''Coelophysis'' ( traditionally; or , as heard more commonly in recent decades) is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

coelophysid Coelophysoidea is an extinct clade of theropod dinosaurs common during the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivore, carnivorous fo ...

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

that lived approximately 215 to 201.4

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

during the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

period from the middle

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

age in what is now the southwestern United States. ''

Megapnosaurus ''Megapnosaurus'' (meaning "big dead lizard", from Greek μέγα = "big", ἄπνοος = "not breathing", "dead", σαῦρος = "lizard") is an extinct genus of coelophysid theropod dinosaur that lived approximately 188 million years ago du ...

'' was once considered to be a species within this genus, but this interpretation has been challenged and the genus ''Megapnosaurus'' is now considered valid. ''Coelophysis'' was a small, slenderly built, ground-dwelling,

bipedal Bipedalism is a form of terrestrial locomotion where an animal moves by means of its two rear (or lower) limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' ...

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they ar ...

that could grow up to long. It is one of the earliest known dinosaur genera. Scattered material representing similar animals has been found worldwide in some

and

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

formations. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''C. bauri'', originally given to the genus '' Coelurus'' by

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...

in 1887, was described by the latter in 1889. The names ''Longosaurus'' and ''Rioarribasaurus'' are synonymous with ''Coelophysis''. ''Coelophysis'' is one of the most specimen-rich dinosaur genera.

History of discovery

In April of

1887 Events January * January 11 – Louis Pasteur's anti-rabies treatment is defended in the Académie Nationale de Médecine, by Dr. Joseph Grancher. * January 20 ** The United States Senate allows the United States Navy to lease Pearl Har ...

American paleontologist

first described vertebrate remains from the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

as new species of the genus '' Coelurus'', including nearly all parts of the skeleton except the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

and

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

. While ''Coelurus'' had been considered by its describer

Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of paleontology. A prolific fossil collector, Marsh was one of the preeminent paleontologists of the nineteenth century. Among his legacies are the discovery or ...

as an uncertain type of reptile, the new material described by Cope demonstrated that it was a

, and likely closely related to '' Megadactylus'' from the Triassic of

Massachusetts Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...

. Cope chose to name two new species from his collection of New Mexican material, the first being ''Coelurus longicollis'' for multiple and a , while the second was ''Coelurus bauri'', named after German paleontologist Georg Baur, included the same regions of the skeleton. Following this description, Cope reclassified his New Mexican material in July 1887 from ''Coelurus'' to the German taxon '' Tanystrophaeus'' based on the similarities of the vertebrae, creating the new combinations ''Tanystrophaeus longicollis'' and ''Tanysteophaeus bauri''. Cope described additional material of both ''T. longicollis'' and ''T. bauri'' to cover more of the anatomy of both species, and he also named the new species ''Tanystrophaeus willistoni'' for a partial

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

even smaller than both other species, named after American paleontologist

Samuel Wendell Williston Samuel Wendell Williston (July 10, 1852 – August 30, 1918) was an American educator, entomologist, and Paleontology, paleontologist who was the first to propose that birds developed flight Origin of birds#Origin of bird flight, cursorially (by ...

. Following this, Cope came to the realization that the vertebrae of ''Tanystrophaeus'' he considered similar to the New Mexican species were not definitively caudal vertebrae, and as a result the species were in need of a new genus name. As a result, in

1889 Events January * January 1 ** The total solar eclipse of January 1, 1889 is seen over parts of California and Nevada. ** Paiute spiritual leader Wovoka experiences a vision, leading to the start of the Ghost Dance movement in the Dakotas ...

Cope named ''Coelophysis'' for ''C. longicollis'', ''C. bauri'', and ''C. willistoni'', with the name as a combination of the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

words κοῖλος (''koilos''), "hollow", and φύσεις (''fysis''), "form". The original material of ''Coelophysis'' described by Cope was all collected by David Baldwin in 1881 from three localities of

Rio Arriba County, New Mexico Rio Arriba County () is a List of counties in New Mexico, county in the U.S. state of New Mexico. As of the 2020 United States census, 2020 census, the population was 40,363. Its county seat is Tierra Amarilla, New Mexico, Tierra Amarilla. Its ...

, with the only surviving collection information being labels written by Baldwin associated with the specimens, indicating a provenance of below a

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

layer at "Arroyo Seco" and "Gallina Canyon". The layer of gypsum identified by Baldwin is now known as part of the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

Todilto Formation that overlies the Chinle Formation within the region of Ghost Ranch that "Arroyo Seco" (Arroyo Canjilon or Canjilon Creek) flows past, so while no other information on the area Baldwin collected can be known for certain, he must have collected from within a region around Ghost Ranch where the river cuts through the Chinle Formation below the Todilto gypsum layer. Williston and

Ermine Cowles Case Ermine Cowles Case (September 11, 1871CASE, Emine Cowles
in ''

German paleontologist Friedrich von Huene revisited the material and taxonomy of ''Coelophysis'' in a 1906

review A review is an evaluation of a publication, product, service, or company or a critical take on current affairs in literature, politics or culture. In addition to a critical evaluation, the review's author may assign the work a content rating, ...

of Triassic dinosaurs, following the species identifications of Cope and illustrating the material for the first time, with the additional description of elements of the hand of ''C. longicollis'' and vertebrae of ''C. bauri'' that Cope had not described. Huene did not see justification in considering ''Coelophysis'' a close relative of '' Anchisaurus'' (a replacement name for ''Megadactylus''), instead classifying the genus within Coeluridae. In a further 1915 review limited to the New Mexican collection of Cope, Huene separated the specimens into the three species differently from previously, assigning bones based on size with ''C. longicollis'' as the largest species and ''C. willistoni'' as the smallest and suggesting that more than three species may be present. No

for ''Coelophysis'' was designated by Huene, nor were specimen numbers identified, complicating the assignment of material to the species. In 1986 American paleontologist Kevin Padian revisited the type material of ''Coelophysis'' and identified which material was referred to which species by Cope and Huene in their studies, and identified some material in the Cope collection that had yet to be described.

Ghost Ranch discoveries

During the summer of 1946, American paleontologist Edwin H. Colbert began searching for Triassic fossils in the Petrified Forest National Park of northern

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, under the employment of the

American Museum of Natural History The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...

