The evolution of the dicynodont feeding system

The skull structure of dicynodonts may be regarded as a complex adaptation towards herbivorous feeding. The present work examines how and why this adaptation may have evolved. A cladogram of the dicynodonts is presented and from it a sequence of hypothetical ancestral forms is inferred. The jaw musculature of dicynodonts and other therapsids is described and in particular the early dicynodont Eodicynodon oosthuizeni is described in detail. This information is used to draw up a sequence of ancestral stages whose basic skull anatomy, jaw muscle organization and masticatory properties are described. Differences in masticatory properties between these stages are pinpointed and an explanation to account for the development of these differences is advanced. It is concluded that the changes in skull organization seen during the evolution of dicynodonts are consistent with the hypothesis that a propalinal jaw action was being improved by selection, and that this was required to permit dicynodonts to be efficient herbivores.