| Procyclotosaurus | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | †Temnospondyli |
| Suborder: | †Stereospondyli |
| Clade: | †Capitosauria |
| Family: | †Stenotosauridae |
| Genus: | †Procyclotosaurus Watson, 1958 |
| Species | |
Procyclotosaurus is an extinctgenus ofstenotosauridcapitosauriantemnospondyl. Thetype species isP. stantonensis. In 1904,EnglishpaleontologistArthur Smith Woodward described it as a species ofCapitosaurus,C. stantonensis, based on a partial skull known as R 3174. In 1958, the species was assigned to the new genus. It is known from the LowerKeuper, a European stratigraphic unit that was deposited during thelate Middle Triassic.[1] Fossils have been found fromStaffordshire,England.
Procyclotosaurus was a relatively small temnospondyl. Unlike most other capitosaurs, which have wide and flat skulls,Procyclotosaurus has a deep, wedge-shaped skull. Theotic notch, a notch at the back of the skull, is closed. The tabular horn above the otic notch is narrow and touches thesquamosal bone below the notch.[2] The upper surface of the skull is concave, making it appear dish-shaped. Like other capitosaurs,Procyclotosaurus resemblescrocodilians in that it hasorbits (eye sockets) andnares (nostrils) that are directed upward and slightly elevated.[3]
Procyclotosaurus stantonensis was first classified as a species ofCapitosaurus and was placed in the family Capitosauridae (now known asMastodonsauridae). It was later reassigned as a species ofCyclotosaurus, another mastodonsaurid genus. In 1958, paleontologist D.M.S. Watson placed the species in its own genus,Procyclotosaurus, distinguishing it from bothCapitosaurus andCyclotosaurus on the basis of its deep skull. Watson also found the short suture between the exoccipital and pterygoid bones to be characteristic of the genus. He also noted thatProcyclotosaurus has a crista obliqua, or oblique ridge, on the pterygoid bone at the back of the skull. This ridge is a primitive feature among temnospondyls that is not seen in morederived mastodonsaurids.[4]
The holotype ofProcyclotosaurus, R 3174, is thought to be a young adult. The sutures between the bones of the skull are clearly visible and have not fully closed. The skull is pitted and some of the pits have elongated into troughs, a sign of age. However, these troughs are not as prominent as they would be in an older individual. Paleontologist Roberta L. Paton considered the deep skull and close-set eyes ofProcyclotosaurus to be indicative of a youngCyclotosaurus individual rather than a distinct genus. Therefore, in 1974, Paton reassignedProcyclotosaurus stantonensis toCyclotosaurus. Paton also consideredC. stantonensis to be synonymous with the speciesC. leptognathus, named by English paleontologistRichard Owen, and referred R 3174 toC. leptognathus.[3]
