A Middle Triassic cynodont fauna from Namibia and its implications for the biogeography of Gondwana

Abstract

ABSTRACT The upper Omingonde Formation of Namibia contains a diverse vertebrate fauna represented by amphibians, dicynodonts, archosaurs, therocephalians, and cynodonts, which is generally considered to be of Anisian age. Four cynodont taxa (Cynognathus, Diademodon, Trirachodon, and Titanogomphodon) are currently known from this fauna. Here we document four additional cynodonts, all of which were recovered from the highest levels of the formation: Luangwa, an indeterminate traversodontid, Aleodon, and Chiniquodon. These discoveries allow us to recognize the Omingonde Formation as preserving the most diverse fauna of Middle Triassic cynodonts in the world. Furthermore, we recognize that the formation is a biostratigraphic link among Middle Triassic faunas from South Africa, Tanzania, Zambia, Argentina, Brazil, and Antarctica. Aleodon is recorded here for the first time in Anisian faunas of southern Africa, and the unexpected record of Chiniquodon poses a biostratigraphic enigma because this taxon is known only from Ladinian–Carnian faunas of South America. We explore some possible scenarios related to the radiation of traversodontid cynodonts in Gondwana during the Anisian.