Robertia
Robertia is an extinct genus of small herbivorous dicynodonts from the Middle to Late Permian of South Africa, between 260 and 265 million years ago.[1] It is a monospecific genus,[1] consisting of the type-species R. broomiana, which was classified by Lieuwe Dirk Boonstra in 1948 and named in honor of Robert Broom for his study of South African mammal-like reptiles.[2]
Robertia had characteristic caniniform tusks and few, small teeth on the maxillary and dentary table.[3] Its beak and the propalinal movement of the jaw, as with other dicynodonts, allowed for efficient cutting of plant matter.[1] The solid, barrel-bodied creatures had a sprawling stance with a flexible backbone, which likely gave them a lizard-like appearance as they moved.[4] They were about 15 cm in length.[4]
Robertia is a member of the family Pylaecephalidae, which includes other small dicynodont therapsids with tusks such as Diictodon, Prosictodon, and Eosimops.[5]
Anomodonts and dicynodont subclade members were the most common species of the Permian and Triassic periods and were the first fossil vertebrates uncovered in the South African Karoo.[5] The discovery of these animals was especially important as they exhibited mammal-like traits outside of the Mammalia taxon.[5]
Keen fossil collector and amateur paleontologist A. G. Bain found the first anomodont in South Africa.[6] Noticing the two prominent canines, he assigned it to a new genus, “Bidental.”[6] Skull specimens were referred to Sir Richard Owen at the British Museum of Natural History, who placed them under the designation Dicynodon in the 1840s.[5][6] Comparable specimens, but without tusks were placed in a new genus Oudenodon.[6] As more of these mammal-like specimens were discovered during the early twentieth century, hundreds of species began to be described and amassed under the Dicynodon designation.[5][6] In 1954, Haughton and Brink alone uncovered 54 dicynodont genera in the Karoo Basin and characterized 111 species under the single genus Dicynodon.[7] Poor extraction and preparation of the Dicynodon type fossils and the minute differences that were used to distinguish its species contributed to the problem.[5] At this point, taxa were described through dorsal or lateral sketches of the skull, suture patterns, proportions of the skull, and notation of the presence or absence of teeth and tusks.[7] Further studies examining the lower jaw, postcanine teeth,[3] and other characteristics have reduced the large amount of dicynodont taxa into fewer, more valid genera.[7] The new group Pylaecephalinae (later Pylaecephalidae), within which Robertia lies, was established in 1934.[5] Species of this family contains those of Diictodon and its closest relatives, having a characteristic intertemporal region and pineal foramen located in the pre-parietal.[5]
Reexamining over a hundred skulls in the South African Museum designated Dicynodon jouberti, L.D. Boonstra separated out new taxa that fell outside the group.[5] Robertia was characterized by Boonstra in 1948.[3][6][8] The fossil specimens were discovered in the lower part of the Tapinocephalus Zone in the west part of the Beaufort Group.[6]
