Meeting Abstract

P1.135  Jan. 4  A preliminary review of cimolestid systematics with comments on the genus Procerberus STRAUSS, Justin J.; San Diego State University dinosaurs@comcast.net

Cimolestids, Late Cretaceous mammals known primarily from western North America, are suspected to include the origin of Carnivora as well as other placentals. This hypothesized relation is based on their position biostratigraphically, within late Cretaceous (70-64 mya) sediments, as well as on the carnassial-like occlusion of their dentition. Current systematic relationships of cimolestids are based almost entirely on tooth morphology, and remain largely unresolved. One cimolestid in particular, Procerberus, is of especial interest because of its uncertain placement in relation to a number of other taxa. While much speculation has been made about the exact placement of Procerberus, little study of the numerous specimens collected has been done. It has been hypothesized that Procerberus is a descendant of Cimolestes based on the placement of accessory cusps on both the premolars and the molars. Preliminary morphological analyses weakly support this conclusion, which may call for a systematic revision of Cimolestes, as this clade would be paraphyletic in this instance. However, the molariformization of the premolars in Procerberus is also seen in leptictids, which has been used to suggest a relationship. The paracone and metacone of the premolars of Procerberus are of nearly equal size, which is almost identical to the state of these cusps in the leptictid Gypsonictops. In the premolars of Cimolestes, the metacone is significantly smaller than the paracone. A more thorough analysis of a greater number of morphological characters is being conducted to bring greater resolution to these systematic relationships. It is expected to show greater support for the hypothesis that Procerberus is a close relative and possible descendant of Cimolestes, with little direct relation to leptictids.