Scrutiny under the microscope further revealed that the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. The exact nature and composition of this material, and the implications of Dr. Schweitzer's discovery, are not yet clear; study and interpretation of the material is ongoing.<ref name="Schweitzer2005">{{cite journal|author=Schweitzer, M.H., Wittmeyer, J.L. and Horner, J.R.|date=2005|title=Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex|journal=Science|volume=307|issue=5717|pages=1952–1955|doi=10.1126/science.1108397}}</ref>

The successful extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions, but upon further inspection and [[peer review]], neither of these reports could be confirmed.<ref>{{cite journal|author=Wang, H., Yan, Z. and Jin, D.|date=1997|title=Reanalysis of published DNA sequence amplified from Cretaceous dinosaur egg fossil|journal=Molecular Biology and Evolution|volume=14|pages=589–591|url=http://mbe.oupjournals.org/cgi/reprint/14/5/589|accessdate=2007-12-05}}</ref> However, a functional visual [[peptide]] of a theoretical dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of related modern species such as reptiles and birds.<ref>{{cite journal|author=Chang BS, Jönsson K, Kazmi MA, Donoghue MJ, Sakmar TP|date=2002|title=Recreating a Functional Ancestral Archosaur Visual Pigment|journal=Molecular Biology and Evolution|volume=19|issue=9|pages=1483–1489|pmid=12200476|url=http://mbe.oxfordjournals.org/cgi/content/full/19/9/1483|accessdate=2007-12-05}}</ref> In addition, several [[protein]]s have putatively been detected in dinosaur fossils,<ref>{{cite journal|author=Embery G, Milner AC, Waddington RJ, Hall RC, Langley MS, Milan AM|title=Identification of proteinaceous material in the bone of the dinosaur Iguanodon|journal=Connect Tissue Res|date=2003|volume=44|issue=Suppl 1|pages=41-6|pmid=12952172}}</ref> including hemoglobin.<ref>{{cite journal|author=Schweitzer MH, Marshall M, Carron K, Bohle DS, Busse SC, Arnold EV, Barnard D, Horner JR, Starkey JR|title=Heme compounds in dinosaur trabecular bone|journal=Proc Natl Acad Sci U S A.|date=1997|volume=94|issue=12|pages=6291–6|pmid=9177210}}</ref>

Even if dinosaur DNA could be reconstructed, it would be exceedingly difficult to clone and "grow" dinosaurs using current technology since no closely related species exist to provide [[zygote]]s or a suitable environment for [[Embryogenesis|embryonic development]].

==Feathers and the 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>{{cite_journal |last=Huxley |first=Thomas H. |authorlink=Thomas Henry Huxley |year=1868 |title=On the animals which are most nearly intermediate between birds and reptiles |journal=Annals of the Magazine of Natural History |volume=4 |issue=2 |pages=66-75}}</ref> After the work of [[Gerhard Heilmann]] in the early 20th century, the theory of birds as dinosaur descendants was abandoned in favor of generalized [[thecodont]] ancestors, with the key piece of evidence being the supposed lack of [[clavicle]]s in dinosaurs.<ref name=heilmann>{{cite_book |last=Heilmann |first=Gerhard |year=1926 |title=The Origin of Birds |location=London |publisher=Witherby |pages=208pp}}</ref> 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>{{cite journal |last=Osborn |first=Henry Fairfield |year=1924 |title=Three new Theropoda, ''Protoceratops'' zone, central Mongolia |journal=American Museum Novitates |volume=144 |pages=1-12 |url=http://digitallibrary.amnh.org/dspace/bitstream/2246/3223/1/N0144.pdf |format=pdf}}</ref> In the 1970s, [[John Ostrom]] revived the dinosaur-bird theory,<ref name=ostrom1973>{{cite_journal |last=Ostrom |first=John H. |authorlink=John Ostrom |year=1973 |title=The ancestry of birds |journal=Nature |volume=242 |issue=5393 |pages=136 |doi=10.1038/242136a0}}</ref> which gained momentum in the coming decades with the advent of cladistic analysis,<ref name=gauthier1986>{{cite_book |last=Gauthier |first=Jacques. |authorlink=Jacques Gauthier |year=1986 |chapter=Saurischian monophyly and the origin of birds |editor=Padian, Kevin. (ed.) |title=The Origin of Birds and the Evolution of Flight |series=Memoirs of the California Academy of Sciences '''8''' |pages=1-55}}</ref> and a great increase in the discovery of small theropods and early birds.<ref name=TRHJ00/> Of particular note has been the fossils of the [[Yixian Formation]], where a variety of theropods and early birds have been found, often with feathers of some type.<ref name=KP04/> Birds share over a hundred distinct anatomical features with theropod dinosaurs, which are now generally accepted to have been their closest ancient relatives.<ref>{{cite journal|author=Mayr, G., Pohl, B. and Peters, D.S.|date=2005|title=A Well-Preserved Archaeopteryx Specimen with Theropod Features|journal=Science|volume=310|issue=5753|pages=1483-1486|doi=10.1126/science.1120331}}</ref>
They are most closely allied with [[maniraptora]]n 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>{{cite_journal |last=Martin |first=Larry D. |authorlink=Larry Martin |year=2006 |title=A basal archosaurian origin for birds |journal=Acta Zoologica Sinica |volume=50 |issue=6 |pages=977-990}}</ref> or that maniraptoran theropods are the ancestors of birds but themselves are not dinosaurs, only [[convergent evolution|convergent]] with dinosaurs.<ref name=AF02>{{cite journal |last=Feduccia |first=A. |year=2002 |title=Birds are dinosaurs: simple answer to a complex problem |journal=The Auk |volume=119 |pages=1187-1201}}</ref>

===Feathers===
{{main|Feathered dinosaurs}}
[[Image:SArchaeopteryxBerlin2.jpg|thumb|210px|right|The famous Berlin Specimen of ''[[Archaeopteryx|Archaeopteryx lithographica]]''.]]