. This exploration continued the following year, where Colbert planned to stop at Ghost Ranch on the way to Petrified Forest, where many skulls of phytosaurs had been found. Colbert, along with George Simpson, Bill Fish, George Whitaker, and Tom Ierardi, were the field crew for the 1947 season, with Simpson and Fish focusing on

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

mammals of northern New Mexico while Colbert, Whitaker, and Ierardi would continue to northern Arizona for Triassic reptiles. On 21 June, Colbert, Whitaker and Ierardi began exploring the sediments of the Chinle Formation in the area near Ghost Ranch, uncovering a complete phytosaur skull, and on 22 June Whitaker discovered some fragments including a claw that Colbert identified as ''Coelophysis'', from a

talus slope Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. The term ''scree'' is ap ...

above an intermittent

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...

. Upon excavating bones on the surface and removing some of the talus, a fossil layer was found containing numerous ''Coelophysis'' bones. After several more days of excavations, it was understood that the fossil layer contained hundreds of skeletons of ''Coelophysis'' in a single concentration, and upon the return of Simpson and Fish to the locality the former stated that "this was the greatest find ever made in the Triassic of North America". Ghost Ranch Coelophysis Quarry

Excavations of the Ghost Ranch ''Coelophysis'' quarry were continued throughout 1947 and 1948 by the crew of the AMNH, which also included Carl Sorensen after arrival from

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

, assisted by the landowners Arthur and Phoebe Pack and farm hand Herman Hall. Seven large blocks were excavated, each containing numerous skeletons, numbered I to VI for identification of location when transported back to the AMNH. Around 105 smaller blocks were also collected, created by the channels excavated to separate the larger blocks. A further 6 blocks, VII to XIII, were excavated as the quarry expanded to several meters in diameter, with the blocks being distributed amongst the AMNH,

Museum of Northern Arizona The Museum of Northern Arizona is a museum in Flagstaff, Arizona, United States, established as a repository for Indigenous material and natural history specimens from the Colorado Plateau. The museum was founded in 1928 by zoologist Dr. Harol ...

, New Mexico Museum of Natural History, and Yale Peabody Museum. All of the excavations at Ghost Ranch took place within the upper

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

level of the Chinle Formation, believed to be

in age at the time and making the expanse of ''Coelophysis'' one of the longest deposits within the Chinle despite being one of the earliest known dinosaurs. Colbert believed that the original material of ''Coelophysis'' may have been collected from the surface in a similar method to Whitaker's discovery, as part of the same fossil layer that was excavated by the AMNH. Upon completion of the AMNH excavations at Ghost Ranch at the end of 1948 the quarry was abandoned, with the hillside above slumping down to cover the dig site, and the land itself gifted to the

Presbyterian Church Presbyterianism is a historically Reformed Christianity, Reformed Protestantism, Protestant tradition named for its form of ecclesiastical polity, church government by representative assemblies of Presbyterian polity#Elder, elders, known as ...

. After 32 years in this state, American paleontologist David Berman of the

Carnegie Museum of Natural History The Carnegie Museum of Natural History (abbreviated as CMNH) is a natural history museum in the Oakland (Pittsburgh), Oakland neighborhood of Pittsburgh, Pennsylvania. It was founded by List of people from the Pittsburgh metropolitan area, Pit ...

approached Reverend Jim Hall of Ghost Ranch to propose reopening of the dinosaur quarry with the intention of collecting a specimen for display in the museum. Hall agreed to reopen the quarry on the condition that Colbert and the recently opened New Mexico Museum of Natural History would both participate, with the MNA, YPM and

University of Toronto The University of Toronto (UToronto or U of T) is a public university, public research university whose main campus is located on the grounds that surround Queen's Park (Toronto), Queen's Park in Toronto, Ontario, Canada. It was founded by ...

additionally contributing to the efforts. The quarry was worked from 1981 to 1982, with 16 large blocks of excavated, and all but one block being removed. The last block remained at the site until 1985 when it was moved by American paleontologist David Gillette to the new Ruth Hall Museum of Paleontology at Ghost Ranch. Blocks from both collections were distributed by the primary institutions through trades and sale to be distributed across all of North America, and eventually even other continents. Coelophysis bauri

monograph A monograph is generally a long-form work on one (usually scholarly) subject, or one aspect of a subject, typically created by a single author or artist (or, sometimes, by two or more authors). Traditionally it is in written form and published a ...

on ''Coelophysis'' was then published by Colbert in 1989, focusing primarily on the material collected by him at the AMNH but supplemented by material in various other institutions. Under the belief that the material of Baldwin was found near at the same locality as the dinosaur quarry, Colbert diagnosed ''Coelophysis'' using the anatomy of the complete skeletons he had excavated, and considered ''C. bauri'' the

senior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

of ''C. longicollis'' and ''C. willistoni'', with the partial sacrum AMNH 2722 as the

lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...

of the species. ''C. longicollis'' had been believed by American paleontologist Samuel P. Welles to be a different genus than ''Coelophysis'', which he had named ''Longosaurus'' in 1984 after American paleontologist Robert A. Long. All of the Ghost Ranch material was thus described as part of a single species known from hundreds of individuals of various ages and sizes, with some additional variation in proportions of individuals at the same size that gave the suggestion of a "robust" and "gracile" morph. While Colbert considered ''Coelophysis'' to be diagnostic, this opinion was not shared in other reviews of early theropods, where Padian instead considered it a "metataxon" or otherwise lacking unique characteristics of its own and having anatomy primitive to

Theropoda Theropoda (; from ancient Greek iktionary:θηρίον, , (''therion'') "wild beast"; wiktionary:πούς, , wiktionary:ποδός, (''pous, podos'') "foot" is one of the three major groups (Clade, clades) of Dinosaur, dinosaurs, alon ...

. Padian believed that as ''Coelophysis'' was founded in scrappy and incomplete material, it is difficult to justify the referrals of additional material to the taxon. He still considered ''Coelophysis'' a useful taxonomic entity, being characterized by the lack of more derived traits common to other theropods, and as a result a partial skeleton from Petrified Forest, and the theropods '' Avipes'', ''Podokesaurus'', ''Procompsognathus'', and '' Trialestes'' could be considered referrable to ''Coelophysis''. Hayden Quarry

American paleontologists Adrian P. Hunt and Spencer G. Lucas went further than Padian, declaring ''Coelophysis'' a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

