Petrolacosaurus
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Petrolacosaurus Temporal range: Pennsylvanian, 302 Ma |
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| Petrolacosaurus kansensis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Subclass: | Diapsida |
| Order: | Araeoscelida |
| Family: |
Petrolacosauridae Peabody, 1952 |
| Genus: |
Petrolacosaurus Lane, 1945 |
| Species: | Petrolacosaurus kansensis |
Petrolacosaurus was a small, 40-centimetre (16 in) long reptile, and the earliest known diapsid. It is at the base of the largest reptilian radiation that includes eosuchians, thecodonts, rhynchosaurs, pterosaurs, dinosaurs, and eventually birds.
The first Petrolacosaurus fossil was found in 1932 in Garnett, Kansas by a field expedition from the University of Kansas Natural History Museum. The party consisted of Henry H. Lane, Claude Hibbard, David Dunkle, Wallace Lane, Louis Coghill, and Curtis Hesse. Unfortunately, no field notes or documentation of their discovery are available.
Petrolacosaurus was found preserved within a layer of laminated shale that was also plant bearing. The strata that the remains were found in was of Upper Pennsylvanian age (approximately 323-298 ma). The fossil itself is estimated to be approximately 302 million years old.
Specimens reveal that Petrolacosaurus had a slightly elongated skull with two temporal fenestrae. The upper temporal fenestra is located posteriorly to an enlarged orbit. This is a distinctly diapsid character.
On the dentary, there are marginal teeth, displaying a primitive type of shallow implantation. There are also two larger teeth on the premaxilla, the function of which will be explained below in more detail. The palatal arrangement bears close resemblance to Youngoides.
There are seven elongated cervical vertebrae, 2 sacrals, and 60 caudal vertebrae. The number and placement of the vertebrae show that Petrolacosaurus was a long-necked reptile with a shorter torso. The number and spool-like shape of the vertebrae, in addition to the poses that the reptiles died in, show that they were also very flexible creatures.
The vertebral centra are amphicoelous in shape and have large, ventro-lateral depressions. A similar depression can be seen on the massive neural arches, running from the prezygapophyses to the postzygapophysis. These depressions allowed the vertebral column to be lighter while still retaining a sturdy build.
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Wikipedia