''[[Archaeopteryx]]'', the first good example of a "feathered dinosaur", was discovered in 1861. The initial specimen was found in the [[Solnhofen limestone]] in southern Germany, which is a ''[[Lagerstätten|lagerstätte]]'', a rare and remarkable geological formation known for its superbly detailed fossils. ''Archaeopteryx'' is a [[transitional fossil]], with features clearly intermediate between those of modern reptiles and birds. Brought to light just two years after Darwin's seminal ''[[The Origin of Species]]'', 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 ''[[Compsognathus]]''.<ref name=PW88>{{cite journal|author=Wellnhofer, P|date=1988|title=Ein neuer Exemplar von ''Archaeopteryx''|journal=Archaeopteryx|volume=6|pages=1–30}}</ref>

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. Most of these specimens were unearthed in the [[Lagerstätten|lagerstätte]] of the Yixian Formation, [[Liaoning]], northeastern [[China]], which was part of an island continent during the Cretaceous. Though feathers have been found only in a few locations, it is possible that non-avian dinosaurs elsewhere in the world were also feathered. The lack of widespread fossil evidence for feathered non-avian dinosaurs may be due to the fact that delicate features like skin and feathers are not often preserved by [[fossil]]ization and thus are absent from the fossil record. To this point, protofeathers (thin, filament-like structures) are known from dinosaurs at the base of Coelurosauria, such as [[compsognathidae|compsognathids]] like ''[[Sinosauropteryx]]'' and [[tyrannosauroidea|tyrannosauroids]] (''[[Dilong (dinosaur)|Dilong]]''),<ref>{{cite journal|author=Xu X.; Norell, M.A.; Kuang X.; Wang X.; Zhao Q.; and Jia C.|title=Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids|journal=Nature|date=2004|volume=431|issue=7009|pages=680-684|pmid=15470426}}</ref> but barbed feathers are only known among the coelurosaur subgroup Maniraptora, which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds.<ref name=KP04/><ref name=GC06>{{cite journal |last=Göhlich |first=U.B. |coauthors=and Chiappe, L.M. |year=2006 |title=A new carnivorous dinosaur from the Late Jurassic Solnhofen archipelago |journal=Nature |volume=440 |pages= 329-332}}</ref> The description of feathered dinosaurs has not been without controversy; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that protofeathers are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' integument,<ref name=TLS03>{{cite journal |last=Lingham-Soliar |first=T. |year=2003 |title=The dinosaurian origin of feathers: perspectives from dolphin (Cetacea) collagen fibers |journal= Naturwissenschaften |volume=90 |volume=12 |pages=563-567 |pmid=14676953}}</ref><ref name=FLH05>{{cite journal|last=Feduccia |first=A. |coauthors=Lingham-Soliar, T.; and Hinchliffe, J.R. |year=2005 |title=Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence |journal=Journal of Morphology |volume=266 |issue=2 |pages=125-166 |pmid=16217748}}</ref><ref name=LSFX07>{{cite journal |last=Lingham-Soliar |first=T. |coauthors=Feduccia, A.; and Wang X. |year=2007 |title=A new Chinese specimen indicates that 'protofeathers' in the Early Cretaceous theropod dinosaur ''Sinosauropteryx'' are degraded collagen fibres |journal=Proceedings of the Biological Sciences |volume=274 |issue=1620 |pages=1823-9 |pmid=17521978}}</ref> and that maniraptoran dinosaurs with barbed feathers were not actually dinosaurs, but [[convergent evolution|convergent]] with dinosaurs.<ref name=AF02>{{cite journal |last=Feduccia |first=A. |year=2002 |title=Birds are dinosaurs: simple answer to a complex problem |journal=The Auk |volume=119 |pages=1187-1201}}</ref><ref name=FLH05/> However, their views have for the most part not been accepted by other researchers, to the point that the question of the scientific nature of Feduccia's proposals has been raised.<ref>{{cite journal |last=Prum |first=Richard O. |month=April |year=2003 |title=Are Current Critiques Of The Theropod Origin Of Birds Science? Rebuttal To Feduccia 2002 |journal=[[The Auk]] |volume=120 |issue=2 |pages=550–61 |url=http://links.jstor.org/sici?sici=0004-8038(200304)120:2%3C550:ACCOTT%3E2.0.CO;2-0}}</ref>

===Skeleton===
Because feathers are often associated with birds, feathered dinosaurs are often touted as the [[transitional fossil|missing link]] between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent another important line of evidence for [[paleontologist]]s. Areas of the skeleton with important similarities include the neck, [[pubis (bone)|pubis]], [[wrist]] (semi-lunate [[carpal]]), arm and [[pectoral girdle]], furcula (wishbone), and [[keel (bird)|breast bone]]. Comparison of bird and dinosaur skeletons through [[cladistics|cladistic analysis]] strengthens the case for the link.

[[Image:sue in nyc dino trex.jpg|thumb|210px|left|[[Theropod]]s, a diverse group of carnivorous dinosaurs that included ''[[Tyrannosaurus rex]]'', are generally accepted to have been birds' closest relatives.]]

