This order has been founded by Professor Owen for the reception of a number of carnivorous Reptiles from deposits of Triassic or Permian age. The Reptiles in question show some singular Mammalian affinities, especially to the Beasts of Prey. The dentition is of the carnivorous type, the teeth being in three distinct sets - viz., incisors, canines, and molars, and the canines being large and pointed.
In Cynodraco, which may be regarded as the type of the group, the canines are not only of immense size, but are cornpressed in shape, and have the hinder trenchant border of the tooth minutely serrated, thus resembling the canines of the Sabre-toothed Tiger (Machairodus). The humerus is, further, furnished with a "supra-condyloid foramen " (similar to that of the humerus of Felidae and other carnivorous Mammals) for the protection of the median nerve and brachial artery on their way down the arm. Whilst Cynodraco is the type of the Theriodontia, Prof. Owen is of opinion that a number of other genera (such as Galesaurus, Cynochampsa, Lycosaurus, &c), principally of Triassic age, are likewise referable to the same order.
Fig. 319. - A, Front view of the skull of Lycosaurus, showing the dentition. B, Front view of the jaws of Cynodraco serridens, showing the incisor teeth. C, Side view of the jaws of Lycosaurus, showing the incisors and the laniariform canines; c Canines. (After Owen.)