The side wall of the braincase in cynodont therapsids, and a note on the homology of the mammalian promontorium

Abstract

The side wall of the cynodont braincase is not sufficiently well understood to form a sound basis for morphological or phylogenetic inference. This paper describes in detail the trigeminal region of a series of cynodonts from lateral and mesial aspects. Genera dealt with are Thrinaxodon, Trirachodon, Diademodon and Tritylodon. A reinterpretation of aspects of the braincase of the tritylodontid Bienotherium is presented. Attention is drawn to a fundamental dichotomy between herbivorous cynodonts and the carnivorous line leading to mammals. Homology between the cynodont parasphenoid wing and mammalian promontorium is demonstrated.