Editing Dinosaur (section)

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

{{multiple image
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|image1 = Saurischia pelvis.png
|alt1 = 
|caption1 = [[Saurischia]]n pelvis structure (left side)

|image2 = Tyrannosaurus pelvis left.jpg
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|caption2 = ''[[Tyrannosaurus]]'' pelvis (showing saurischian structure&nbsp;– left side)

|image3 = Ornithischia pelvis.png
|alt3 = 
|caption3 = [[Ornithischia]]n pelvis structure (left side)

|image4 = Edmontosaurus pelvis left.jpg
|alt4 = 
|caption4 = ''[[Edmontosaurus]]'' pelvis (showing ornithischian structure&nbsp;– left side)
}}

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

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

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

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

===Taxonomy===
[[File:Ornithopods jconway.jpg|thumb|Restoration of six [[Ornithopoda|ornithopod]]s; far left: ''[[Camptosaurus]]'', left: ''[[Iguanodon]]'', center background: ''[[Shantungosaurus]]'', center foreground: ''[[Dryosaurus]]'', right: ''[[Corythosaurus]]'', far right (large) ''[[Tenontosaurus]]''.]]
[[File:Ceratopsidae-BW-003.png|thumb|Restoration of four [[Ceratopsidae|ceratopsids]]: top left – ''[[Triceratops]]'', top right – ''[[Styracosaurus]]'', bottom left – ''[[Anchiceratops]]'', bottom right – ''[[Chasmosaurus]]''.]]
[[File:Macronaria scrubbed enh.jpg|thumb|Restoration of four [[macronaria]]n [[Sauropoda|sauropods]]: from left to right ''[[Camarasaurus]]'', ''[[Brachiosaurus]]'', ''[[Giraffatitan]]'', and ''[[Euhelopus]]'']]
[[File:Dromaeosaurs.png|thumb|[[paleoart|Restoration]] of six [[Dromaeosauridae|dromaeosaurid]] [[Theropoda|theropods]]: from left to right ''[[Microraptor]]'', ''[[Velociraptor]]'', ''[[Austroraptor]]'', ''[[Dromaeosaurus]]'', ''[[Utahraptor]]'', and ''[[Deinonychus]]'']]

The following is a simplified classification of dinosaur groups based on their evolutionary relationships, and those of the main dinosaur groups Theropoda, Sauropodomorpha and Ornithischia, compiled by Justin Tweet.<ref>{{Cite web|author=Justin Tweet|url=https://equatorialminnesota.blogspot.com/p/blog-page_20.html|title=Classification diagrams|website=Equatorial Minnesota|access-date=2022-09-06|archive-date=November 4, 2022|archive-url=https://web.archive.org/web/20221104195358/https://equatorialminnesota.blogspot.com/p/blog-page_20.html|url-status=live}}</ref> Further details and other hypotheses of classification may be found on individual articles.

