Geikia
Geikia is an extinct genus of dicynodont therapsids from the late Permian. The abundance and diversity of dicynodonts during this period, combined with incomplete or inadequately prepared specimens, have led to challenges in determining relationships within this taxon. Only two species, Geikia locusticeps and Geikia elginensis have been assigned to this genus. While this is the currently accepted classification, fossil record limitations have led to repeated debate on the genus assignments of these species. Description A high level of skull specialization was significant in the classification of Geikia. Maisch and Gebauer considered the squared off anterior snout tip and reduced exposure of squamosal in occiput to be characteristics exclusively expressed in Geikia. Prior to their analysis, Rowe described the generic diagnosis of Geikia as “dicynodonts having no tusk or postcanine teeth; highly vaulted palate; anterior palatal ridges of premaxilla reduced or absent; large palatine having rugose palatal surface; palatine having extensive contact with maxilla and premaxilla; length of interpterygoidal vacuity not less than half the length of the interpterygoidal fossa; interpterygoidal vacuity lying entirely within roof of interpterygoidal fossa; well developed maxillary caniniform process having pronounced lateral ridge; sharp occlusal margin of beak; sharp ridge or “keel” developed on central edge of maxilla behind caniniform process; septomaxilla having exposure on lateral surface of snout behind external nares; anterior surface of premaxilla flat, oriented vertically, and meeting lateral surface of premaxilla in abrupt “corner”; single, prominent preorbital protuberance". Discovery and naming This genus was established in 1893 following Edwin Tulley Newton’s discovery of a new dicynodont fossil, now known as G. elginensis, one of the Elgin Reptiles found near Elgin in Scotland. Newton discovered this specimen in conjunction with other new reptiles, but believed that G. elginensis’ characteristics were sufficiently unique to justify a new genus. The holotype is the only known occurrence, and is housed at the Institute of Geological Sciences in London. There have been two occurrences of the second species, G. locusticeps, both from the Ruhuhu Basin of Tanzania. Originally discovered by Friedrich von Huene in 1942, they are housed at the Institut und Museum für Geologie und Paläontologie der Universität Tübingen. The name Geikia was proposed by E.T. Newton, who investigated the G. elginensis holotype in 1892. This name was a dedication to Sir Archibald Geikie, the Director-General of the Geological Survey at the time. Specimens The only G. elginensis specimen is a natural mold of a nearly complete skull and mandible, associated left humerus, and an isolated metapodial or proximal phalanx. The G. locusticeps holotype is a skull lacking the tip of premaxilla, right quadrate, left temporal arch, and mandible. Two occurrences of this species exist in the fossil record. Analyses of G. elginensis and G. locusticeps indicate affinities to each other, but each also shares many characteristics with other taxa, including Pelanomodon, Oudenodon, and Ptychognathus (Lystrosaurus). The absence of some expected characteristics in G. elginensis could be explained under the assumption that it is subadult and, therefore, not fully developed. However, ontogenetic changes of both