4. Tribe Cynodontia
Fig. 172. Skeleton of Cynognathus (Therapsida). After Gregory. One fourteenth natural size.
Especially characterized by a heterodont dentition, a secondary palate, reduced posterior mandibular bones, and two occipital condyles. Dentition composed of from three to five incisors, a canine, and seven to nine, rarely thirteen, molars, secodont or gomphognath or cuspidate. Temporal opening bounded by parietal and postorbital above, usually by squamosal and postorbital only below; frontals small, excluded from orbital margin by the union of the prefrontal and postorbital; postfrontals absent; parietals narrow; a small parietal foramen, but no preparietal bone; tabular large; quadrate small; stapes long, stout or slender; the pterygoids do not reach the quadrate; probably a small ectopterygoid; vomer large, unpaired. Coronoid large. A small acromion on scapula; scapula with reflected anterior border; no cleithrum. Fifth carpale unossified; phalangeal formula 2, 3, 3, 3, 3, so far as known. A thyroid foramen in pelvis. Feet imperfectly known, the digits short. Vertebrae amphicoelous; no dorsal intercentra. Twenty-eight presacrals, four sacrals.
Family Nythosauridae. Septomaxillae on face; molars less cuspidate; posterior mandibular bones less reduced.
Middle Triassic. Nythosaurus Owen, Ictidopsis Broom, Galesaurus Owen, Platycraniellus v. Hoepen, South Africa.
