Bidentalia

Bidentalia is a group of dicynodont therapsids. 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 of phylogenetics, the group was redefined as a clade in 2009. Bidentalia is now considered a stem-based taxon that includes all taxa more closely related to Aulacephalodon bainii and Dicynodon lacerticeps than Emydops arctatus.

==History== In 1845, South African geologist Andrew Geddes Bain described the first known dicynodonts as "bidentals" for their two prominent tusks. "Bidental" was the first name ever used for a group of non-mammalian synapsids. The name Dicynodontia, which is more commonly used to refer to these animals, was erected by English paleontologist Richard Owen in 1860. 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." At this time, Bidentalia included three main species: Dicynodon lacerticeps, Dicynodon bainii, and Ptychognathus declivis. The two Dicynodon species were named in 1845, just before Bain described his bidentals. Ptychognathus was named in 1859, and is now called Lystrosaurus. In the following years Dicynodontia became the preferred name for these reptiles and Bidentalia quickly fell out of use.