Permo-Jurassic Cynodonts: The Early Road to Mammalness

Abstract

The path to mammalness is well documented in the fossil record of Therapsida. Cynodontia is a group that includes living mammals and a series of stem fossil taxa that are individualized under the paraphyletic name of non-mammalian cynodonts. In this chapter I summarize the cynodont record of the late Permian, the post end-Permian extinction record and the remainder of the Triassic; and also examine two groups with strong morphological changes toward mammalness: Mammaliamorpha and Mammaliaformes (with the review of the last group restricted to the very basal forms documented in the Late Triassic-Early Jurassic). The final section of this contribution summarizes the advances in different areas of knowledge of cynodonts in the first 19 years of the 21st century. Among other topics considered are a tally of new species proposed, the discovery of new fossil sites with records of cynodonts, the phylogenetic hypotheses presented for different groups, and the tempo of cynodont evolution in light of recent changes in the geological temporal scale and the results of absolute dating.