The Primitive Cynodont Procynosuchus: Structure, Function and Evolution of the Postcranial Skeleton

An almost complete, acetic acid prepared skeleton of Procynosuchus delaharpeae Broom, an Upper Permian cynodont, is described. The axial skeleton is primitive in lacking the expanded costal plates, and accessory zygapophyses of later cynodonts. The mechanism of the shoulder joint is interpreted, and it indicates that no significant locomotory forces were generated by the forelimb. The hindlimb was capable of both a sprawling and an erect gait. Specialized horizontal zygapophyses in the lumbar region, and other features, show that proficient aquatic locomotion also occurred. As a representative of a stage in the origin of the Triassic cynodonts, Procynosuchus indicates that the dual-gait mechanism of the hindlimb was functionally intermediate between a primitive sprawling gait and the obligatory erect gait of the later cynodonts.