Целофизис: Ранний теропод динозавр позднего триаса

Genus of theropod dinosaurs from the late Triassic

Automatic taxobox
| fossil range = Late Triassic (middle to late Norian),
| image = Coelophysis bauri mount. jpg
| image caption = Mounted skeleton at the Cleveland Museum of Natural History
| taxon = Coelophysis
| authority = Cope, 1889c
| type species = Coelurus bauri
| type species authority = Cope, 1887a
| subdivision ranks = Species
| subdivision = * Coelophysis bauri (Cope, 1887a) Cope, 1889c
| synonyms = collapsible list|bullets = true
|title=Genus synonymy
|Podokesaurus? Talbot, 1911
|Rioarribasaurus Hunt & Lucas, 1991) is a genus of coelophysid theropod dinosaur that lived approximately 215 to 208.5 million years ago during the Late Triassic period from the middle to late Norian age in what is now the southwestern United States. Megapnosaurus was once considered to be a species within this genus, but this interpretation has been challenged since 2017 and the genus Megapnosaurus is now considered valid. Coelophysis was a small, slenderly built, ground dwelling, bipedal carnivore 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 Late Triassic and Early Jurassic formations. The type species C. bauri, originally given to the genus Coelurus by Edward Drinker Cope 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.

The type species of Coelophysis was originally named as a species of Coelurus. An amateur fossil collector working for Cope, David Baldwin, had found the first remains of the dinosaur in 1881 in the Chinle Formation in northwestern New Mexico. The name Coelophysis comes from the Greek words κοῖλος/koilos (meaning 'hollow') and φύσις/physis (meaning 'form'), together "hollow form", which is a reference to its hollow vertebrae. Since the numerous well preserved Ghost Ranch specimens were used as Coelophysis in most of the scientific literature, the use of Rioarribasaurus would have been very inconvenient for researchers. So, a petition was given to have the type specimen of Coelophysis transferred from the poorly preserved original specimen to one of the well preserved Ghost Ranch specimens. This would make Rioarribasaurus a definite synonym of Coelophysis, specifically a junior objective synonym. In the end, the International Commission on Zoological Nomenclature (ICZN) voted to make one of the Ghost Ranch samples the actual type specimen for Coelophysis and dispose of the name Rioarribasaurus altogether (declaring it a nomen rejectum, or "rejected name"), thus resolving the confusion. The name Coelophysis became a nomen conservandum ("conserved name"). In a situation affecting many dinosaur taxa, some more recently discovered fossils were originally classified as new genera, but may be species of Coelophysis. For example, Prof. Mignon Talbot's 1911 discovery, which she named Podokesaurus holyokensis, has long been considered to be related to Coelophysis and some modern scientists consider Podokesaurus a synonym of Coelophysis. Another specimen from the Portland Formation of the Hartford Basin, now at the Boston Museum of Science, has also been referred to Coelophysis. The specimen consists of sandstone casts of a pubis, tibia, three ribs, and a possible vertebra that probably originated in a quarry in Middletown, Connecticut. However, both the type specimen of Podokesaurus and the Middletown specimen are typically considered indeterminate theropods today. Sullivan & Lucas (1999) referred one specimen from Cope's original material of Coelophysis (AMNH 2706) to what they thought was a newly discovered theropod, Eucoelophysis. However, subsequent studies have shown that Eucoelophysis was misidentified and is actually a silesaurid, a type of non dinosaurian ornithodiran closely related to Silesaurus.

"Syntarsus" rhodesiensis was first described by Raath (1969) and assigned to Podokesauridae. The taxon "Podokesauridae", was abandoned because its type specimen was destroyed in a fire and can no longer be compared to new finds. Over the years, paleontologists assigned the genus to Ceratosauridae (Welles, 1984), Procompsognathidae (Parrish and Carpenter, 1986), and Ceratosauria (Gauthier, 1986). In 2004, "Syntarsus" was found to be synonymous with Coelophysis by Tykoski and Rowe (2004). Ezcurra and Novas (2007) and Ezcurra (2007) also concluded that "Syntarsus" was synonymous with Coelophysis. In a phylogenetic analysis by Ezcurra (2017), Megapnosaurus was recovered in a clade with Segisaurus and Camposaurus, supporting the generic distinction of Megapnosaurus. This was supported by Barta and colleagues in 2018, noting that Coelophysis still bears the vestigial 5th metacarpal, a feature absent in Megapnosaurus. The genus Syntarsus was named by Raath in 1969 for the type species Syntarsus rhodesiensis from Africa and later applied to the North American Syntarsus kayentakatae. 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. Mortimer (2012) pointed out that "Paleontologists might have reacted more positively if the replacement name (Megapnosaurus) hadn't been facetious, translating to "big dead lizard". Yates (2005) analyzed Coelophysis and Megapnosaurus and concluded that the two genera are almost identical, suggesting that Megapnosaurus was possibly synonymous with Coelophysis. In 2004, Raath co authored two papers in which he argued that Megapnosaurus (formerly Syntarsus) was a junior synonym of Coelophysis. Downs (2000) examined Camposaurus and concluded that it was a junior synonym of Coelophysis because of its similarity to some of the Coelophysis Ghost Ranch specimens. Barta et al. (2018) concluded that C. bauri differed from M. rhodesiensis in that it bears its 5th metacarpal and was more than a meter tall at the hips. Gregory S. Paul (1988) estimated the weight of the gracile form at and the weight of the robust form at , Coelophysis was a bipedal, carnivorous, theropod dinosaur and a fast, agile runner. Despite its basal position within Theropoda, 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 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 pelvis and hindlimbs of C. bauri are also slight variations on the theropod body plan. It has the open acetabulum and straight ankle hinge that define Dinosauria. The leg ended in a three toed foot (pes) with a raised dewclaw (hallux). 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 had a long and narrow head (approximately ), with large, forward facing eyes that afforded it stereoscopic vision and, as a result, excellent depth perception. Rinehart et al. (2004) described the complete sclerotic ring 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. ), 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.

Theropod cladogram based on the phylogenetic analyses conducted by Ezcurra et al. (2020). 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. from the Kayenta Formation 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.

The teeth of Coelophysis were typical of predatory dinosaurs, as they were blade like, recurved, sharp, jagged, and finely serrated on both the anterior 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. It has been suggested that C. bauri was a cannibal, based on supposed juvenile specimens found "within" the abdominal cavities of some Ghost Ranch specimens. 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.

[[File:CMNH Coelophysis Block. jpg|thumbnail|The Cleveland Museum of Natural History's Coelophysis block, originally American Museum of Natural History block XII collected by Colbert in 1948. There is a tendency to see this massive congregation of animals as evidence for huge packs of Coelophysis roaming the land.

Rinehart (2009) assessed the ontogenic growth of this genus using data gathered from the length of its upper leg bone (femur) and concluded that Coelophysis juveniles grew rapidly, especially during the first year of life. 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. 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. 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.

thumb|Two C. bauri casts mounted at the Denver Museum of Nature and Science
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.

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. In C. rhodesiensis, healed fractures of the tibia and metatarsus have been observed, but are very rare. "[T]he supporting butresses of the second sacral rib" in one specimen of Syntarsus rhodesiensis showed signs of fluctuating asymmetry. Fluctuating asymmetry 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.