'' as its type material could not be distinguished from other theropods. As a result, they determined that a new taxon was required for the very complete specimens from Ghost Ranch (what they referred to as the Whitaker Quarry), for which they named ''Rioarribasaurus colberti''. The genus name referred to the Rio Arriba County where the fossils were discovered, while the species name was in honor of Colbert for his work excavating and describing the material. Hunt and Lucas also designated a lectotype for ''C. longicollis'' as the specimen chosen by Welles as its type was invalid, identifying that the cervical AMNH 2701 should be used to identify the species. A lectotype was also designated for ''C. willistoni'', the partial ilium AMNH 2726. None of the material of the three species was believed by Hunt and Lucas to bear any unique characteristics that could support their synonymy to ''C. bauri'' or any other theropod. The complete skeleton AMNH 7224, mounted on display at the museum, was selected as the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

of ''Rioarribasaurus'', and all the Ghost Ranch specimens collected from 1947 to 1982 were referred to the taxon as they lacked differences beyond sexual or growth-related variation. In a following study in 1996, Hunt and Lucas as well as American paleontologists Robert M. Sullivan and Andrew Heckert established that the locality where Baldwin collected ''Coelophysis'' was not the same deposit or level as the dinosaur quarry as Colbert had believed. The color and concretions attached to the bones Baldwin collected differs from those of the specimens named ''Rioarribasaurus'', but was instead identical to material found at a separate cluster of sites along Arroyo Seco below the Todilto Formation. The Baldwin localities would therefore be from the region of Orphan Mesa southeast of the dinosaur quarry, and from older deposits equivalent to the Canjilon Quarry and aetosaur quarry where '' Pseudopalatus'' and '' Typothorax'' are known. According to the stratigraphy of Sullivan, Lucas and colleagues, ''Coelophysis'' would therefore be from the Revueltian-age Petrified Forest Formation, with ''Rioarribasaurus'' from the

Apachean The Apache ( ) are several Southern Athabaskan language-speaking peoples of the Southwest, the Southern Plains and Northern Mexico. They are linguistically related to the Navajo. They migrated from the Athabascan homelands in the north into th ...

-age Rock Point Formation. Additional collected material from these relocated sites was used as justification for ''Coelophysis'' being a distinct taxon separated from ''Rioarribasaurus'', showing differences in the pubis, femur, and metatarsals. The stratigraphic divisions of Lucas for the Chinle are not supported by other paleontologists, who instead place the ''Coelophysis'' quarry within a "siltstone member" of the Chinle Formation with a

age, with the Baldwin sites as part of the Petrified Forest Member radiometrically dated to 211.9±0.7

in the late

. Since the numerous well-preserved Ghost Ranch specimens were used as ''Coelophysis'' in most of the scientific literature as well as public mentions, the introduction of ''Rioarribasaurus'' would have caused much confusion. As such, Colbert and other paleontologists petitioned to the

International Commission on Zoological Nomenclature The International Commission on Zoological Nomenclature (ICZN) is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 26 commissioners from 20 countries. Orga ...

to replace the lectotype of ''Coelophysis bauri'' with AMNH 7224 as a

neotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...

, thereby making ''Coelophysis bauri'' and ''Rioarribasaurus colberti'' objective synonyms, giving ''Coelophysis'' a much better type specimen, and preserving the use of ''Coelophysis'' for the Ghost Ranch material as it had been since its discovery in 1947. They emphasised their belief that the Ghost Ranch quarry was from approximately the same level and place as the original collection, as well as that the lectotype sacrum of ''C. bauri'' belonged to the same taxon as AMNH 7224 as justification for the neotype. The petition was met with opposing comments by Hunt, Lucas, and Sullivan, as well as Welles, George Olshevsky, and Philip Huber, on the grounds of stratigraphic and possibly anatomical differences between the original material and more complete specimens, and that the synonymy of ''Rioarribasaurus'' and ''Coelophysis'' should be established though anatomy rather than by ruling, while it was supported by paleontologists including

Hans-Dieter Sues Hans-Dieter Sues (born 1956) is a German-born American palaeontologist who is a Senior Research Geologist and Curator of Vertebrate Paleontology at the National Museum of Natural History of the Smithsonian Institution in Washington, DC. Career ...

, Thomas R. Holtz Jr., Farish Jenkins, Ralph Molnar, Elizabeth Nicholls, Louis L. Jacobs, who presented views of the common use of ''Coelophysis'', the potential that the stratigraphic and anatomical differences suggested were invalid, and the belief that a replacement of the type by a better specimen helps with the continued use of taxa over time even when originally diagnostic material is later shown to be inadequate. American

paleoartist Paleoart (also spelled palaeoart, paleo-art, or paleo art) is any original artistic work that attempts to depict prehistoric life according to scientific evidence.#Anson, Ansón, Fernández & Ramos (2015) pp. 28–34. Works of paleoart may be r ...

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...

also published in 1993 the opinion that ''Coelophysis'' was indeterminate, but that ''Rioarribasaurus'' and '' Syntarsus'' belonged to the same genus, creating the combination ''Syntarsus colberti''. In the end, the ICZN voted in 1996 to designate the complete specimen AMNH 7224 as the neotype ''Coelophysis'' and dispose of the name ''Rioarribasaurus'', declaring the latter a ''nomen rejectum'', or "rejected name", thus resolving the confusion and uncertainty surrounding the status of ''Coelophysis''. The name ''Coelophysis'' became a ''nomen conservandum'' ("conserved name").

Formerly assigned material and taxa

In 1922 Case described the first supposed material of ''Coelophysis'' from outside New Mexico with the referral of a series of vertebrae he collected in 1921 from Dockum Formation of

Crosby County, Texas Crosby County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 5,133. The county seat is Crosbyton. The county was founded in 1876 and later organized in 1886. Both the county and its seat are named fo ...

. The specimen, UMMP No. 7507, was considered by Case as an indeterminate species of ''Coelophysis'', with similarities in the elongation to both ''Coelophysis'' and ''Anchisaurus''. Huene did not agree with the referral by case, naming the new coelurosaur genus '' Spinosuchus'' for the material. The greatest difference from ''Coelophysis'' was in the elongate neural spines, but he also referred a partial braincase from the same region that shows differences from the only other comparable braincase, that of '' Thecodontosaurus''. Redescription of ''Spinosuchus'' in 2009 showed that it was separate from ''Coelophysis'' and not even a theropod, being a member of the early archosauriform group

Trilophosauridae Trilophosaurs are lizard-like Triassic allokotosaur reptiles related to the archosaurs. The best known genus is '' Trilophosaurus'', a herbivore up to long. It had a short, unusually heavily built skull, equipped with massive, broad flattened ...

. Following the rediscovery of a specimen containing the bone impressions of an early dinosaur by Colbert and Donald Baird in 1958, ''Coelophysis'' was first compared to ''Podokesaurus'' as potentially synonymous. BSNH No. 13656 was found in the in 1864 from possibly-Triassic sediments of

Connecticut Connecticut ( ) is a U.S. state, state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the south. ...

