''Rhipaeosaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

nycteroleterid Nycteroleteridae is a family of procolophonian parareptilians (extinct early reptiles) from the Middle to Late Permian of Russia and North America. They are sometimes classified as a sister group to pareiasaurids (but see ''Classification)'' ...

parareptile Parareptilia ("at the side of reptiles") is a subclass or clade of basal sauropsids (reptiles), typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near th ...

known from an articulated skeleton from the mid

Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...

of European Russia. It contained a single

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, ''Rhipaeosaurus tricuspidens''. A

bayesian Thomas Bayes (/beɪz/; c. 1701 – 1761) was an English statistician, philosopher, and Presbyterian minister. Bayesian () refers either to a range of concepts and approaches that relate to statistical methods based on Bayes' theorem, or a followe ...

analysis suggests that it is more closely related to pareiasaurs than to the other nycteroleterids, due to skull and tooth features. For this reason, "Nycteroleteridae" may be a

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

rather than a clade, unless redefined to exclude ''Rhipaeosaurus''.

Description

''Rhipaeosaurus'' is around a meter long, larger than any other "nycteroleterids" and closer in size to later pareiasaurs. Postcranial remains were similar to ''

Macroleter ''Macroleter'' is an extinct genus of nycteroleterid parareptile which existed in Oklahoma and Russia during the upper Permian period. It was a quite generalized primitive reptile, in many ways resembling their amphibian ancestors. It was firs ...

'', though the limbs were more robust and the ankle bones were unfused. The teeth were flattened and tricuspid (possessing three cusps), seemingly intermediate in form between the one- or two-cusped teeth of earlier nycteroleterids and the multi-cusped teeth of pareiasaurs. Many components of the partial skull and skeleton (which was originally fairly complete) had been lost or degraded between 1940 and 2012, obscuring most aspects of its anatomy.

History

''Rhipaeosaurus'' was first described in 1940, from a fairly complete skeleton found in the

Ural Mountains The Ural Mountains ( ; rus, Ура́льские го́ры, r=Uralskiye gory, p=ʊˈralʲskʲɪjə ˈɡorɨ; ba, Урал тауҙары) or simply the Urals, are a mountain range that runs approximately from north to south through western ...

of Russia. The name 'Rhipaeosaurus' comes from 'Ῥιπαεος' 'Rhipaeos, a range of mountains in

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities ...

thought to be the Urals, and '', meaning 'lizard'. 'Tricuspidens' refers to its three-cusped teeth. ''Rhipaeosaurus taxonomic history has been full of difficulties. At first it was placed in its own

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

, the Rhipaeosauridae, and considered the type species. Other taxa, such as '' Parabradysaurus'' and ''

Leptoropha ''Leptoropha'' is an extinct genus of aquatic seymouriamorph known from the Middle Permian of Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the larges ...

,'' later joined it in this family. However, when more remains of these additional taxa were found, they were determined not to be rhipaeosaurids at all. ''Parabradysaurus'' was found to be an estemnosuchid, more closely related to mammals, and ''Leptoropha'' was identified as a

seymouriamorph Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are s ...

amphibian. ''Rhipaeosaurus'''s status as a parareptile is still considered relatively stable, either as a basal nycteroleterid or a transitional taxon between other "nycteroleterids" and pareiasaurus.

References

External links

The Paleobiology Database

Permian reptiles of Europe Pareiasauromorphs Fossil taxa described in 1940 Prehistoric reptile genera {{paleo-reptile-stub