Emydops
Emydops is an extinct genus of dicynodont therapsids from the Middle Permian to Late Permian of what is now South Africa. The genus is generally small and herbivorous, sharing the dicynodont synapomorphy of bearing two tusks. In the following years, the genus grew to include fourteen species. Many of these species were erected on the basis of differences in the teeth and the positioning of the frontal and parietal bones. A 2008 study narrowed Emydops down to two species, E. arctatus (first described by English paleontologist Richard Owen as Kistecephalus arctatus in 1876) and the newly described E. oweni. History and discovery Emydops was first discovered and named in 1912 by Robert Broom, in which he described the species E. minor. Although later on it was suggested that the genus included 13 more species, Frobisch and Reisz (2008) suggests that only E. oweni and E. arctatus are the only valid species of Emydops. With the appearance of E. minor marking the beginning of the stratigraphic range of Emydops in the Late Permian-aged Tropidostoma Assemblage Zone from the Karoo Basin of South Africa, it is argued that a specimen found in the vicinity of the Middle Permian to Late Permian Tapinocephalus Assemblage Zone and Middle Permian Pristerognathus Assemblage Zone of Beauford West belongs to Emydops. Whether the specimen is from the Tapinocephalus Assemblage Zone or Pristerognathus Assemblage Zone, both indicate that Emydops stratigraphic range began earlier than it has been previously accepted. Description Skull The skull of Emydops is small, up to 5 cm (2 in) long. The premaxillae and maxillae of Emydops are less pronounced than those of more mature dicynodonts, and they are generated downward as a distinct outer rim that is most developed around the canines. Anteriorly, the rim continues slightly downwards and forms the tip of the upper beak. The orbits are positioned far anteriorly in the skull, and face forward and upward. The temporal region is large in proportion to the face and provides attachment for the laterodorsal trigeminal musculature of enormous bulk. In dorsal view, the temporal vacuities are described to be large and the ventrolateral region of the cheek is deeply excavated. Convergently evolved from cynodonts, dicynodonts also have a secondary palate which consists of a broad, flat, horizontal plate formed anteriorly by the palatines. Additionally, it extends posteriorly by the palatines, which dip gently downward to the rear. The reflected lamina of the angular bone of Emydops is large and fan-shaped, like other small dicynodonts. However, unlike many dicynodonts, the reflected lamina of the angular bone of Emydops has a broad, thin, unsupported sheet that terminates in a long, free border rather than the sheet folding and converging anteriorly toward a marginal thickening on the angular body. As well, a broadened lateral dentary shelf on the lower jaw serves as another distinguishing feature of the genus. Dentition Most skulls of Emydops bear a pair of caniniform tusks, diagnostic of dicynodonts, There are generally three postcanine teeth present in the upper jaw of Emydops.