, probably the Portland Formation, and remained undescribed until the work of Colbert and Baird. ''Podokesaurus'' had been named in 1911 by American paleontologist Mignon Talbot for a partial skeleton from the Portland Formation with the only species ''P. holyokensis'', the same deposits which bore the BSNH specimen. Comparisons between the BSNH specimen, ''Podokesaurus'', and ''Coelophysis'' showed that they all differed minimally in the limb material in common, with Colbert and Baird assigning BSNH 13656 to an indeterminate ''Coelophysis'' species and suggesting that ''Podokesaurus'' may not be valid. This was followed up by Colbert in 1964 where he proposed that ''Podokesaurus'' should be considered a

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

of ''Coelophysis'' and created the new combination ''C. holyokensis'', to which he also referred the BSNH specimen. Colbert no longer followed this synonymy by his 1989 monograph on ''Coelophysis'', finding that the shared similarities were widespread throughout podokesaurids, and though some later authors considered ''Podokesaurus'' a synonym most now consider it indeterminate or potentially undiagnostic. In 1983 another partial skeleton of a theropod was found from the Orphan Mesa region where it is possible Baldwin collected the original ''Coelophysis'' material, at a site named Cross Quarry after its discoverer Robert Cross. The specimen, NMMNH P-22298 and known informally as the "Orphan Mesa theropod", was an incomplete skeleton of an immature theropod, preserving several , the , parts of the and most of the hindlimb. Following the designation of AMNH 7224 as the neotype of ''Coelophysis bauri'', ''C. longicollis'', ''C. willistoni'', and the specimens named ''C. bauri'' by Cope lacked a genus and species, so the NMMNH P-22298 as well as material previously assigned to ''C. willistoni'' (AMNH 2706) were named '' Eucoelophysis'' by Sullivan and Lucas in 1999. When originally named, Sullivan and Lucas placed ''Eucoelophysis'' within Ceratosauria as a close relative of ''Coelophysis'', '' Syntarsus rhodesiensis'', and '' Syntarsus kayentakatae''. American paleontologists Andrew Heckert and colleagues in 2000 referred further theropod material to ''Eucoelophysis'' (as ''E.'' sp.) from the Snyder Quarry elsewhere in the Chinle Formation, suggesting it may belong to a new species, which they reiterated in 2003. These referrals and the identify of ''Eucoelophysis'' was reevaluated in 2006 by Argentine paleontologist Martín Ezcurra who identified that many of the features used by Sullivan and Lucas to support the identity of ''Eucoelophysis'' were instead shared amongst all early dinosaurs, with ''Eucoelophysis'' instead appearing more similar to the non-dinosaur '' Silesaurus''. Neither the Snyder Quarry specimens nor the material originally assigned to ''C. longicollis'' were found to share features with ''Eucoelophysis'' by Ezcurra, who identified them instead as indeterminate coelophysoids. An articulated skeleton ( TMP 1986.63.33) from the ''Coelophysis'' quarry previously considered a specimen of ''Coelophysis'' was moved to ''Eucoelophysis'' by American paleontologist Larry Rinehart and colleagues in 2009, but it was returned to ''Coelophysis'' in 2018 by American paleontologist Chris Griffin. The identification of ''Eucoelophysis'' as a silesaurid, distant from ''Coelophysis'' and the Baldwin material, was upheld by independent work by American paleontologists Sterling Nesbitt, Randall Irmis and William Parker in 2007. Snout and front teeth of Coelophysis and Syntarsus

Snout and front teeth of Coelophysis and Syntarsus

While the

Zimbabwe file:Zimbabwe, relief map.jpg, upright=1.22, Zimbabwe, relief map Zimbabwe, officially the Republic of Zimbabwe, is a landlocked country in Southeast Africa, between the Zambezi and Limpopo Rivers, bordered by South Africa to the south, Bots ...

an genus '' Syntarsus'' was first described by South African paleontologist Michael A. Raath as a separate genus of podokesaurid, it was compared very favourably to ''Coelophysis'' by both Raath and Colbert, with differences in bone fusion and the pelvis separating the two taxa. The similarity between the two genera was extended upon by American paleontologist

in 1984, who considered ''Syntarsus'' a species of ''Coelophysis'', ''C. rhodesiensis'', as well as finding ''Halticosaurus'' to be a probable synonym. ''Syntarsus'' and ''Coelophysis'' were distinguished by Padian in 1986 despite his referral of many other Triassic theropods lacking unique features to ''Coelophysis'', but Paul maintained the synonymy of the two genera in 1988 and 1993, including assigning ''Rioarribasaurus colberti'' to ''Syntarsus'' as ''S. colberti'' under the belief that ''Coelophysis'' was undiagnostic but the Ghost Ranch specimens were not. American paleontologist Timothy B. Rowe kept ''Syntarsus'' and ''Coelophysis'' separate in his 1989 description of the new species '' Syntarsus kayentakatae'', but in 2000 American paleontologist Alex Downs reiterated the opinion of synonymy between ''Coelophysis'' and ''Syntarsus'', crediting the poor description of some features of ''Coelophysis'' by Colbert to previous misinterpretations. Downs also found that the theropod '' Camposaurus'' could not be distinguished from ''Coelophysis'', and considered it undiagnostic, but it was reidentified as a distinct coelophysid by Ezcurra and American paleontologist Stephen Brusatte in 2011. Further complications with ''Syntarsus'' occurred when it was recognized that the genus name had been preoccupied by a colydiine beetle named in 1869, which prompted American and Polish entomologists Michael Ivie, Adam Ślipiński, and Piotr Węgrzynowicz to provide the new replacement name ''

'' for the theropod in 2001, with ''M. rhodesiensis'' becoming its type. Many paleontologists did not like the naming of ''Megapnosaurus'', partially because taxonomists are generally expected to allow original authors of a name to correct any mistakes in their work. Raath was aware of the homonymy between the dinosaur ''Syntarsus'' and beetle ''Syntarsus'', but the group who published ''Megapnosaurus'' have claimed that they believed Raath was deceased and unable to correct his mistake, so they proceeded accordingly. American paleontologist Mickey Mortimer pointed out that "Paleontologists might have reacted more positively if the replacement name (''Megapnosaurus'') hadn't been facetious, translating to "big dead lizard". In 2024, it has been petitioned to the ICZN that ''Syntarsus'' be retained for the name of the theropod. In the interim, Bristowe and Raath (2004) first proposed the synonymy of both species of ''Syntarsus'' with ''Coelophysis'', though they were uncertain whether ''S. kayentakatae'' belonged to this genus, referring it to as ?''C. kayentatakatae''. Multiple authors in the 2000s provisionally considered ''S. rhodesiensis'' to be a species of ''Coelophysis'', while ''S. kayentakatae'' has been identified as belonging to a separate genus and in need of a new name.

Phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analyses of Coelophysidae have found that ''S. rhodesiensis'' is not the sister taxon to ''Coelophysis'', so the name ''Megapnosaurus'' has been used in those cases.

Description

''Coelophysis'' is known from a number of complete fossil skeletons of the species ''C. bauri''. This lightly built dinosaur measured up to long and was more than a meter tall at the hips.

(1988) estimated the weight of the gracile form at and the weight of the robust form at , but later presented a higher estimate of . ''Coelophysis'' was a bipedal, carnivorous, theropod dinosaur and a fast, agile runner. Despite its basal position within

, the bauplan of ''Coelophysis'' differed from those of other basal theropods, such as '' Herrerasaurus'', showing more derived traits common in theropods that superseded it. The torso of ''Coelophysis'' conforms to the basic theropod bauplan, but the

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...

displays some special characteristics. ''C. bauri'' had a furcula (wishbone), the earliest known example in a dinosaur. ''Coelophysis'' also preserves the ancestral condition of possessing four digits on the hand (manus). It had only three functional digits, with the fourth being embedded in the flesh of the hand. ''Coelophysis'' had narrow hips, arms adapted for grasping prey, and narrow feet. Its neck and tail were long and slender. The

and hindlimbs of ''C. bauri'' are also slight variations on the theropod body plan. It has the open

acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...

and straight ankle hinge that define Dinosauria. The leg ended in a three-toed foot ( pes) with a raised dewclaw (

hallux Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plantigrade''; ...

). The tail had an unusual structure within its interlocking prezygapophysis of its vertebrae, which formed a semi-rigid lattice, apparently to stop the tail from moving up and down. Coelophysis neotype skull

''Coelophysis'' had a long and narrow head (approximately ), with large, forward-facing eyes that afforded it

stereoscopic Stereoscopy, also called stereoscopics or stereo imaging, is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...

vision and, as a result, excellent depth perception. Rinehart ''et al.'' (2004) described the complete

sclerotic ring The scleral ring or sclerotic ring is a hardened ring of plates, often derived from bone, that is found in the eyes of many animals in several groups of vertebrates. Some species of mammals, amphibians, and crocodilians lack scleral rings. The rin ...

found for a juvenile ''Coelophysis bauri'' (specimen NMMNH P-4200) and compared it to data on the sclerotic rings of reptiles (including birds), concluding that ''Coelophysis'' was a diurnal, visually oriented predator. The study found that the vision of ''Coelophysis'' was superior to most lizards' vision and ranked with that of modern birds of prey. The eyes of ''Coelophysis'' appear to be the closest to those of eagles and hawks, with a high power of accommodation. The data also suggested poor night vision, which would mean this dinosaur had a round pupil rather than a split pupil. ''Coelophysis'' had an elongated snout with large fenestrae that helped to reduce skull weight, while narrow struts of bones preserved the structural integrity of the skull. The neck had a pronounced

sigmoid Sigmoid means resembling the lower-case Greek letter sigma (uppercase Σ, lowercase σ, lowercase in word-final position ς) or the Latin letter S. Specific uses include: * Sigmoid function, a mathematical function * Sigmoid colon, part of the l ...

curve. The braincase is known in ''Coelophysis bauri'', but little data could be derived because the skull was crushed. Unlike some other theropods, the cranial ornamentation of ''Coelophysis'' was not located at the top of its skull. Low, laterally raised bony ridges were present on the dorsolateral margin of the nasal and lacrimal bones in the skull, directly above the

antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...

Distinguishing anatomical features

A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group. According to Ezcurra (2007) and Bristowe and Raath (2004), ''Coelophysis'' can be distinguished based on the absence of an offset rostral process of the maxilla, the quadrate being strongly caudally, a small external mandibular fenestra (which is 9–10% of the mandibular length), and the anteroposterior length of the ventral lacrimal process is greater than 30% of its height. Several paleontologists consider ''Coelophysis bauri'' to be the same dinosaur as ''Megapnosaurus rhodesiensis'' (formerly ''Syntarsus''). However, this has been refuted by many paleontologists. Downs (2000) concluded that ''C. bauri'' differs from ''C. rhodesiensis'' in cervical length, proximal and distal leg proportions, and proximal caudal vertebral anatomy. Tykoski and Rowe (2004) concluded that ''C. bauri'' differs from ''M. rhodesiensis'' in that it lacks a pit at the base of the nasal process of the premaxilla. Bristowe and Raath (2004) concluded that ''C. bauri'' differs from ''M. rhodesiensis'' in having a longer maxillary tooth row. Barta ''et al''. (2018) concluded that ''C. bauri'' differed from ''M. rhodesiensis'' in that it bears its 5th metacarpal. Griffin (2018) concluded that ''C. bauri'' differs from ''M. rhodesiensis'' in several differences in the musculature of the limbs.

Classification

When first described, Cope believed that ''Coelophysis'' was a member of the carnivorous dinosaur group Goniopoda, as a relative of ''Anchisaurus'', ''Coelurus'' and at times ''Tanystropheus''. Huene, in his 1906 reevaluation of Triassic dinosaurs, found that ''Coelophysis'' differed significantly from the families Plateosauridae and Thecodontosauridae (which included ''Anchisaurus''), and that ''Tanystropheus'' was an intermediate early reptile and not a dinosaur. Huene believed that ''Coelophysis'' represented the earliest, and first Triassic, member of the

family Coeluridae, as a relative of the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

taxa ''Coelurus'', ''

Compsognathus ''Compsognathus'' (; Ancient Greek, Greek ''kompsos''/κομψός; "elegant", "refined" or "dainty", and ''gnathos''/γνάθος; "jaw") is a genus of small, bipedalism, bipedal, carnivore, carnivorous theropoda, theropod dinosaur. Members o ...

'', and '' Ornitholestes'' and also later

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

members. Huene maintained a similar classification later in 1914 and then 1915, but had changed his opinion on the status of Dinosauria following the suggestion of British paleontologist Harry Govier Seeley that was not a natural group, with

Saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithi ...

and

Ornithischia Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...

replacing it. From this, Huene created the new subgroups of Saurischia, Pachypodosauria for large carnivores and

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

s, and Coelurosauria for slender carnivores. Triassic coelurosaurs were separated into two families, the Hallopoda and the Podokesauridae, the latter of which included the Triassic genera ''Coelophysis'', '' Halticosaurus'', '' Podokesaurus'', ''

Procompsognathus ''Procompsognathus'' is an extinct genus of Coelophysidae, coelophysid Theropoda, theropod dinosaur that lived approximately 210 million years ago during the later part of the Triassic Period (geology), Period, in what is now Germany. ''Procomp ...