===Soft anatomy===
Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to an investigation which was led by [[Patrick O'Connor (paleontologist)|Patrick O'Connor]] of [[Ohio University]]. The lungs of theropod dinosaurs (carnivores that walked on two legs and had birdlike feet) likely pumped air into hollow sacs in their [[skeleton]]s, 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>{{cite journal|author=O'Connor PM & Claessens LPAM|date=2005|title=Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs|journal=Nature|volume=436|pages=253-256|doi=10.1038/nature03716}}</ref>

Another piece of evidence that birds and dinosaurs are closely related is the use of [[gizzard]] stones. These stones are swallowed by animals to aid digestion and break down food and hard fibres once they enter the stomach. When found in association with [[fossil]]s, gizzard stones are called [[gastrolith]]s.<ref>{{cite journal|author=Wings O|title=A review of gastrolith function with implications for fossil vertebrates and a revised classification|journal=Palaeontologica Polonica|volume=52|issue=1|pages=1–16|date=2007|url=http://www.app.pan.pl/acta52/app52-001.pdf|accessdate=2007-11-24}}</ref>

===Reproductive biology===
A discovery of features in a ''[[Tyrannosaurus rex]]'' [[skeleton]] recently provided more evidence that dinosaurs and birds evolved from a common ancestor and, for the first time, allowed paleontologists to establish the sex of a dinosaur. When laying eggs, female birds grow a special type of bone in their limbs between the hard outer bone and the [[marrow]]. This ''medullary'' bone, which is rich in [[calcium]], is used to make eggshells. The presence of endosteally-derived bone tissues lining the interior marrow cavities of portions of the ''Tyrannosaurus rex'' specimen's hind limb suggested that ''T. rex'' used similar reproductive strategies, and revealed the specimen to be female.<ref name="schweitzeretal2005">{{cite journal | last=Schweitzer |first=M.H. |coauthors=Wittmeyer, J.L.; and Horner, J.R. |y ear=2005 | title=Gender-specific reproductive tissue in ratites and ''Tyrannosaurus rex'' | journal=Science | volume=308 | pages=1456–1460| url=http://www.sciencemag.org/cgi/content/abstract/308/5727/1456 | doi=10.1126/science.1112158}}</ref> Further research has found medullary bone in the theropod ''[[Allosaurus]]'' and 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 dinosaurs in general produced medullary tissue. Medullary bone has been found in specimens of sub-adult size, which suggests that dinosaurs reached sexual maturity rather quickly for such large animals.<ref name=LW08>{{cite journal |last=Lee |first=Andrew H. |coauthors=and Werning, Sarah |year=2008 |title=Sexual maturity in growing dinosaurs does not fit reptilian growth models |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=2 |pages=582-587 |doi=10.1073/pnas.0708903105 | url=http://www.pnas.org/cgi/content/abstract/105/2/582 }}</ref>
[[Image:Amnh30.jpg|thumb|right|210px|Model of ''[[Microraptor]]'', a four-winged dinosaur with long [[pennaceous feather]]s.]]

===Behavioral evidence===
A recently discovered [[Troodontidae|troodont]] fossil demonstrates that the dinosaurs slept like certain modern birds, with their heads tucked under their arms.<ref>{{cite journal|author=Xu, X. and Norell, M.A.|date=2004|title=A new troodontid dinosaur from China with avian-like sleeping posture|journal=Nature|volume=431|pages=838-841|doi=10.1038/nature02898}}</ref> This behavior, which may have helped to keep the head warm, is also characteristic of modern birds.

==Extinction==
{{main|Cretaceous–Tertiary extinction event}}
{{main|K–T boundary}}

Non-avian dinosaurs suddenly became [[extinct]] approximately 65&nbsp;million years ago. Many other groups of animals also became extinct at this time, including [[ammonite]]s ([[nautilus]]-like [[mollusk]]s), [[mosasaur]]s, plesiosaurs, pterosaurs, herbivorous [[turtle]]s and [[crocodile]]s, most birds, and many groups of mammals.<ref name="MacLeod">{{cite journal|author=MacLeod, N, Rawson, PF, Forey, PL, Banner, FT, Boudagher-Fadel, MK, Bown, PR, Burnett, JA, Chambers, P, Culver, S, Evans, SE, Jeffery, C, Kaminski, MA, Lord, AR, Milner, AC, Milner, AR, Morris, N, Owen, E, Rosen, BR, Smith, AB, Taylor, PD, Urquhart, E & Young, JR|title=The Cretaceous–Tertiary biotic transition|date=1997|journal=Journal of the Geological Society|volume=154|issue=2|pages=265–292|url=http://findarticles.com/p/articles/mi_qa3721/is_199703/ai_n8738406/print}}</ref> This [[mass extinction]] is known as the [[Cretaceous–Tertiary extinction event]]. The nature of the event that caused this mass extinction has been extensively studied since the 1970s; at present, several related theories are supported by paleontologists. Though the general consensus is that an impact event was the primary cause of dinosaur extinction, some scientists cite other possible causes, or support the idea that a confluence of several factors was responsible for the sudden disappearance of dinosaurs from the fossil record.

