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.

Paleobiology

Feeding

thumb|left|Bones in a skeleton of C. bauri at the [[American Museum of Natural History, now interpreted as those of a crocodylomorph]]

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.

Pack behavior

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.

Growth and sexual dimorphism

thumb|left|Juvenile skeleton of C. bauri at the [[New Mexico Museum of Natural History and Science]]

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.

Reproduction

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.

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.

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.

Ichnology

thumb|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. 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

thumb|left|Restoration of Coelophysis and contemporary animals

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 but Thomas Holtz Jr. interpreted that it was during the Rhaetian stage from approximately 204 to 201.6 million years ago.

C. rhodesiensis has been recovered in the Upper Elliot 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.

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 and Daemonosaurus are known, the terrestrial fauna being dominated instead by other reptiles like the rhynchocephalian Whitakersaurus, the pseudosuchian Revueltosaurus, the aetosaurs Desmatosuchus, Typothorax and Heliocanthus, the crocodilomorph Hesperosuchus, the "rauisuchians" Shuvosaurus, Effigia, and Vivaron, along with other rare components like the dinosauriform Eucoelophysis and the amniote Kraterokheirodon. In the waterways there are the phytosaur Machaeroprosopus, the archosauromorph Vancleavea, the amphibians Apachesaurus and the fishes Reticulodus, Arganodus, and Lasalichthyes. 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." 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.

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

  • Coelophysis in the Dino Directory