'', ''

Saltopus ''Saltopus'' ("hopping foot") is a genus of very small bipedal dinosauriform containing the single species ''Saltopus elginensis'' from the late Triassic period of Scotland. It is one of the most famous Elgin Reptiles. Description ''Saltopu ...

'' and '' Tanystropheus''. From podokesaurids, ''Podokesaurus'' was believed to give rise to the Jurassic and Cretaceous

Compsognathidae Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Period (geology), Periods. The bird-like features of these species, a ...

while ''Coelophysis'' was believed to give rise to Jurassic-only Coeluridae. The placement of ''Coelophysis'' as a coelurosaur continued to be followed by Huene and Hungarian paleontologist Franz Nopcsa, though its classification amongst coelurosaurs was variable. In 1921 Huene moved ''Coelophysis'' into the Coeluridae from the Podokesauridae alongside ''Halticosaurus'', while he would retain it within Podokesauridae later in 1932 and 1956. Other podokesaurids were also reclassified during this time into the families Procompsognathidae or Halticosauridae of Huene, or the subfamilies Coelophysinae and Podokesaurinae named by Nopcsa, with ''Coelophysis'' by 1956 only considered a close relative of ''Podokesaurus'', ''Saltopus'', '' Lukousaurus'' and '' Spinosuchus''. A taxonomic scheme based on the work of Huene was followed by American paleontologists including Alfred Sherwood Romer and Colbert with modifications. Romer found in 1956 that Podokesauridae included ''Coelophysis'' and almost all Triassic coelurosaurs, and Colbert in 1964 believed that ''Coelophysis'' was the best-known podokesaurid, both differing from Huene by treating Coelurosauria as an early branch of Theropoda and not recognizing Pachypodosauria. The family Coelophysidae was first recognized by American paleontologist Samuel P. Welles in 1984 who described ''

Dilophosaurus ''Dilophosaurus'' ( ) is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 186 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserv ...

'' and reviewed early theropods. Welles advocated for abandoning Coelurosauria as a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group that gave rise to later theropods, and instead recognized many families of Triassic and Jurassic theropods of uncertain interrelationships. ''Coelophysis bauri'' was placed along with '' Sarcosaurus'' as coelophysids, while ''C. longicollis'' (as ''Longosaurus'') was placed as a halticosaurid alongside ''Dilophosaurus'', ''Halticosaurus'' and '' Liliensternus''. The family Procompsognathidae was also recognized to include Triassic genera, while ''Podokesaurus'' was unable to be classified due to its incompleteness and Podokesauridae was abandoned. Colbert did not follow this during his 1989 description of the Ghost Ranch specimens, recognising ''Coelophysis'', ''Halticosaurus'', ''Podokesaurus'', ''Procompsognathus'' and '' Syntarsus'' as podokesaurids, but American paleontologist Thomas R. Holtz Jr. in 1994 followed Welles, using Coelophysidae for ''Coelophysis'' and its relatives, considering ''Podokesaurus'' indeterminate, and naming the new clade Coelophysoidea to unite coelophysids with ''

''.

''Coelophysis'' is a distinct taxonomic unit (genus), composed of the single species ''C. bauri.'' Two additional originally described species, ''C. longicollis'' and ''C. willistoni'', are now considered dubious and undiagnostic. ''M. rhodesiensis'' was referred to ''Coelophysis'' for several years, but it is likely its own genus and is known from the early Jurassic of southern Africa. A third possible species is ''Coelophysis kayentakatae'', previously referred to the genus ''Megapnosaurus,'' from the

Kayenta Formation The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau area of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Originally suggested as being Sinemur ...

of the southwestern US. In recent phylogenetic analyses, ''"Syntarsus" kayentakatae'' has been shown to be distantly related to ''Coelophysis'' and ''Megapnosaurus'', suggesting that it belongs to its own genus.

Paleobiology

Feeding

Coelophysis with crocodylomorph bones AMNH

The teeth of ''Coelophysis'' were typical of predatory dinosaurs, as they were blade-like, recurved, sharp, jagged, and finely serrated on both the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

and posterior edges. Its dentition shows that it was carnivorous, probably preying on the small, lizard-like animals that were discovered with it. It may also have hunted in packs to tackle larger prey. ''Coelophysis bauri'' has approximately 26 teeth on the maxillary bone of the upper jaw and 27 teeth on the dentary bone of the lower jaw. Kenneth Carpenter (2002) examined the bio-mechanics of theropod arms and attempted to evaluate their usefulness in predation. He concluded that the arm of ''Coelophysis'' was flexible and had a good range of motion, but its bone structure suggested that it was comparatively weak. The "weak" arms and small teeth in this genus suggested that ''Coelophysis'' preyed upon animals that were substantially smaller than itself. Rinehart ''et al.'' agreed that ''Coelophysis'' was a "hunter of small, fast-moving prey". Carpenter also identified three distinct models of theropod arm use and noted that ''Coelophysis'' was a "combination grasper-clutcher", as compared to other dinosaurs that were "clutchers" or "long armed graspers". It has been suggested that ''C. bauri'' was a

cannibal Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecology, ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is also well ...

, based on supposed juvenile specimens found "within" the abdominal cavities of some Ghost Ranch specimens. However, Robert J. Gay showed in 2002 that these specimens were misinterpreted. Several specimens of "juvenile coelophysids" were actually small crurotarsan reptiles, such as '' Hesperosuchus''. Gay's position was lent support in a 2006 study by Nesbitt ''et al.'' In 2009, new evidence of cannibalism came to light when additional preparation of previously excavated matrix revealed regurgitate material in and around the mouth of ''Coelophysis'' specimen NMMNH P-44551. This material included tooth and jaw bone fragments that Rinehart ''et al.'' considered "morphologically identical" to a juvenile ''Coelophysis.'' In 2010, Gay examined the bones of juveniles found within the thoracic cavity of AMNH 7224 and calculated that the total volume of these bones was 17 times greater than the maximum estimated stomach volume of the ''Coelophysis'' specimen. Gay observed that the total volume would be even greater when considering that there would have been flesh on these bones. This analysis also noted the absence of tooth marks on the bones as would be expected in defleshing and the absence of expected pitting by stomach acids. Finally, Gay demonstrated that the alleged cannibalized juvenile bones were deposited stratigraphically below the larger animal that had supposedly cannibalized them. Taken together, these data suggested that the ''Coelophysis'' specimen AMNH 7224 was not a cannibal and that the bones of the juvenile and adult specimens were found in their final position as a result of "coincidental superposition of different sized individuals.

