The oldest cynodont: New clues on the origin and early diversification of the Cynodontia

Abstract

Early mammaliaforms and their extinct relatives, nonmammaliaform cynodonts, have long been the focus of intense research in attempting to unravel how and when major changes toward mammalness occurred. The earliest well-known representatives of cynodonts are latest Late Permian in age. Here, we describe Charassognathus gracilis gen. et sp. nov., from the early Late Permian of South Africa, representing the oldest cynodont yet found. This specimen displays a notch on the dentary in the same location as the base of the masseteric fossa in the basal cynodonts Procynosuchus and Dvinia, and represents the first indication in theriodonts of an invasion of occlusal musculature onto the dentary. A phylogenetic analysis of seven therocephalians and ten non-mammaliaform cynodonts and equally weighted characters resulted in nine most parsimonious trees, the strict consensus of which shows a basal polytomy in cynodonts, including Charassognathus, Dvinia, Procynosuchus and a clade including the remaining cynodonts. The basal polytomy in the majority rule consensus tree is reduced, as Procynosuchus and Dvinia form a clade. One most parsimonious tree, from an analysis using implied weights, positions Charassognathus as the most basal cynodont. This result implies that the Cynodontia initially diversified in Permian Gondwana, in what is now southern Africa. © 2007 The Linnean Society of London.