At the peak of the dinosaur era, there were no [[polar ice cap]]s, and sea levels are estimated to have been from 100 to 250&nbsp;meters (300 to 800&nbsp;ft) higher than they are today. The planet's temperature was also much more uniform, with only 25&nbsp;°[[Celsius|C]] (45&nbsp;°[[Fahrenheit|F]]) separating average polar temperatures from those at the equator. On average, atmospheric temperatures were also much warmer; the poles, for example, were 50&nbsp;°C (90&nbsp;°F) warmer than today.<ref name="pmid16311326">{{cite journal |author=Miller KG, Kominz MA, Browning JV, Wright JD, Mountain GS, Katz ME, Sugarman PJ, Cramer BS, Christie-Blick N, Pekar SF |title=The Phanerozoic record of global sea-level change |journal=Science |volume=310 |issue=5752 |pages=1293–8 |year=2005 |pmid=16311326 |doi=10.1126/science.1116412}}</ref><ref>{{cite journal|title=Palaeotemperatures, polar ice-volume, and isotope stratigraphy (Mg/Ca, δ18O, δ13C, 87Sr/86Sr): The Early Cretaceous (Berriasian, Valanginian, Hauterivian)|author=McArthura JM, Janssenb NMM, Rebouletc S, Lengd MJ, Thirlwalle MF & van de Shootbruggef B|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=248|issues=3-4|date=2007|pages=391-430|doi=doi:10.1016/j.palaeo.2006.12.015}}</ref>

The atmosphere's composition during the dinosaur era was vastly different as well. Carbon dioxide levels were up to 12&nbsp;times higher than today's levels, and oxygen formed 32 to 35%&nbsp;of the atmosphere, as compared to 21%&nbsp;today. However, by the late [[Cretaceous]], the environment was changing dramatically. Volcanic activity was decreasing, which led to a cooling trend as levels of atmospheric carbon dioxide dropped. Oxygen levels in the atmosphere also started to fluctuate and would ultimately fall considerably. Some scientists hypothesize that climate change, combined with lower oxygen levels, might have led directly to the demise of many species. If the dinosaurs had respiratory systems similar to those commonly found in modern birds, it may have been particularly difficult for them to cope with reduced respiratory efficiency, given the enormous oxygen demands of their very large bodies.<ref name="MacLeod"/>

===Impact event===
[[Image:Chicxulub radar topography.jpg|thumb|The [[Chicxulub Crater]] at the tip of the [[Yucatán Peninsula]], the impact of which may have caused the dinosaur extinction.]]
The asteroid collision theory, which was first proposed by [[Walter Alvarez]] in the late 1970s, links the [[extinction event]] at the end of the Cretaceous period to a [[bolide]] impact approximately 65.5&nbsp;million years ago. Alvarez proposed that a sudden increase in [[iridium]] levels, recorded around the world in the period's rock stratum, was direct evidence of the impact. The bulk of the evidence now suggests that a 5 to 15&nbsp;kilometer (3 to 9&nbsp;mi) wide [[Meteoroid#Bolide|bolide]] hit in the vicinity of the [[Yucatán Peninsula]], creating the {{km to mi|170|precision=-1}} wide [[Chicxulub Crater]] and triggering the [[mass extinction]]. Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave.

Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun).

In September of 2007, U.S. researchers led by [[William Bottke]] of the [[Southwest Research Institute]] in [[Boulder, Colorado]], and [[Czech Republic|Czech]] scientists used [[computer]] simulations to identify the probable source of the Chicxulub impact. They calculated a 90% probability that a giant asteroid named [[Baptistina]], approximately {{km to mi|160|precision=-1}} in diameter, orbiting in the asteroid belt which lies between [[Mars]] and [[Jupiter]], was struck by a smaller unnamed asteroid about 55 kilometers (35 mi) in diameter about 160&nbsp;million years ago. The impact shattered Baptistina, creating a cluster which still exists today as the [[Baptistina family]]. Calculations indicate that some of the fragments were sent hurtling into earth-crossing orbits, one of which was the {{km to mi|10}} wide [[meteorite]] which struck [[Mexico]]'s [[Yucatan]] [[peninsula]] 65&nbsp;million years ago, creating the [[Chicxulub crater]] ({{km to mi|175|precision=-1}}).

While similar to Alvarez's impact theory (which involved a single asteroid or comet), this theory proposes that "passages of the [[Oort cloud#Star perturbations and Nemesis theory|solar companion star Nemesis]] through the [[Oort cloud|Oort comet cloud]] would trigger comet showers."<ref name="Koeberl">{{cite book|Koeberl, C & MacLeodKG|date=2002|title=Catastrophic Events and Mass Extinctions|publisher=Geological Society of America|isbn=0-8137-2356-6}}</ref> One or more of these objects then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period.<ref name="Koeberl"/>

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

Before 2000, arguments that the [[Deccan Traps]] [[flood basalt]]s caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68&nbsp;mya and lasted for over 2 million years. However, there is evidence that two-thirds of the Deccan Traps were created in 1 million years about 65.5&nbsp;mya, so these eruptions would have caused a fairly rapid extinction, possibly a period of thousands of years, but still a longer period than what would be expected from a single impact event.<ref>{{cite journal|author=Hofman, C, Féraud, G & Courtillot, V|date=2000|title=40Ar/39Ar dating of mineral separates and whole rocks from the Western Ghats lava pile: further constraints on duration and age of the Deccan traps|journal=Earth and Planetary Science Letters|volume=180|pages=13–27|doi=10.1016/S0012-821X(00)00159-X}}</ref><ref name="Duncan">{{cite journal|title=Rapid eruption of the Deccan flood basalts at the Cretaceous/Tertiary boundary|author=Duncan, RA & Pyle, DG|date=1988|journal=Nature|volume=333|pages=841–843|doi=10.1038/333841a0}}</ref>