*Dinosauria
**†[[Ornithischia]] ("bird-hipped"; diverse bipedal and quadrupedal herbivores)
***†[[Saphornithischia]] ("true" ornithischians)
****†[[Heterodontosauridae]] (small herbivores/omnivores with prominent [[canine tooth|canine-like teeth]])
*****†[[Genasauria]] ("cheeked lizards")
******†[[Thyreophora]] (armored dinosaurs; bipeds and quadrupeds)
*******†[[Eurypoda]] (heavy, quadrupedal thyreophorans)
********†[[Stegosauria]] (spikes and plates as primary armor)
*********†[[Huayangosauridae]] (small stegosaurs with flank osteoderms and tail clubs)
*********†[[Stegosauridae]] (large stegosaurs)
********†[[Ankylosauria]] ([[scute]]s as primary armor)
*********†[[Parankylosauria]] (small, southern ankylosaurs with [[macuahuitl]]-like tails)
*********†[[Nodosauridae]] (mostly spiky, club-less ankylosaurs)
*********†[[Ankylosauridae]] (characterized by flat scutes)
**********†[[Ankylosaurinae]] (club-tailed ankylosaurids)
******†[[Neornithischia]] ("new ornithischians")
*******†[[Pyrodontia]] ("fire teeth")
********†[[Thescelosauridae]] ("wondrous lizards")
*********†[[Orodrominae]] (burrowers)
*********†[[Thescelosaurinae]] (large thescelosaurids)
********†[[Cerapoda]] ("horned feet")
*********†[[Marginocephalia]] (characterized by a cranial growth)
**********†[[Pachycephalosauria]] (bipeds with domed or knobby growth on skulls)
**********†[[Ceratopsia]] (bipeds and quadrupeds; many had neck frills and horns)
***********†[[Chaoyangsauridae]] (small, frill-less basal ceratopsians)
***********†[[Neoceratopsia]] ("new ceratopsians")
************†[[Leptoceratopsidae]] (little to no frills, hornless, with robust jaws)
************†[[Protoceratopsidae]] (basal ceratopsians with small frills and stubby horns)
*************†[[Ceratopsoidea]] (large-horned ceratopsians)
**************†[[Ceratopsidae]] (large, elaborately ornamented ceratopsians)
***************†[[Chasmosaurinae]] (ceratopsids with enlarged brow horns)
***************†[[Centrosaurinae]] (ceratopsids mostly characterized by frill and nasal ornamentation)
****************†[[Nasutoceratopsini]] (centrosaurines with enlarged nasal cavities)
****************†[[Centrosaurini]] (centrosaurines with enlarged nasal horns)
****************†[[Pachyrhinosaurini]] (mostly had nasal bosses instead of horns)
*********†[[Ornithopoda]] (various sizes; bipeds and quadrupeds; evolved a method of chewing using skull flexibility and numerous teeth)
**********†[[Hypsilophodontidae]] (small European neornithischians)
**********†[[Iguanodontia]] ("iguana teeth"; advanced ornithopods)
***********†[[Rhabdodontomorpha]] (with distinctive dentition)
************†[[Tenontosauridae]] (North American rhabdodontomorphs; bipeds and quadrupeds)
************†[[Rhabdodontidae]] (European rhabdodontomorphs)
***********†[[Euiguanodontia]] ("true iguanodonts")
************†[[Elasmaria]] (mostly southern ornithopods with mineralized plates along the ribs; may be thescelosaurids)
************†[[Dryomorpha]] (''[[Dryosaurus]]'' and more advanced ornithopods)
*************†[[Dryosauridae]] (mid-sized, small headed)
**************†[[Ankylopollexia]] (early members mid-sized, stocky)
***************†[[Styracosterna]] ("spiked [[Sternum|sterna]]")
****************†[[Hadrosauriformes]] (ancestrally had a thumb spike; large quadrupedal herbivores, with teeth merged into dental batteries)
*****************†[[Hadrosauromorpha]] (hadrosaurids and their closest relatives)
******************†[[Hadrosauridae]] ("duck-billed dinosaurs"; often with crests)
*******************†[[Saurolophinae]] (hadrosaurids with solid, small, no crests)
********************†[[Brachylophosaurini]] (short-crested)
********************†[[Kritosaurini]] (enlarged, solid nasal crests)
********************†[[Saurolophini]] (small, spike-like crests)
********************†[[Edmontosaurini]] (flat-headed saurolophines)
*******************†[[Lambeosaurinae]] (hadrosaurids often with hollow crests)
********************†[[Aralosaurini]] (solid-crested)
********************†[[Tsintaosaurini]] (vertical, tube-like crests)
********************†[[Parasaurolophini]] (long, backwards-arcing crests)
********************†[[Lambeosaurini]] (usually rounded crests)
**[[Saurischia]]
***†[[Herrerasauridae]] (early bipedal carnivores)
***†[[Sauropodomorpha]] (herbivores with small heads, long necks, and long tails)
****†[[Unaysauridae]] (primitive, strictly bipedal "prosauropods")
****†[[Plateosauria]] (diverse; bipeds and quadrupeds)
*****†[[Massopoda]] ("heavy feet")
******†[[Massospondylidae]] (long-necked, primitive sauropodomorphs)
******†[[Riojasauridae]] (large, primitive sauropodomorphs)
*******†[[Sauropodiformes]] (heavy, bipeds and quadrupeds)
********†[[Sauropoda]] (very large and heavy; quadrupedal)
*********†[[Lessemsauridae]] (gigantic yet lacking several weight-saving adaptations)
*********†[[Gravisauria]] ("heavy lizards")
**********†[[Eusauropoda]] ("true sauropods")
***********†[[Turiasauria]] (often large, widespread sauropods)
***********†[[Neosauropoda]] ("new sauropods"; columnar limbs)
************†[[Diplodocoidea]] (skulls and tails elongated; teeth typically narrow and pencil-like)
*************†[[Rebbachisauridae]] (short-necked, low-browsing diplodocoids often with high backs)
*************†[[Flagellicaudata]] (whip-tailed)
**************†[[Dicraeosauridae]] (small, short-necked diplodocoids with enlarged cervical and dorsal vertebrae)
**************†[[Diplodocidae]] (extremely long-necked)
