| Psephosauriscus | |
|---|---|
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Placodontia |
| Superfamily: | †Cyamodontoidea |
| Genus: | †Psephosauriscus Rieppel,2002 |
| Species | |
Psephosauriscus is an extinctgenus ofplacodont reptile from theMiddle Triassic of Israel and Egypt. It is known from bony armor plates that have been found fromMakhtesh Ramon in Israel'sNegev desert andAraif en Naqua on Egypt'sSinai Peninsula. The genus was erected in 2002 as a replacement name for several species of the genusPsephosaurus, which was named in 1957. It includes the speciesP. mosis,P. ramonensis,P. sinaiticus, and a possible fourth species,P. rhombifer. All species, with the exception ofP. ramonensis, were once assigned to the genusPsephosaurus. Remains ofP. mosis andP. ramonensis were found in Makhtesh Ramon, whileP. sinaiticus andP. rhombifer were found in Araif en Naqua.[1]
Armor ofPsephosauriscus is abundant in Middle Triassic limestone in the Sinai and Negev regions, which is comparable to theMuschelkalk of European rock sequences. While the German Muschelkalk contains many nearly complete skeletons of placodonts, the only non-armor skeletal bones from the Middle East are two partial skulls and a fragmentary lower jaw, which cannot be assigned toPsephosauriscus or any other placodont because of their lack of diagnostic features. Remains ofPsephosauriscus come from two deposits called theBeneckeia beds and theCeratites beds, named after their most commonammonite fossils. TheBeneckeia beds date back to theAnisian stage of the Middle Triassic, and theCeratites beds date back to the end of the Anisian and beginning of theLadinian stage.[1]
Swedish paleontologistF. Brotzen described placodont armor from Makhtesh Ramon in 1957, naming the speciesPsephosaurus mosis andPsephosaurus picardi from theBeneckeia andCeratites beds, respectively.P. picardi is now considered anomen dubium because it was based on an impression of the inner surface of the carapace that did not possess any distinct features. In 1959, Austrian paleontologistGeorg Haas namedP. sinaiticus andP. rhombifer from Araif en Naqua.[1]
In 2002, paleontologistOlivier Rieppel erected the genusPsephosauriscus to include most of the species named by Brotzen and Haas, which he considered distinct from thetype species ofPsephosaurus,P. suevicus, named byEberhard Fraas from the Middle Triassic of Germany. Rieppel noted differences between the armor plates ofP. suevicus and the Middle Eastern species that warranted a new genus. However,P. rhombifer could not be assigned with certainty toPsephosauriscus because theholotype specimen described by Haas had since been lost. Rieppel reported additional material from Araif en Naqua that showed similarities toP. rhombifer and the species ofPsephosauriscus, which he tentatively described as a species withinPsephosauriscus,Psephosauriscus cf. rhombifer. Rieppel also namedPsephosauriscus ramonensis as an entirely new species.[1]
The type species ofPsephosauriscus,P. mosis, is known from a single specimen including portions of thecarapace andplastron. Thescutes that cover the armor plates do not have as well-defined a shape as the hexagonal osteoderms that lay underneath them. The osteoderms that form the plastron are relatively large. Some osteoderms have a raised keel. Two distinct ridges along either side of the shell separate the carapace, a lateral wall of smaller osteoderms, and the plastron.
P. ramonensis is known from a partial carapace and connected plastron. The osteoderms of the carapace have smoother edges than most other species ofPsephosauriscus, and lack the keel of species likeP. mosis. The carapace curves into the lateral wall of the body without a separating ridge as inP. mosis, but a lower ridge does separate the lateral wall from the plastron.
P. sinaiticus is known from several armor fragments and larger pieces of the carapace and plastron. The osteoderms of the carapace and plastron are smaller than those of other species. As inP. mosis, two ridges separate run along the side of the shell.
P. cf. rhombifer can be distinguished from the three other species ofPsephosauriscus by the rectangular shape of its scutes. Unlike the smooth shells of other species, the carapace ofP. cf. rhombifer has a bumpy surface; each osteoderm is covered in radiating grooves and has a small depression at its center.[1]
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