IV.—The Morphology and Relationships of a Complete Therocephalian Skeleton from the Cistecephalus Zone of South Africa

Abstract

SynopsisA description is given of a new genus of mammal-like reptile,Mirotenthes, of which a remarkably complete and well-preserved skeleton was collected in 1936 by Professor Camp of the University of California, from the late Permian deposits of the South African Karroo.Unlike the majority of Permian mammal-like reptiles,Mirotentheswas an agile form of small dimensions. Many of the skeletal characters exhibit a significant approach towards the mammalian threshold. The limb structure is very advanced and the digital formula is mammalian. The differentiation of ribs to form a definite rib-cage of mammalian type is particularly noteworthy and may indicate the presence in this genus of a mammalian respiratory mechanism.The systematic study of this complete skeleton does much to bridge the gap between the primitive basal groups of mammal-like reptiles and the advanced Triassic groups from which the mammals derive. It has been known for many years that small, fast-moving carnivorous forms were present in the late Permian fauna, but the evidence has been fragmentary. The complete skeleton described in this paper throws new light on these hitherto poorly known genera.