Coelophysis

The famed Coelophysis quarry of Ghost Ranch, as it appears in 2019.

The type species of Coelophysis was originally named as a species of Coelurus.[12] Edward Drinker Cope first named Coelophysis in 1889 to name a new genus, outside of Coelurus and Tanystropheus, which C. bauri was previously classified in, for C. bauri, C. willistoni, and C. longicollis.[13] 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.[14] Early in 1887, Cope referred the specimens collected to two new species, C. bauri and C. longicollis of the genus Coelurus. Later on in 1887, Cope reassigned the material to a yet another genus, Tanystropheus. Two years later, Cope corrected his classification after realizing differences in the vertebrae and named Coelophysis, with C. bauri as the type species,[13] which was named for Georg Baur, a comparative anatomist whose ideas were similar to Cope's.[14][15] 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.[13][16] However, the first finds were too poorly preserved to give a complete picture of the new dinosaur. In 1947, a substantial "graveyard" of Coelophysis fossils was found by George Whitaker, the assistant of Edwin H. Colbert, in New Mexico, at Ghost Ranch, close to the original find. American Museum of Natural History paleontologist Edwin H. Colbert conducted a comprehensive study[17] of all the fossils found up to that date and assigned them to Coelophysis. The Ghost Ranch specimens were so numerous, including many well-preserved and fully articulated specimens, that one of them has since become the diagnostic, or type specimen, for the entire genus, replacing the original, poorly preserved specimen.[18]

Two Ghost Ranch specimens preserved together, including the neotype, AMNH

"Syntarsus" rhodesiensis was first described by Raath (1969) and assigned to Podokesauridae.[19] 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.[20] In a phylogenetic analysis by Ezcurra (2017), Megapnosaurus was recovered in a clade with Segisaurus and Camposaurus, supporting the generic distinction of Megapnosaurus.[21] This was supported by Barta and colleagues in 2018, noting that Coelophysis still bears the vestigial 5th metacarpal, a feature absent in Megapnosaurus.[22]

Size of C. bauri compared to a human

Coelophysis is known from a number of complete fossil skeletons of the species C. bauri. This lightly built dinosaur measured up to 3 metres (9.8 ft) long[23] and was more than a meter tall at the hips. Gregory S. Paul (1988) estimated the weight of the gracile form at 15 kg (33 lb) and the weight of the robust form at 20 kg (44 lb),[24] but later presented a higher estimate of 25 kg (55 lb).[25] Coelophysis was a bipedal, carnivorous, theropod dinosaur and a fast, agile runner.[26] 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.[27]

Coelophysis had narrow hips, arms adapted for grasping prey, and narrow feet.[28] Its neck and tail were long and slender.[5] 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.[29]

C. bauri profile

Coelophysis had a long and narrow head (approximately 270 mm (0.9 ft)), 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.[30] 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.[26]

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 curve. The braincase is known in Coelophysis bauri, but little data could be derived because the skull was crushed.[28] 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.[17]

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.[36] M. rhodesiensis was referred to Coelophysis for several years, but it is likely its own genus[34][22] and is known from the early Jurassic of southern Africa. A third possible species is Coelophysis kayentakatae, previously referred to the genus Megapnosaurus,[37][38] 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.[35][22][39]

In the early 1990s, there was debate over the diagnostic characteristics of the first specimens collected, compared to the material excavated at the Ghost Ranch Coelophysis quarry. Some paleontologists were of the opinion that the original specimens were not diagnostic beyond themselves and, therefore, that the name C. bauri could not be applied to any additional specimens. They therefore applied a different name, Rioarribasaurus, to the Ghost Ranch quarry specimens.[36]

Cast of the neotype specimen AMNH FR 7224, Redpath Museum

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.[12] 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").[18]

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,[40] which she named Podokesaurus holyokensis, has long been considered to be related to Coelophysis[41] and some modern scientists consider Podokesaurus a synonym of Coelophysis.[1] Another specimen from the Portland Formation of the Hartford Basin, now at the Boston Museum of Science, has also been referred to Coelophysis.[42][43] 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.[44]

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.[45] However, subsequent studies have shown that Eucoelophysis was misidentified and is actually a primitive, non-dinosaurian ornithodiran closely related to Silesaurus.[46]

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.[19] It was renamed by American entomologist Dr. Michael Ivie (Montana State University of Bozeman), Polish Australian Dr. Adam Ślipiński, and Polish Dr. Piotr Węgrzynowicz (Muzeum Ewolucji Instytutu Zoologii PAN of Warsaw), the three scientists who discovered that the genus name Syntarsus was already taken by a colydiine beetle described in 1869.[47] 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".[48] Yates (2005) analyzed Coelophysis and Megapnosaurus and concluded that the two genera are almost identical, suggesting that Megapnosaurus was possibly synonymous with Coelophysis.[49] In 2004, Raath co-authored two papers in which he argued that Megapnosaurus (formerly Syntarsus) was a junior synonym of Coelophysis.[1] Megapnosaurus was regarded by Paul (1988) and Downs (2000) as being congeneric with Coelophysis.[24][33] In 1993, Paul then suggested that Coelophysis should be placed in Megapnosaurus (then known as Syntarsus) to get around the above-mentioned taxonomic confusion.[50] 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.[33] However, a reassessment of the Camposaurus holotype by Martin Ezcurra and Stephen Brusatte, published in 2011, revealed a pair of autapomorphies in the holotype, indicating that C. arizonensis was not a synonym of C. bauri, although it was a close relative of M. rhodesiensis.[51] Barta et al. (2018) concluded that C. bauri differed from M. rhodesiensis in that it bears its 5th metacarpal[22] and several features in the musculature of the limbs according to Griffin (2018).[34]

Grallator from Middletown, Connecticut

Edwin H. Colbert has suggested that the theropod footprints referred to the ichnogenus Grallator, located in the Connecticut River Valley across Connecticut and Massachusetts, may have been made by Coelophysis.[68] 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.[69] 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.[70]

Restoration showing hypothetical wattle and feathers.

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[26] 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 Norian stage of the Late Triassic,[71][16] but Thomas Holtz Jr. interpreted that it was during the Rhaetian stage from approximately 204 to 201.6 million years ago.[72]

C. rhodesiensis has been recovered in the Upper Elliott Formation in the Cape 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.[73]

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.[74]

In the upper sections of the Chinle Formation where Coelophysis is found, dinosaurs were rare. So far, only Chindesaurus and Daemonosaurus[75] are known, the terrestrial fauna being dominated instead by other reptiles like the rhynchocephalian Whitakersaurus,[76] the pseudosuchian Revueltosaurus, the aetosaurs Desmatosuchus, Typothorax and Heliocanthus, the crocodilomorph Hesperosuchus, the "rauisuchians" Shuvosaurus,[77] Effigia,[78] and Vivaron,[79] along with other rare components like the dinosauriform Eucoelophysis[80] and the amniote Kraterokheirodon. In the waterways there are the phytosaur Machaeroprosopus, the archosauromorph Vancleavea, the amphibians Apachesaurus[77] and Koskinonodon,[81] and the fishes Reticulodus, Arganodus, and Lasalichthyes.[77]

Coelophysis was the second dinosaur in space, following Maiasaura (STS-51-F).[83] A Coelophysis skull from the Carnegie Museum of Natural History was aboard the Space Shuttle Endeavour mission STS-89 when it left the atmosphere on January 22, 1998. It was also taken onto the space station Mir before being returned to Earth.[83][84]

Being over 100 years old, Coelophysis 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.[12][85]

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• Coelophysis Archived 25 September 2006 at the Wayback Machine in the Dino Directory