Post-Jurassic mammal-like reptile from the Palaeocene

Abstract

MAMMAL-LIKE reptiles of the Order Therapsida document the emergence of mammals from more primitive synapsids¹ and are of unique zoological and palaeontological interest on that account². Therapsids, first appearing in the Early Permian³, were thought to become extinct in the Middle Jurassic^4,5, soon after the Late Triassic origin of mammals⁶. Here, however, we report the discovery of a therapsid from the late Palaeocene, 100 million years younger⁷ than the youngest previous occurrence of the order. This discovery nearly doubles the stratigraphic range of therapsids and furnishes their first record from the Cenozoic. The documenting fossils, an incomplete dentary containing three teeth, and four isolated teeth from other, conspecific individuals (Fig. 1), are from the Paskapoo Formation, at Cochrane, Alberta, Canada, from beds yielding a diverse mammalian fauna of early Tiffanian age⁸. These specimens are catalogued in the collections of the University of Alberta Laboratory for Vertebrate Paleontology (UALVP) and provide the basis for a new taxon, as named and described below.