The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulphuric aerosols into the air which might have blocked sunlight and thereby reducing photosynthesis in plants. In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions which would have increased the [[greenhouse effect]] when the dust and aerosols cleared from the atmosphere.<ref name="Duncan"/> Before the mass extinction of the dinosaurs, the release of [[volcanic gas]]ses during the formation of the [[Deccan traps]] "contributed to an apparently massive [[Global warming#History|global warming]]. Some data point to an average rise in temperature of 8 °C (14 °F) in the last half million years before the [[Chicxulub Crater|impact [at Chicxulub]]]."<ref>{{cite journal|author=Hofman, C, Féraud, G & Courtillot, V|date=2000|title=40Ar/39Ar dating of mineral separates and whole rocks from the Western Ghats lava pile: further constraints on duration and age of the Deccan traps|journal=Earth and Planetary Science Letters|volume=180|pages=13–27|doi=10.1016/S0012-821X(00)00159-X}}</ref><ref name="Duncan"/>

In the years when the Deccan Traps theory was linked to a slower extinction, [[Luis Alvarez]] (who died in 1988) replied that [[paleontologists]] were being misled by [[Signor-Lipps effect|sparse data]]. While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in [[sea level]] and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions.<ref>{{cite book|author=Alvarez, W|title=T. rex and the Crater of Doom|date=1997|publisher=Princeton University Press|isbn=978-0691016306|pages=130–146}}</ref>

===Possible Paleocene survivors===
Nonavian dinosaur remains are occasionally found above the K-T boundary. In 2002, paleontologists Zielinski and Budahn reported the discovery of a single [[hadrosauridae|hadrosaur]] leg bone fossil in the San Juan Basin, New Mexico and described it as evidence of [[Paleocene dinosaurs]]. The formation in which the bone was discovered has been dated to the early [[Paleocene]] epoch approximately 64.5 million years ago. If the bone was not re-deposited into that [[stratum]] by weathering action, it would provide evidence that some dinosaur populations may have survived at least a half million years into the Cenozoic Era.<ref name="Fassett">{{cite journal|url=http://www.lpi.usra.edu/meetings/impact2000/pdf/3139.pdf|title=Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico and Colorado, USA|author=Fassett, JE, Lucas, SG, Zielinski, RA, and Budahn, JR|date=2001|journal=Catastrophic events and mass extinctions, Lunar and Planetary Contribution|volume=1053|pages=45-46|accessdate=2007-05-18}}</ref> Other evidence includes the finding of dinosaur remains in the [[Hell Creek Formation]] up to 1.3&nbsp;meters (51&nbsp;in) above (40,000&nbsp;yearslater than) the K-T boundary. Similar reports have come from other parts of the world, including China.<ref name="Sloan">{{cite journal|author=Sloan, R. E., Rigby, K,. Van Valen, L. M., Gabriel, Diane|date=1986|title=Gradual dinosaur extinction and simultaneous ungulate radiation in the Hell Creek formation|journal=Science|volume=232|issue=4750|pages=629-633|url=http://www.sciencemag.org/cgi/content/abstract/232/4750/629|doi=10.1126/science.232.4750.629.|accessdate=2007-05-18}}</ref> Many scientists, however, dismiss the "Paleocene dinosaurs" as re-worked, i.e. washed out of their original locations and then re-buried in much later sediments,<ref name=FS05>{{cite journal |last=Fastovsky |first=David E. |coauthors=and Sheehan, Peter M. |year=2005 |title=Reply to comment on "The Extinction of the dinosaurs in North America" |journal=GSA Today |volume=15 |pages=11 |url=http://www.gsajournals.org/archive/1052-5173/15/7/pdf/i1052-5173-15-7-11a.pdf |format=pdf }}</ref><ref>{{cite journal|last=Sullivan|first=RM|title=No Paleocene dinosaurs in the San Juan Basin, New Mexico|url=http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm|journal=Geological Society of America Abstracts with Programs|volume=35|issue=5|pages=15|date=2003|accessdate=2007-07-02}}</ref> or find that, if correct, the presence of a handful of dinosaurs in the early Paleocene would not change the underlying facts of the extinction.<ref name=FS05/>

==History of discovery==
Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese, whose modern word for dinosaur is ''konglong'' (恐龍, or "terrible dragon"), considered them to be [[Chinese dragon|dragon]] [[bone]]s and documented them as such. For example, ''Hua Yang Guo Zhi'', a book written by Zhang Qu during the [[Western Jin Dynasty]], reported the discovery of dragon bones at Wucheng in [[Sichuan]] Province.<ref>{{cite book|author=[[Dong Zhiming]]|year=1992|title=Dinosaurian Faunas of China|publisher=China Ocean Press, Beijing|id=ISBN 3-540-52084-8}}</ref> Villagers in central China have been digging up dinosaur bones for decades, thinking they were from dragons, to make traditional medicine.<ref>{{cite web| last =| first =| authorlink =| coauthors =| title =Dinosaur bones 'used as medicine' | work =| publisher =BBC News| date =2007| url =http://news.bbc.co.uk/2/hi/asia-pacific/6276948.stm| format =| doi =| accessdate =2007-07-06}}</ref> In Europe, dinosaur fossils were generally believed to be the remains of [[Giant (mythology)|giants]] and other creatures killed by the [[Deluge (mythology)|Great Flood]].

