A faunivorous early sphenacodontian synapsid with a diastema

Abstract

Our knowledge on early sphenacodontian and edaphosaurid synapsids, the group that includes the origin of the mammalian lineage, largely arose from the Pennsylvanian Garnett locality in Kansas. A preliminary revision of the former “Haptodus” garnettensis found a greater diversity in the assigned material. The most striking deviation from the documented osteology is seen in a specimen comprising a lacrimal and associated maxilla. The diagnosis of this new form, Kenomagnathus scottae gen. et sp. nov., comprises a tall and shortened facial region, only two precanine teeth, and a distinct diastema. This is the oldest known diastema in synapsid evolution, and the first reported from a faunivorous member that lacks a precanine step, aside from Tetraceratops. This unique precanine morphology occurred independently from similar structures in Sphenacodontoidea. As for the edaphosaurid Gordodon, a specialized function in food processing is assumed for the diastema.