Zapodidae

Abstract

No skulls have been described of any North American Tertiary zapodids so the following discussion is based on the general morphology of Recent species (see Fig. 2.5A). Zapodids are small rodents. The cranium is inflated and the rostrum not especially elongated. The infraorbital foramen is enlarged for the passage of a branch of the masseter muscle (hystricomorphous) and there is a distinct accessory foramen medial to the infraorbital foramen for the passage of nerves and blood vessels. The zygomatic arch is reduced to a thin strip of bone. The markings for the attachment of the temporalis muscle are low and limited to the lateral margins of the parietal bones. On the palate the incisive foramina are enlarged, extending posteriorly to the level of at least the first molar. The auditory bullae are small and not inflated.