On some Triassic cynodonts from Tanganyika

1 A collection of gomphodont cynodonts obtained from the Manda Beds (Middle Trias) of the Ruhuhu valley in Tanganyika has been prepared. Two new forms, Cricodon metabolus and Aleodon brachyrhamphus, have been described, the former from an imperfect skeleton and the latter from a skull. 2 The postcanine teeth of Trirachodon angustifrons Parrington have been shown to differ sufficiently from the South African species of that genus to merit transfer to a new genus Scalenodon. A growth series of this form consisting of nine upper jaws and six dentaries has been described together with some postcranial elements. 3 Two postcanine teeth in an isolated maxilla have been shown to resemble those of Gomphodontosuchus brasiliensis von Huene from the Rio do Rasto Series of Brazil, and similarly the postcanine teeth of Scalenodon angustifrons have been shown to resemble those of the Brazilian form Traversodon stahleckeri von Huene, also from the Rio do Rasto Series. It has been concluded that the Triassic cynodonts of the Ruhuhu valley compare more closely with those of the Brazilian Rio do Rasto Series than with those of South African deposits. 4 It has been shown that there is evidence that the incisors and canines of Scalenodon angustifrons are replaced at least twice and consequently the dental succession of this advanced cynodont cannot be considered as mammalian. The replacement of the incisors appears to be alternate or “distichic”. 5 It has been shown that the ninth upper postcanine teeth of Cricodon metabolus, which are of the shearing type, ere undergoing replacement by gomphodont teeth; that the ninth and tenth upper postcanines are apparently also being replaced in two specimens of Scalenodon angustifrons; and that the sixth upper postcanine of Diademodon sp. indet. is undergoing replacement. It is concluded that the use of the terms “premolar” and “molar” is unjustified in gomphodont cynodonts. No evidence has been found of replacement of posterior postcanine in any mandible. 6 The available evidence supports the conclusion of earlier workers that the localities from which the material was collected are of Middle Triassic age.