Coelophysis
Coelophysis | |
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Mounted skeleton at the Cleveland Museum of Natural History | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Family: | †Coelophysidae |
Genus: | †Coelophysis Cope, 1889c |
Type species | |
†Coelurus bauri Cope, 1887a
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Species | |
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Synonyms | |
Genus synonymy
Synonyms of C. bauri
Dubious species designations
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Coelophysis (
Coelophysis was a small, slenderly-built, ground-dwelling,
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.
History of discovery
The type species of Coelophysis was originally named as a species of Coelurus.
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.[19]
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.
Sullivan & Lucas (1999) referred one specimen from Cope's original material of Coelophysis (AMNH 2706) to what they thought was a newly discovered theropod,
Formerly assigned species
"Syntarsus" rhodesiensis was first described by Raath (1969) and assigned to
The genus Syntarsus was named by Raath in 1969 for the type species
Description
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
Coelophysis had narrow hips, arms adapted for grasping prey, and narrow feet.
Coelophysis had a long and narrow head (approximately 270 mm (0.9 ft)), with large, forward-facing eyes that afforded it
Coelophysis had an elongated snout with large
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[47]), and the anteroposterior length of the ventral lacrimal process is greater than 30% of its height.[48]
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.[35] 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.[43] Bristowe and Raath (2004) concluded that C. bauri differs from M. rhodesiensis in having a longer maxillary tooth row.[48] Barta et al. (2018) concluded that C. bauri differed from M. rhodesiensis in that it bears its 5th metacarpal.[30] Griffin (2018) concluded that C. bauri differs from M. rhodesiensis in several differences in the musculature of the limbs.[38]
Classification
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.[19] M. rhodesiensis was referred to Coelophysis for several years, but it is likely its own genus[38][30] and is known from the early Jurassic of southern Africa. A third possible species is Coelophysis kayentakatae, previously referred to the genus Megapnosaurus,[50][51] 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.[49][30][52]
Paleobiology
Feeding
The teeth of Coelophysis were typical of predatory dinosaurs, as they were blade-like, recurved, sharp, jagged, and finely serrated on both the
It has been suggested that C. bauri was a
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.[57]
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.[58] There is a tendency to see this massive congregation of animals as evidence for huge packs of Coelophysis roaming the land.[16] 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 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 run of fish, being later buried in a catastrophic flash flood[16][58] or a drought.[16]
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.[27][59][60]
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) and concluded that Coelophysis juveniles grew rapidly, especially during the first year of life.[41] 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.[41] It was also thought that, as soon as they were hatched, they would have to fend for themselves.[16]
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.[61] 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.[17] Historically, many arguments have been made that this represents some sort of dimorphism in the population of Coelophysis, probably sexual dimorphism.[34][17][62][63] Raath agreed that dimorphism in Coelophysis is evidenced by the size and structure of the arm.[62] 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.[41] 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.[64]
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.[65]
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.[41][66]
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.[67]
In C. rhodesiensis, healed fractures of the
Ichnology
Edwin H. Colbert has suggested that the theropod footprints referred to the
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[41] 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,[72][16] but Thomas Holtz Jr. interpreted that it was during the Rhaetian stage from approximately 204 to 201.6 million years ago.[73]
C. rhodesiensis has been recovered in the
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.[74]
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.[75]
In the upper sections of the Chinle Formation where Coelophysis is found, dinosaurs were rare. So far, only
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 and, indeed, the Petrified Forest of nearby Arizona 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.[83] 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."[41]
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.[27][59][60]
Cultural significance
Coelophysis was the second dinosaur in space, following Maiasaura (STS-51-F).[84] 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 22 January 1998. It was also taken onto the space station Mir before being returned to Earth.[84][85]
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][86]
References
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External links
- Coelophysis Archived 25 September 2006 at the Wayback Machine in the Dino Directory