Mammalia of the Early Oligocene (Chadronian) Raben Ranch Local Fauna, northwest Nebraska

The Raben Ranch Local Fauna of northwestern Nebraska is the largest and most diverse Early Oligocene (Chadronian) microfauna re-covered from the High Plains. Within the microfauna is the largest accumulation of teeth referable to the Multituberculata yet recovered from rocks of Early Oligocene age. The age of the fauna is Middle Chadronian and, along with fossils from Flagstaff Rim in Wyoming, may represent the youngest known occurrence of the Allotheria. Forty-seven specimens referred to the genus Ectypodus are described, and comparisons are made with previously described teeth from the Chad-ronian of Wyoming and Saskatchewan. The data presented by the Raben Ranch sample indicate the presence of only one species of Ectypodus. Eight problematical teeth are also described and ques-tionably referred to the Multituberculata. In light of the geologic range extension of the Allotheria by the presence of teeth in Early Oligocene rocks, the theory of competitive inferiority is challenged as being th