SYSTEMATICS OF THE DWARFED OREODONT SESPIA FROM THE LATE OLIGOCENE OF CALIFORNIA

Sespia californica is a dwarfed leptauchenin oreodont, first described by Chester Stock in 1930, that is common in early Arikareean (late Oligocene) deposits of southern California. Although the original material was very poor, hundreds of well-preserved new specimens from the Otay Formation of San Diego County allow a complete reassessment of the taxon. Statistical comparisons of this sample show that it is referable to the type species of Sespia californica from the Sespe Formation of Ventura County. However, comparison of the California specimens with the type material of Sespia nitida from the High Plains also shows they are indistinguishable, so Sespia californica is a junior synonym of Sespia nitida. Previous authors have alleged that Sespia showed sexual dimorphism, but we found no dimorphism in size, in the presence of "maxillary horns," or in other skeletal features, except for the size of the upper canines. Enlarged upper canines in males is typical of many other closely related living artiodactyl groups, such as tragulids, camels, and pigs. The appearance of Sespia is an important biostratigraphic marker, since it first occurs at 29.5 Ma within magnetic Chron C10r in both California and the High Plains.