Pack behavior

The discovery of over 1,000 specimens of ''Coelophysis'' at the Whitaker quarry at Ghost Ranch has suggested gregarious behavior to researchers like Schwartz and Gillette. There is a tendency to see this massive congregation of animals as evidence for huge packs of ''Coelophysis'' roaming the land. No direct evidence for flocking exists because the deposits only indicate that large numbers of ''Coelophysis'', along with various other Triassic animals, were buried together. Some of the evidence from the

taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek language, Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientis ...

of the site indicates that these animals may have been gathered together to feed or drink from a depleted water hole or to feed on a

spawning Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is ...

run of fish, being later buried in a catastrophic

flash flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash f ...

or a drought. With 30 specimens of ''C. rhodesiensis'' found together in Zimbabwe, some palaeontologists have suggested that ''Coelophysis'' was indeed gregarious. Again, there is no direct evidence of flocking in this case and it has also been suggested that these individuals were also victims of flash flooding as it appears to have been commonplace during this period.G. Bond, 1965. Some new fossil localities in the Karroo System of Rhodesia. Arnoldia, Series of Miscellaneous Publications, National Museum of Southern Rhodesia 2(11):1–4M. A. Raath, 1977. The Anatomy of the Triassic Theropod Syntarsus rhodesiensis (Saurischia: Podokesauridae) and a Consideration of Its Biology. Department of Zoology and Entomology, Rhodes University, Salisbury, Rhodesia 1–233

Growth and sexual dimorphism

Rinehart (2009) assessed the ontogenic growth of this genus using data gathered from the length of its upper leg bone (

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

) and concluded that ''Coelophysis'' juveniles grew rapidly, especially during the first year of life. ''Coelophysis'' likely reached sexual maturity between the second and third year of life and reached its full size, just above 10 feet in length, by its eighth year. This study identified four distinct growth stages: 1-year, 2-year, 4-year, and 7+ year. It was also thought that, as soon as they were hatched, they would have to fend for themselves. Two "morphs" of ''Coelophysis'' have been identified. One is a more gracile form, as in specimen AMNH 7223, and the other is a slightly more robust form, as in specimens AMNH 7224 and NMMNH P-42200. Skeletal proportions were different between these two forms. The gracile form has a longer skull, a longer neck, shorter arms, and has sacral neural spines that are fused. The robust form has a shorter skull, a shorter neck, longer arms, and unfused sacral neural spines. Historically, many arguments have been made that this represents some sort of dimorphism in the population of ''Coelophysis'', probably

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

.Gay, R. (2005). "Sexual Dimorphism in the Early Jurassic Theropod Dinosaur ''

'' and a Comparison with Other Related Forms": In: Raath agreed that dimorphism in ''Coelophysis'' is evidenced by the size and structure of the arm. Rinehart ''et al.'' studied 15 individuals, and agreed that two morphs were present, even in juvenile specimens, and suggested that sexual dimorphism was present early in life, prior to sexual maturity. Rinehart concluded that the gracile form was female and the robust form was male based on differences in the sacral vertebrae of the gracile form, which allowed for greater flexibility for egg laying. Further support for this position was provided by an analysis showing that each morph comprised 50% of the population, as would be expected in a 50/50 sex ratio. However, more recent research has found that ''C. bauri'' and ''C. rhodesiensis'' had highly variable growth between individuals, with some specimens being larger in their immature phase than smaller adults were when completely mature. This indicates that the supposed presence of distinct morphs is simply the result of individual variation. This highly variable growth was likely ancestral to dinosaurs but later lost and may have given such early dinosaurs an evolutionary advantage in surviving harsh environmental challenges.

Reproduction

Through the compilation and analysis of a database of nearly three dozen reptiles (including birds) and comparison with existing data about the anatomy of ''Coelophysis'', Rinehart ''et al.'' (2009) drew the following conclusions. It was estimated that average egg of ''Coelophysis'' was 31–33.5 millimeters across its minor diameter and that each female would lay between 24 and 26 eggs in each clutch. The evidence suggested that some parental care was necessary to nurture the relatively small hatchlings during the first year of life, where they would reach 1.5 meters in length by the end of their first growth stage. ''Coelophysis bauri'' invested as much energy in reproduction as other extinct reptiles of its approximate size.

Paleopathology

In a 2001 study conducted by Bruce Rothschild and other paleontologists, 14-foot bones referred to ''Coelophysis'' were examined for signs of stress fracture, but none were found.Rothschild, B.; Tanke, D.H. & Ford, T.L. (2001). "Theropod stress fractures and tendon avulsions as a clue to activity": In: In ''C. rhodesiensis'', healed fractures of the

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

and metatarsus have been observed, but are very rare. " e supporting butresses of the second sacral rib" in one specimen of ''Syntarsus rhodesiensis'' showed signs of fluctuating asymmetry. Fluctuating

asymmetry Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...

results from developmental disturbances and is more common in populations under stress and can therefore be informative about the quality of conditions a dinosaur lived under.Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 337-363.

Ichnology

PSM V66 D145 Carnivorous dinosaur tracks in high relief preserved in stone

Edwin H. Colbert has suggested that the theropod footprints referred to the

ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxon'' comes from the Ancient Greek (''íchnos'') meaning "track" and English , itself derived from ...

'' Grallator'', located in the Connecticut River Valley across Connecticut and Massachusetts, may have been made by ''Coelophysis''. The footprints are from the Late Triassic to Early Jurassic aged Newark Supergroup. They clearly show digits II, III, and IV, but not I or V. That condition is strange for footprints of their age. The digits I and V were presumed to be stubby and ineffective, not touching the ground when the dinosaur was walking or running. They have been thought to be from an unidentified, primitive saurischian similar to ''Coelophysis'' by David B. Weishampel and L. Young more recently. Skeletal remains resembling ''Coelophysis'' have also been found in the valley, supporting the idea that a species similar to ''Coelophysis'' is responsible for the footprints.

