Cylindrodontidae

Abstract

The skull of pre-Chadronian cylindrodonts is unknown, so this description is based on the known skulls of derived Chadronian species. In general shape, the skull is low and broad with a short, dorsoventrally deep rostrum (Fig. 7.1). The infraorbital foramen is small and unmodified by attachment of the masseter muscle (protrogomorphous). A low sagittal crest runs the length of the cranium. The orbital foramina are situated more anteriorly than in primitive ischyromyids. The bullae are inflated, ossified, and strongly attached to the skull. The mandible is deep with a strongly convex ventral margin. The scar for the masseter extends anteriorly only to below the posterior molars. The angle of the mandible is broad with a robust ventral ridge of the masseteric scar which gives the appearance that there is some lateral extension (considered “subhystricognathous” by Wood, 1980, 1984).