[[Image:Buckland detail.png|thumb|left|130px|[[William Buckland]].]]
''[[Megalosaurus]]'' was the first dinosaur to be formally described, in 1677, when part of a bone was recovered from a [[limestone]] [[quarry]] at Cornwell near [[Chipping Norton, Oxfordshire|Chipping Norton]], [[Oxfordshire]], [[England]]. This bone fragment was identified correctly as the lower extremity of the [[femur]] of an animal larger than anything living in modern times. The second dinosaur genus to be identified, ''[[Iguanodon]]'', was discovered in 1822 by the English geologist [[Gideon Mantell]], who recognized similarities between his fossils and the bones of modern [[iguana]]s. Two years later, the Rev [[William Buckland]], a professor of [[geology]] at [[University of Oxford|Oxford University]], unearthed more fossilized bones of ''Megalosaurus'' and became the first person to describe dinosaurs in a [[scientific journal]].<ref name=WAS97>{{cite book |last=Sarjeant |first=William A.S. |editor=Farlow, James O.; and Brett-Surman, Michael K. (eds.) |title=The Complete Dinosaur |year=1997 |publisher=Indiana University Press |location=Bloomington |isbn=0-253-33349-0 |pages=3-11 |chapter=The earliest discoveries }}</ref>

The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1842 the English paleontologist [[Richard Owen]] coined the term "dinosaur". He recognized that the remains that had been found so far, ''Iguanodon'', ''Megalosaurus'' and ''[[Hylaeosaurus]]'', shared a number of distinctive features, and so decided to present them as a distinct taxonomic group. With the backing of [[Prince Albert of Saxe-Coburg-Gotha]], the husband of [[Victoria of the United Kingdom|Queen Victoria]], Owen established the [[Natural History Museum]] in [[South Kensington]], [[London]], to display the national collection of dinosaur fossils and other biological and geological exhibits.

In 1858, the first known American dinosaur was discovered, 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]] foulkii''. It was an extremely important find; ''Hadrosaurus'' was the first nearly complete dinosaur skeleton found 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 dinosaur mania in the [[United States]].

[[Image:OthnielCharlesMarsh.jpg|left|thumb|130px|[[Othniel Charles Marsh]], 19th century photograph.]]
[[Image:edcope.jpg|130px|right|thumb|[[Edward Drinker Cope]], 19th century photograph.]]

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]]. The feud probably originated when Marsh publicly pointed out that Cope's reconstruction of an ''[[Elasmosaurus]]'' skeleton was flawed; Cope had inadvertently placed the [[plesiosaur]]'s head at what should have been the animal's tail end. The 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. Marsh 'won' the contest primarily because he was better funded through a relationship with the [[US Geological Survey]]. Unfortunately, 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 (a method modern paleontologists would find appalling). 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, for a total of 142 new species. Cope's collection is now at the [[American Museum of Natural History]] in [[New York]], while Marsh's is on display at the [[Peabody Museum of Natural History]] at [[Yale University]].<ref>{{cite book|author=Holmes T|title=Fossil Feud: The Bone Wars of Cope and Marsh, Pioneers in Dinosaur Science|date=1996|publisher=Silver Burdett Press|isbn=978-0382391477}}</ref>

Since 1897, the search for dinosaur fossils has extended to every continent, including [[Antarctica]]. The first Antarctic dinosaur to be discovered, the [[ankylosaur]]id ''[[Antarctopelta|Antarctopelta oliveroi]]'', was found on [[Ross Island]] in 1986, although it was 1994 before an Antarctic species, the theropod ''[[Cryolophosaurus ellioti]]'', was formally named and described in a scientific journal.

Current dinosaur "hot spots" include southern South America (especially [[Argentina]]) and [[China]]. China in particular has produced many exceptional [[feathered dinosaur]] specimens due to the unique geology of its dinosaur beds, as well as an ancient arid climate particularly conducive to [[fossil]]ization.

===The "dinosaur renaissance"===
{{main|Dinosaur renaissance}}
The field of dinosaur research has enjoyed a surge in activity that began in the 1970s and is ongoing. This was triggered, in part, by [[John Ostrom]]'s discovery of ''[[Deinonychus]]'', an active predator that may have been [[warm-blooded]], in marked contrast to the then-prevailing image of dinosaurs as sluggish and [[cold-blooded]]. [[Vertebrate paleontology]], arguably the primary scientific discipline involved in dinosaur research, has become a global [[science]]. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including [[India]], South America, [[Madagascar]], [[Antarctica]], and most significantly in [[China]] (the amazingly well-preserved [[feathered dinosaurs]] in [[China]] have further consolidated the link between dinosaurs and their conjectured living descendants, modern birds). The widespread application of [[cladistics]], which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in [[scientific classification|classifying]] dinosaurs. Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary [[fossil record]].

