Coelophysis

One of the earliest known dinosaurs, Coelophysis (see-law-FYS-iss) meaning "hollow form" in reference to its hollow bones (Greek koilos meaning 'hollow' and physis meaning 'form') is a small, carnivorous biped from North America. It first appeared in the Late Triassic Period, around 210 million years ago.

Description

Coelophysis bauri is the earliest well known dinosaur. C. bauri was a lightly built dinosaur, between two to three meters in length, and less than a meter tall at the hips. The name Coelophysis means "hollow form" or "hollow process, so named because of its hollow limb bones.

Despite being an early dinosaur, the evolution of the theropod body form had already advanced greatly from creatures like Herrerasaurus and Eoraptor. Coelophysis had an elongated snout with large fenestrae which 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 torso of Coelophysis conforms to the basic theropod body shape, but the pectoral girdle displays some interesting 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, the fourth embedded in the flesh of the hand.

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 the Dinosauria. The hindlimb ended in a three-toed foot (pes), with a raised hallux.

The tail of Coelophysis had an unusual structure within its prezygapophysis that formed a semi-rigid lattice, apparently to stop the tail from moving up and down (Gay, 2001). This may have let tail act as a rudder or counterbalance when the animal was maneuvering.

Behavior

Evidence for behavior in the fossil record is always patchy and this also holds true for Coelophysis. Despite the huge number of specimens available from Ghost Ranch, only some basic deductions about its behavior can be gleaned.

Coelophysis was probably opportunistic, catching live prey and scavenging. The teeth were typical of predatory dinosaurs, blade-like and recurved with fine serrations on both anterior and posterior edges. They were rooted in the jaws in sockets, and were being continually replaced throughout the animal's life.

Since our knowledge of Coelophysis comes basically from the specimens excavated from Ghost Ranch, there is a tendency to see this massive congregation of animals as evidence for huge packs of Coelophysis roaming the land (à la Walking with Dinosaurs). There is no evidence for this. What the deposit does tell us is that large numbers of Coelophysis, along with 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 big spawning run of fish, then becoming buried in a catastrophic flash flood. This reconstructed incident inspired the scenario of the first episode of Walking with Dinosaurs.

Some people, both lay and professional, have suggested that C. bauri was a cannibal. While this possibility cannot be ruled out, the evidence from the commonly-cited examples does not appear to hold up to scrutiny (Gay, 2002). There may be other evidence coming to light that may show stomach contents from some of these specimens, which might bring greater resolution to the subject (Reinhart et al., 2005).

Two forms of Coelophysis have been found, a more graceful form and a slightly more robust form. Opinion among paleontologists is now that these were female and male variants (see: sexual dimorphism) (Colbert, 1989, 1990; Paul, 1988; Gay, 2005).

Classification

Coelophysis is a distinct taxonomic unit (genus), composed of a single species, C. bauri. Two additional species were originally described in addition to C. bauri, C. longicollis, and C. willistoni, however they are not diagnostic and are considered synonymous with C. bauri. C. rhodesiensis is probably part of this generic complex, and is known from the Jurassic of southern Africa (see below for more). Coelophysis is a clade within the Coelophysidae.

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 (Lucas, 1991), to the Ghost Ranch Quarry specimens.

Since the numerous, well-preserved Ghost Ranch specimes 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 submitted to have the type specimen of Coelophysis transferred from the poorly-preserved, original specimen to one of the well-preserved Ghost ranch specimens. 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 original type specimen was given a new genus and species name, Eucoelophysis baldwini (Sullivan and Lucas, 1999) and the name Coelophysis became a nomen conservandum ("conserved name").

In addition to all of this, there is a competing controversy with another coelophysoid, Syntarsus, which many regard to be cogeneric with Coelophysis (Downs, 2000; Paul, 1988). To make matters more confusing, Paul (1993) suggested that Coelophysis should be placed in Syntarsus to get around the above-mentioned taxonomic confusion.

In a situation affecting many dinosaur genera, many specimens were originally classified as new species but were in fact species of Coelophysis. For example, Prof. Mignon Talbot's 1911 discovery which she labeled Podokesaurus holyokensis, may be related to (or is) Coelophysis. In addition, C. posthumus, named by Friedrich von Huene in 1908, also needs reclassification and is tentatively titled Halticosaurus longotarsus at the moment.

While debate is still intense over the matter, some scientists believe that the Coelophysidae are the ancestors to all later theropod groups, including modern birds.

History of discovery

Cope first named Coelophysis in 1889 during his competition to name species with Othniel Charles Marsh, known as the Bone Wars. An amateur fossil collector, David Baldwin, had found the first remains of the dinosaur in 1881. The type species, C. bauri was named for Baur, one of Cope's many fossil collectors who supplied him. However, these first finds were small and there was certainly no complete picture of this new dinosaur.

In 1947, a big graveyard of Coelophysis fossils were found in New Mexico, at the Ghost Ranch, close to the original find (see above for history of classification). So many fossils together were probably the result of a flash flood, which swept away a big aggregation which had collected around the last accessible water in the area, or to feed on a big spawning run of fish, and buried it at once. In fact, it seems such flooding was commonplace during this period of the Earth's history, and indeed the Petrified Forest of nearby Arizona is caused by a preserved log jam of tree trunks caught in one such flood. Edwin H. Colbert made a comprehensive study (Colbert, 1989) of all the fossils found up to that date, and it is from him that we take most of our information about Coelophysis.

Since then, more skeletons have been found in Arizona, New Mexico and an as-yet unconfirmed specimen from Utah, including both adults and juveniles. The deposits where Coelophysis has been discovered date from the late Carnian to the early Norian faunal stages.

Trivia

Coelophysis was the second dinosaur in space. Although Maiasaura had been taken into space three years earlier, 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.

Coelophysis is also the state fossil of New Mexico.

In Popular Culture

Coelophysis are featured in Walking With Dinosaurs as resourceful little dinosaurs. When Dinosaurs Roamed America features this creature similarily, but meeker, able to hunt only insects.

References

Colbert, Edwin. 1989. The Triassic Dinosaur Coelophysis. Museum of Northern Arizona Bulletin.
Colbert, Edwin. 1990. in Dinosaur Systematics.
Downs, Alex. 2000. in Dinosaurs of New Mexico, New Mexico Museum of Natural History Bulletin.
Gay, Robert J. 2001. An unusual adaptation in the caudal vertebrae of Coelophysis bauri (Dinosauria: Theropoda). PaleoBios 21: supplement to number 2. Page 55.
Gay, Robert J. 2002. The myth of cannibalism in Coelophysis bauri. Journal of Vertebrate Paleontology 22(3); 57A
Gay, R. 2005. Sexual Dimorphism in the Early Jurassic Theropod Dinosaur Dilophosaurus and a Comparison with Other Related Forms; pp. 277-283 in K. Carpenter (ed.), The Carnivorous Dinosaurs. Indiana University Press, Bloomington, IN.
Paul, Gregory. 1988. Predatory Dinosaurs of the World
Paul, Gregory. 1993. in New Mexico Museum of Natural History Bulletin.

External links

"Coelophysis ". DinoData.
about the Coelophysis finds at Ghost Ranch and what happened to them.

Coelophysoids | North American dinosaurs | Triassic dinosaurs

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