Abstract

A new small cynodont from subzone B of the Cynognathus Assemblage Zone (earliest Middle Triassic) of South Africa is described as Lumkuia fuzzi. It is represented by a nearly complete skull and lower jaw, a shoulder girdle and forelimb, and articulated dorsal and caudal vertebrae. It is placed in the eucynodont clade Probainognathia on the basis of four unequivocal synapomorphies, including absence of a parietal foramen and expanded plates on the ribs and a secondary palate extending posteriorly to the level of the orbit. Lumkuia is the oldest and most
primitive probainognathian represented by adequate material. A cladistic analysis strongly supports the monophyly of Cynodontia, Epicynodontia (a new taxon Galesaurus, Thrinaxodon, and including eucynodonts), and Eucvnodontia. The analysis also supports
the eucynodont clades Probainognathia and Cynognathia, and Gomphodontia as a subgroup of the latter. Within Probainognathia, a chiniquodontid clade and a tritheledontid + mammaliaform clade are well ported. Probainognathus is sister to the latter clade, but this node breaks down in trees two steps longer than the shortest tree. Tritylodontids are deeply nested within the traversodont gomphodonts, with "Scalenodon" hirschoni weakly supported as their sister taxon.