***************†[[Apatosaurinae]] (robust cervical vertebrae)
***************†[[Diplodocinae]] (long, thin necks)
************†[[Macronaria]] (boxy skulls; spoon- or pencil-shaped teeth)
*************†[[Titanosauriformes]] ("titan lizard forms")
**************†[[Brachiosauridae]] (long-necked, long-armed macronarians)
**************†[[Somphospondyli]] ("porous vertebrae")
***************†[[Euhelopodidae]] (stocky, mostly Asian)
***************†[[Diamantinasauria]] (horse-like skulls; restricted to the Southern Hemisphere; may be titanosaurs)
***************†[[Titanosauria]] (diverse; stocky, with wide hips; most common in the Late Cretaceous of southern continents)
***[[Theropoda]] (carnivorous)
****[[Neotheropoda]] ("new theropods")
*****†[[Coelophysoidea]] (early theropods; includes ''[[Coelophysis]]'' and close relatives)
*****†"Dilophosaur-grade neotheropods" (larger kink-snouted dinosaurs)
*****[[Averostra]] ("bird snouts")
******†[[Ceratosauria]] (generally elaborately horned carnivores that existed from the Jurassic to Cretaceous periods, originally included Coelophysoidea)
*******†[[Ceratosauridae]] (ceratosaurs with large teeth) 
*******†[[Abelisauroidea]] (ceratosaurs exemplified by reduced arms and hands)
********†[[Abelisauridae]] (large abelisauroids with short arms and oftentimes elaborate facial ornamentation)
********†[[Noasauridae]] (diverse, generally light theropods; may include several obscure taxa)
*********†[[Elaphrosaurinae]] (bird-like; omnivorous as juveniles but herbivorous as adults)
*********†[[Noasaurinae]] (small carnivores)
******[[Tetanurae]] (stiff-tailed dinosaurs)
*******†[[Megalosauroidea]] (early group of large carnivores)
********†[[Piatnitzkysauridae]] (small basal megalosauroids endemic to the Americas)
********†[[Megalosauridae]] (large megalosauroids with powerful arms and hands)
********†[[Spinosauridae]] (crocodile-like, semiaquatic carnivores)
*******[[Avetheropoda]] ("bird theropods")
********†[[Carnosauria]] (large meat-eating dinosaurs; megalosauroids sometimes included)
*********†[[Metriacanthosauridae]] (primitive Asian allosauroids)
*********†[[Allosauridae]] (''[[Allosaurus]]'' and its very closest relatives)
*********†[[Carcharodontosauridae]] (robust allosauroids; includes some of the largest purely terrestrial carnivores)
********[[Coelurosauria]] (feathered theropods, with a range of body sizes and niches)
*********†[[Megaraptora]]? (theropods with large hand claws; potentially tyrannosauroids or neovenatorids)
*********†"Nexus of basal coelurosaurs" (used by Tweet to denote well-known taxa with unstable positions at the base of Coelurosauria)
*********[[Tyrannoraptora]] ("tyrant thieves")
**********†[[Tyrannosauroidea]] (mostly large, primitive coelurosaurs)
***********†[[Proceratosauridae]] (tyrannosauroids with head crests)
***********†[[Tyrannosauridae]] (''[[Tyrannosaurus]]'' and close relatives)
**********[[Maniraptoriformes]] (bird-like dinosaurs)
***********†[[Ornithomimosauria]] (small-headed, mostly toothless, omnivorous or possible herbivores)
************†[[Ornithomimidae]] (very ostrich-like dinosaurs)
***********[[Maniraptora]] (dinosaurs with pennaceous feathers)
************†[[Alvarezsauroidea]] (small hunters with reduced forelimbs)
*************†[[Alvarezsauridae]] (insectivores with only one enlarged digit)
************†[[Therizinosauria]] (tall, long-necked theropods; omnivores and herbivores)
*************†[[Therizinosauroidea]] (larger therizinosaurs)
**************†[[Therizinosauridae]] (sloth-like herbivores, often with enlarged claws)
************†[[Oviraptorosauria]] (omnivorous, beaked dinosaurs)
*************†[[Caudipteridae]] (bird-like, basal oviraptorosaurs)
*************†[[Caenagnathoidea]] (cassowary-like oviraptorosaurs)
**************†[[Caenagnathidae]] (toothless oviraptorosaurs known from North America and Asia)
**************†[[Oviraptoridae]] (characterized by two bony projections at the back of the mouth; exclusive to Asia)
************[[Paraves]] (avialans and their closest relatives)
*************†[[Scansoriopterygidae]] (small tree-climbing theropods with membranous wings)
*************†[[Deinonychosauria]] (toe-clawed dinosaurs; may not form a natural group)
**************†[[Archaeopterygidae]] (small, winged theropods or primitive birds)
**************†[[Troodontidae]] (omnivores; enlarged brain cavities)
**************†[[Dromaeosauridae]] ("raptors")
***************†[[Microraptoria]] (characterized by large wings on both the arms and legs; may have been capable of powered flight)
***************†[[Eudromaeosauria]] (hunters with greatly enlarged sickle claws)
**************†[[Unenlagiidae]] (piscivores; may be dromaeosaurids)
***************†[[Halszkaraptorinae]] (duck-like; potentially semiaquatic)
***************†[[Unenlagiinae]] (long-snouted)
*************[[Avialae]] (modern birds and extinct relatives)

===Timeline of major groups===

Timeline of major dinosaur groups per {{harvcoltxt|Holtz|2007}}.

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 bar:era
 from: -251   till:  -199.6    color:triassic  text:[[Triassic]]         
 from: -199.6    till: -145.5    color:jurassic    text:[[Jurassic]]
 from: -145.5    till: -65.5   color:cretaceous    text:[[Cretaceous]]
 from: -65.5   till:  -23.03    color:paleogene  text:[[Paleogene]]         
 from: -23.03    till: -2.588    color:neogene    text:[[Neogene]]
 from: -2.588    till: 0   color:quaternary    text:[[Quaternary|Q.]]

</timeline>