| Bidentalia | |
|---|---|
 | |
| Skull ofDicynodon | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | †Anomodontia |
| Clade: | †Dicynodontia |
| Clade: | †Therochelonia |
| Clade: | †Bidentalia Owen,1876 |
Bidentalia is a group ofdicynodonttherapsids. Bidentalia was one of the first names used to describe dicynodonts; the group was established in 1876, while the name "bidentals" dates back as far as 1845. With the increasing prominence ofphylogenetics, the group was redefined as aclade in 2009. Bidentalia is now considered astem-based taxon that includes all taxa more closely related toAulacephalodon bainii andDicynodon lacerticeps thanEmydops arctatus.
In 1845, South African geologistAndrew Geddes Bain described the first known dicynodonts as "bidentals" for their two prominent tusks.[1] "Bidental" was the first name ever used for a group of non-mammaliansynapsids.[2] The name Dicynodontia, which is more commonly used to refer to these animals, was erected by English paleontologistRichard Owen in 1860.[3] Realizing that Bain's "bidentals" predated his "dicynodonts", Owen named Bidentalia in 1876 as a replacement name for Dicynodontia. Owen described Bidentalia as reptiles with "a long ever-growing tusk in each maxillary; premaxillaries connate, forming with the lower jaw a beak-shaped mouth, probably sheathed with horn. Sacrum of more than two vertebrae; trunk-vertebrae amphicoelian; limbs ambulatory."[4] At this time, Bidentalia included three main species:Dicynodon lacerticeps,Dicynodon bainii, andPtychognathus declivis. The twoDicynodon species were named in 1845, just before Bain described his bidentals.Ptychognathus was named in 1859, and is now calledLystrosaurus. In the following years Dicynodontia became the preferred name for these reptiles and Bidentalia quickly fell out of use.[2]
Bidentalia was reinstated as aclade in 2009.[2] It was used to include alltherochelonians more closely related toDicynodon than toemydopoids (a group of morebasal dicynodonts). As a clade, Bidentalia forms a more inclusive group than it did under Owen's use. Owen's Bidentalia was equivalent to Dicynodontia, which today is used as a much larger group encompassing all dicynodonts. In its current use, Bidentalia includes two major subgroups,Cryptodontia andDicynodontoidea.
Bidentalia originated in theGuadalupian epoch of thePermian and quickly spread worldwide, with early species known from both Brazil and Russia. However, they were conspicuously absent from Africa despite its well-known Permian fauna until thelate Permian.[5] The oldest and most basal known bidentalian isRastodon.
Bidentalia is divided into two major groups, the Cryptodontia and the Dicynodontoidea, as well as a small number of basal genera such asElph andRastodon[5] However, the Cryptodontia may be paraphyletic. Below is acladogram showing the phylogeny of Bidentalia from a recent study, Kammereret al. (2011):[6]
