First record of a mastodonsaurid (Temnospondyli, Stereospondyli) from the Early Triassic Lystrosaurus Assemblage Zone (Karoo Basin) of South Africa

A partial mandible from near Venterstad is the first record of a mastodonsa urid from the Lystrosaurus Assemblage Zone. The paucity of mastodonsaurids in this biozone is unusual because of the local abundance of other temnospo ndyls, the abundance of mastodonsaurids in the overlying Cynognathus Assemb lage Zone, and the presence of mastodonsaurids in coeval faunas elsewhere i n Pangaea. This paucity does not reflect a preservational bias against larg e taxa, but may be due to palaeobiogeographic factors. The Lystrosaurus Ass emblage Zone mastodonsaurids were probably derived from the rich temnospond yl faunas of eastern Gondwana during the Early Triassic.