The dentitions of the Tritheledontidae (therapsida: cynodontia)

Three previously described monospecific genera of ictidosaurians (Tritheledontidae) are recognized on the basis of their postcanine dentitions. The least specialized is Pachygenelus monus, Watson (1913), the complete dentition of which is described for the first time: five specimens are described and referred to this species. The postcanine teeth of Diarthrognathus broomi, Crompton (1958) are described for the first time; they are derivable from those of Pachygenelus though considerably more specialized. Tritheledon riconoi, Broom (1912), from which the family derives its name, consists of a single specimen containing upper postcanines only; these are not closely comparable with the uppers of the other two genera but bear a strong resemblance to the lower postcanines of Diarthrognathus. The family is closely implicated in the origin of mammals and the possibility of polyphyly in the origin of mammals is raised.