==Cultural depictions==
{{main|Cultural depictions of dinosaurs}}
[[Image:London - Crystal Palace - Victorian Dinosaurs 1.jpg|right|thumb|170px|A ''[[Megalosaurus]]'' stalks [[Crystal Palace Park]] in [[London]].]]
By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the public imagination and become an enduring part of human culture. Only three decades after the first scientific descriptions of dinosaur remains, the famous [[Crystal Palace dinosaurs|dinosaur sculptures]] were erected in [[Crystal Palace Park]] in [[London]]. These sculptures excited the public so strongly that smaller replicas were sold, one of the first examples of [[tie-in]] [[merchandising]]. Since Crystal Palace, dinosaur exhibitions have opened at parks and [[Museum#Natural history museums|museums]] around the world, both catering to, and reinforcing, the public interest.<ref name="torrens1993">{{cite journal|author=Torrens, H.S.|date=1993|title=The dinosaurs and dinomania over 150 years|journal=Modern Geology|volume=18|issue=2|pages=257-286}}</ref> Dinosaur popularity has long had a reciprocal effect on dinosaur science, as well. The competition between museums for public attention led directly to the [[Bone Wars]] waged between Marsh and Cope, each striving to return with more spectacular fossil remains than the other, and the resulting contribution to dinosaur science was enormous.<ref name="breithaupt1997">{{cite book|author=Breithaupt, Brent H.|date=1997|title=First golden period in the USA." In: Currie, Philip J. & Padian, Kevin (Eds.). ''The Encyclopedia of Dinosaurs''|publisher=University of California Press|pages=347-350|isbn=978-0122268106}}</ref>

Dinosaurs hold an integral place in modern culture. The word "dinosaur" itself has entered the English [[lexicon]] as an expression describing anything that is impractically large, slow-moving, or obsolete, bound for extinction.<ref name="m-w">"[http://www.m-w.com/dictionary/dinosaur Definition of dinosaur]" Merriam-Webster's Online Dictionary. Accessed [[26 May]] [[2007]].</ref> The public preoccupation with dinosaurs led to their inevitable entrance into worldwide [[popular culture]]. Beginning with a passing mention of ''Megalosaurus'' in the first paragraph of [[Charles Dickens]]' ''[[Bleak House]]'' in 1852,<ref name="bleakhouse">"''London. Michaelmas term lately over, and the Lord Chancellor sitting in Lincoln's Inn Hall. Implacable November weather. As much mud in the streets, as if the waters had but newly retired from the face of the earth, and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborne Hill.''" From page 1 of Dickens, Charles J.H. (1852). ''Bleak House''. London: Bradbury & Evans.</ref> dinosaurs have been featured in a broad array of [[fiction]]al works. [[Sir Arthur Conan Doyle]]'s 1912 book ''[[The Lost World (Arthur Conan Doyle)|The Lost World]]'', the iconic 1933 [[motion picture|film]] ''[[King Kong (1933 film)|King Kong]]'', the 1954 introduction of ''[[Godzilla (1954 film)|Godzilla]]'' and its many subsequent sequels, the best-selling 1990 novel ''[[Jurassic Park]]'' by [[Michael Crichton]] and its 1993 [[Jurassic Park (film)|film version]], briefly the [[List of highest-grossing films|highest-grossing film of all time]], are just a few prominent examples of the long tradition of dinosaurs in fiction. [[Non-fiction]] authors, including some prominent paleontologists, have also sought to take advantage of dinosaur popularity, especially among children, to educate readers about dinosaurs in particular and science in general. Dinosaurs are ubiquitous in [[advertising]], with numerous [[Company (law)|companies]] seeking to utilize dinosaurs to sell their own products or to characterize their rivals as slow-moving or obsolete.<ref name=DFGlut1997>{{cite book|author=Glut, DF, & Brett-Surman, MK|date=1997|title=Dinosaurs and the media." In: Farlow, James O. & Brett-Surman, Michael K. (Eds.). ''The Complete Dinosaur''|publisher=Indiana University Press|pages=675-697|isbn=978-0253213136}}</ref>

==Religious views==
{{main|Young Earth Creationism#Palaeontology and dinosaurs}}
Various religious groups have views about dinosaurs that differ from those held by the vast majority of scientists, usually due to conflicts with [[Creationism|creation stories]] in their scriptures. However, most of the [[Scientific method|scientific]] community rejects these religiously-inspired interpretations of dinosaurs.<ref name="Kitcher">{{cite book| last =Kitcher| first =Philip| authorlink =| coauthors =| title = Abusing Science: The Case Against Creationism| publisher =MIT Press| date =1983| location =| pages = 213| url =http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=5383| doi =| isbn = 978-0-262-61037-7 }}</ref><ref name="Dawkins">{{cite book| last =Dawkins| first =Richard| authorlink =| coauthors =| title = The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe Without Design| publisher =W.W. Norton| date =1996| location =| pages =400| url =| doi =| isbn =978-0393315707}}</ref>

==See also==
{{portalpar|Dinosaurs}}
* [[Dinosaur classification]]
* [[Fossil]]s
* [[List of dinosaurs]]
* [[List of fossil sites]] ''(with link directory)''
* [[Prehistoric life]]
* [[Prehistoric reptile]]s

==Notes and references==
{{reflist|2}}

==General references==
<div class="references-small">
* Kevin Padian, and Philip J. Currie. (1997). ''Encyclopedia of Dinosaurs''. Academic Press. ISBN 0-12-226810-5. (Articles are written by experts in the field).
* [[Gregory S. Paul|Paul, Gregory S.]] (2000). ''The Scientific American Book of Dinosaurs''. St. Martin's Press. ISBN 0-312-26226-4.
*Paul, Gregory S. (2002). ''Dinosaurs of the Air: The Evolution and Loss of flight in Dinosaurs and Birds''. Baltimore: The Johns Hopkins University Press. ISBN 0-8018-6763-0.
*[[David B. Weishampel|Weishampel, David B.]] (2004). ''The Dinosauria''. University of California Press; 2nd edition. ISBN 0-520-24209-2.
</div>

==See also==
{{seealsosection
|commons=Dinosauria
|portal=Dinosaurs}}

==External links==
<!--Sorted (roughly) from least to most technical-->
{{Spoken Wikipedia|Dinosaur.ogg|2005-12-30}}
<!-- link to the recorded version: http://en.wikipedia.org/w/index.php?title=Dinosaur&oldid=33253062 -- It should be inserted into the template, as an actual link, because it's rather laborious to roll back among thousands of changes and find a specific revision in the history.-->

;For children
*[http://www.enchantedlearning.com/subjects/dinosaurs/ Zoom Dinosaurs] (''www.enchantedlearning.com'') From Enchanted Learning. Kid's site, info pages, theories, history.

