Deinocephalians of the U.S.S.R.

The deinocephalian pelvic girdle, of general pelycosaurian structure, is useful in systematic diagnosis. In primitive Russian deinocephalians, two contrasting pelvic patterns are recognized, one light, thin-walled, narrow, and of V-shaped cross-section, and the other massive, thick-walled, wide, and of U-shaped cross-section. The former is characteristic of two families of lightly- built, mobile land carnivores, the Eotitanosuchidae and the Brithopodidae. The Eotitanosuchidae are more primitive and pelycosaur-like, while the Brithopodidae show more variation, and specializations of large size, shallower acetabulum (related to mobility?), and re-enforcement of a weak pubic symphysis by additional processes. The massive type of pelvis characterizes large, heavily built herbivorous animals of the family Estemmenosuchidae. In general pelvic structure, the Estemmenosuchidae resemble the South African anteosaurs and tapinocephalians and the Russian tapinocephalians. In detail, however, they show a more primitive stage of evolution, overlaid by characteristic specializations which relate them more closely to the advanced Russian forms than to those of South Africa. Three new genera are erected, Biarmosaurus, fam. Eotitanosuchidae; Chthomaloporus, fam. Brithopodidae; and Molybdopygus, fam. Estemmenosuchidae. One specimen formerly referred to Deuterosaurus Yefremov 1954, and five formerly included in the type of Brithopus Yefremov 1954 are referred to Molybdopygus. The more primitive deinocephalians are from Yezhovo in the Ocher District, Perm Province, while more advanced forms are from Isheyevo, in Tataria, where-therocephalians and other South African elements are also found. It is therefore concluded that the Ochersk beds are older than those of Isheyevo and must be dated to zone I of Yefremov's system. — N. Hotton III.