Paleoenvironment

Specimens of ''Coelophysis'' have been recovered from the Chinle Formation of New Mexico and Arizona, more famously at the Ghost Ranch (Whitaker) quarry in the Rock Point member among other quarries in the underlying Petrified Forest member, the sediments of which have been dated to approximately 212 million years ago, making them part of the middle

stage of the Late Triassic, but Thomas Holtz Jr. interpreted that it was during the

stage from approximately 204 to 201.6 million years ago.Holtz, Thomas R. Jr. (2012) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2011 Appendix.
''C. rhodesiensis'' has been recovered in the Upper Elliott Formation in the

Cape A cape is a clothing accessory or a sleeveless outer garment of any length that hangs loosely and connects either at the neck or shoulders. They usually cover the back, shoulders, and arms. They come in a variety of styles and have been used th ...

and Free State provinces of South Africa, as well as the Chitake River bonebed quarry at the Forest Sandstone Formation in Zimbabwe. Ghost Ranch was located close to the equator over 200 million years ago, and had a warm, monsoon-like climate with heavy seasonal precipitation. Hayden Quarry, a new excavation site at Ghost Ranch, New Mexico, has yielded a diverse collection of fossil material that included the first evidence of dinosaurs and less-advanced dinosauromorphs from the same time period. The discovery indicates that the two groups lived together during the early Triassic period 235 million years ago. Therrien and Fastovsky (2001) examined the paleoenvironment of ''Coelophysis'' and other early theropods from Petrified Forest National Park in Arizona and determined that this genus lived in an environment that consisted of floodplains marked by distinct dry and wet seasons. There was a great deal of competition during drier times when animals struggled for water in riverbeds that were drying up. In the upper sections of the Chinle Formation where ''Coelophysis'' is found, dinosaurs were rare. So far, only ''

Chindesaurus ''Chindesaurus'' ( ) is an extinct genus of basal saurischian dinosaur from the Late Triassic (213-210 million years ago) of the southwestern United States. It is known from a single species, ''C. bryansmalli'', based on a partial skeleton recov ...

'' and ''

Daemonosaurus ''Daemonosaurus'' is an extinct genus of possible theropod dinosaur from the Late Triassic of New Mexico. The only known fossil is a skull and neck fragments from deposits of the latest Triassic Chinle Formation at Ghost Ranch. ''Daemonosaurus'' ...

'' are known, the terrestrial fauna being dominated instead by other reptiles like the rhynchocephalian '' Whitakersaurus'', the pseudosuchian '' Revueltosaurus'', the

aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...

s ''

Desmatosuchus ''Desmatosuchus'' (, from Greek language, Greek δεσμός ''desmos'' 'link' + σοῦχος ''soûkhos'' 'crocodile') is an extinct genus of archosaur belonging to the Order Aetosauria. It lived during the Late Triassic. Description ''Desma ...

'', '' Typothorax'' and '' Heliocanthus'', the crocodilomorph '' Hesperosuchus'', the "

rauisuchia "Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians ...

ns" '' Shuvosaurus'',Irmis, R.B. (2005). "The vertebrate fauna of the Upper Triassic Chinle Formation in northern Arizona": In: '' Effigia'', and '' Vivaron'', along with other rare components like the dinosauriform '' Eucoelophysis'' and the

amniote Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial animal, terrestrial and semiaquatic vertebrates. Amniotes evolution, evolved from amphibious Stem tet ...

'' Kraterokheirodon''. In the waterways there are the phytosaur ''

Machaeroprosopus ''Machaeroprosopus'' (from , 'large knife' and , 'bordering on') is an extinct genus of mystriosuchin leptosuchomorph phytosaur from the Late Triassic of the southwestern United States. ''M. validus'', once thought to be the type species of ''M ...

'', the archosauromorph ''

Vancleavea ''Vancleavea'' is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America. The type species, type and only known species is ''V. campi'', named by Robert Long & Phillip A Murry in 1995 in pa ...

'', the amphibians '' Apachesaurus'' and ''

Koskinonodon ''Anaschisma'' ("ripped up") is an extinct genus of large temnospondyls. These animals were part of the family called Metoposauridae, which filled the crocodile-like predatory Ecological niche, niches in the late Triassic. It had a large skull ab ...

'', and the fishes '' Reticulodus'', ''

Arganodus ''Arganodus'' is an extinct genus of freshwater lungfish that had a wide global distribution throughout much of the Triassic period, with a single species surviving across Gondwana into the Cretaceous. It is the only member of the family Argano ...

'', and '' Lasalichthyes''.

Taphonomy

The multitude of specimens deposited so closely together at Ghost Ranch was probably the result of a flash flood that swept away a large number of ''Coelophysis'' and buried them quickly and simultaneously. In fact, it seems that such flooding was commonplace during this period of the

Earth's history The natural history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by consta ...

and, indeed, the Petrified Forest of nearby

is the result of a preserved log jam of tree trunks that were caught in one such flood. Whitaker quarry at Ghost Ranch is considered a monotaxic site because it features multiple individuals of a single taxon. The quality of preservation and the ontogenic (age) range of the specimens helped make ''Coelophysis'' one of the best known of all genera. In 2009, Rinehart ''et al.'' noted that in one case the ''Coelophysis'' specimens were "washed into a topographic low containing a small pond, where they probably drowned and were buried by a sheet flood event from a nearby river." The 30 specimens of ''C. rhodesiensis'' found together in Zimbabwe was also probably the result of a flash flood that swept away a large number of ''Coelophysis'' and buried them quickly and simultaneously as well.

Cultural significance

''Coelophysis'' was the second dinosaur in space, following '' Maiasaura'' (

STS-51-F STS-51-F (also known as Spacelab 2) was the 19th flight of NASA's Space Shuttle program and the eighth flight of Space Shuttle ''Challenger''. It launched from Kennedy Space Center, Florida, on July 29, 1985, and landed eight days later on Au ...

). A ''Coelophysis'' skull from the

was aboard the Space Shuttle Endeavour mission

STS-89 STS-89 was a Space Shuttle mission to the ''Mir'' space station flown by Space Shuttle Space Shuttle Endeavour, ''Endeavour'', and launched from Kennedy Space Center, Florida on 22 January 1998. Crew Crew notes STS-89 was originally scheduled ...

when it left the atmosphere on 22 January 1998. It was also taken onto the space station

Mir ''Mir'' (, ; ) was a space station operated in low Earth orbit from 1986 to 2001, first by the Soviet Union and later by the Russia, Russian Federation. ''Mir'' was the first modular space station and was assembled in orbit from 1986 to ...

before being returned to Earth. Since the discovery of ''Coelophysis'' fossils more than 100 years ago, it is one of the best-known dinosaurs in literature. It was designated as the official state fossil of New Mexico in 1981 and is now the logo of the New Mexico Museum of Natural History.

Notes

References

External links

''Coelophysis''
in the Dino Directory {{Portal bar, Paleontology, Dinosaurs Coelophysoidea Dinosaur genera Rhaetian dinosaurs Chinle Formation Fossil taxa described in 1889 Taxa named by Edward Drinker Cope Dinosaurs of the United States