;Images
*[http://dino.lm.com/images/ The Art Gallery] of The Dinosauricon, hosting over 2000 images from many different artists working in different styles.
<!--*[http://www.paleograveyard.com/ The Grave Yard], featuring skeletal restorations of a variety of prehistoric animals.-->
*[http://skeletaldrawing.com/ Skeletal Drawing] Professional restorations of numerous dinosaurs, and discussions of dinosaur anatomy.

;Popular
*[http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/index.html Dinosaurs & other extinct creatures]: From the [[Natural History Museum]], a well illustrated dinosaur directory.
<!--*[http://www.dinosaur.org/ Dinosaur Interplanetary Gazette] (''www.dinosaur.org'') The first online dinosaur magazine.(cited in ''The Dinosauria'')-->
*[http://www.dinosaurnews.org/ Dinosaurnews] (''www.dinosaurnews.org'') The dinosaur-related headlines from around the world. Recent news on dinosaurs, including finds and discoveries, and many links.
*[http://www.ucmp.berkeley.edu/diapsids/dinosaur.html Dinosauria] From UC Berkeley Museum of Paleontology Detailed information - scroll down for menu.
*[http://www.livescience.com/dinosaurs/ LiveScience.com] All about dinosaurs, with current featured articles.
*[http://www.dinoruss.com/ Dino Russ's Lair] hosts a large collection of dinosaur-related links.

;Technical
*[http://palaeo-electronica.org/ ''Palaeontologia Electronica''] From Coquina Press. Online technical journal.
*[http://dinobase.gly.bris.ac.uk Dinobase] A searchable dinosaur database, from the University of Bristol, with dinosaur lists, classification, pictures, and more.
*[http://www.dinodata.org/index.php DinoData] (''www.dinodata.org'') Technical site, essays, classification, anatomy.
*[http://www.dinosauria.com/dml/dml.htm Dinosauria On-Line] (''www.dinosauria.com'') Technical site, essays, pronunciation, dictionary.
*[http://dino.lm.com/ The Dinosauricon] By T. Michael Keesey. Technical site, cladogram, illustrations and animations.
*[http://www.users.qwest.net/~jstweet1/ Thescelosaurus!] By Justin Tweet. Includes a cladogram and small essays on each relevant genera and species.
*[http://www.palaeos.com/Vertebrates/Units/Unit310/000.html Dinosauromorpha Cladogram] From [http://www.Palaeos.com Palaeos]. A detailed amateur site about all things paleo.
*[http://www.dinoruss.com/de_4/dino30.htm The Dinosaur Encyclopaedia], an extensive overview of genera-based dinosaur information from 1999 and before.

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[[Category:Paleontology]]
[[Category:Paleozoology]]

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[[da:Dinosaurus]]
[[de:Dinosaurier]]
[[el:Δεινόσαυρος]]
[[es:Dinosauria]]
[[eo:Dinosaŭro]]
[[eu:Dinosauro]]
[[fa:دایناسور]]
[[fr:Dinosaure]]
[[gl:Dinosauro]]
[[ko:공룡]]
[[hi:डायनोसोर]]
[[hr:Dinosauri]]
[[id:Dinosaurus]]
[[is:Risaeðla]]
[[it:Dinosauri]]
[[he:דינוזאורים]]
[[jv:Dinosaurus]]
[[ka:დინოზავრები]]
[[sw:Dinosau]]
[[ku:Dînosaur]]
[[la:Dinosauria]]
[[lv:Dinozauri]]
[[lt:Dinozaurai]]
[[li:Dinosaurusse]]
[[hu:Dinoszaurusz]]
[[ml:ഡൈനസോര്‍]]
[[ms:Dinosaur]]
[[nl:Dinosauriërs]]
[[ja:恐竜]]
[[no:Dinosaurer]]
[[nn:Dinosaurus]]
[[oc:Dinosaures]]
[[pa:ਡਾਯਨੋਸੋਰ]]
[[pl:Dinozaury]]
[[pt:Dinossauros]]
[[ro:Dinozaur]]
[[qu:Dinusawru]]
[[ru:Динозавры]]
[[scn:Dinusauru]]
[[simple:Dinosaur]]
[[sk:Dinosaury]]
[[sl:Dinozavri]]
[[sr:Диносауруси]]
[[su:Dinosaurus]]
[[fi:Dinosaurukset]]
[[sv:Dinosaurier]]
[[ta:தொன்மா]]
[[th:ไดโนเสาร์]]
[[vi:Khủng long]]
[[tr:Dinozor]]
[[uk:Динозаври]]
[[ur:حیوان المہیب]]
[[yi:דיינעסאר]]
[[bat-smg:Dinuozaurā]]
[[zh:恐龙]]

Revision as of 19:38, 27 February 2008

Yes I know

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