CYNODONT DIVERSITY TRENDS IN THE TRIASSIC-EARLY JURASSIC

ABDALA, F.

Congreso; ixty-Ninth Annual Meeting Society of Vertebrate Paleontology and the Fifty-Seventh Symposium of Vertebrate Palaeontology and Comparative Anatomy (SVPCA); 2009

Cynodonts are an important component of Mesozoic faunas, and, in the Triassic, are frequently the most abundant group. Non-mammaliaform cynodonts are basal representatives of this group first documented in the Late Permian, and with their undoubted younger members from the Early Cretaceous. This paraphyletic group is composed of approximately 104 species/92 genera, 66 sp/59 gen of them represented in Gondwana and 39 sp/33 gen in Laurasia. Of these, only three taxa, the Late Permian Procynosuchus, the Middle Triassic Scalenodon and the Early Jurassic Pachygenelus are represented in deposits of both subcontinents. Results of an analysis of the diversity of cynodonts (nonmammaliaform cynodonts and basal mammaliaformes) during the Triassic and Early Jurassic indicate that they reach their maximum diversity of 46 genera during the Upper Triassic. Two peaks of diversity are recognized when analyzing the group at the level of temporal stage: the first during the Anisian with 21 genera and the second during the Norian, here considered as including the Rhaetian, with 28. The first peak is probably reflecting a large number of faunas of Anisian age including cynodonts (11, nine of them in Gondwana). The Norian peak is likely reflecting the number of localities (18, 15 of them in Laurasia), the long duration of the Norian stage (16.9 Ma) and an extensive record of isolated teeth representing several taxa, particularly from Europe.