Aplodontidae

Abstract

The zygomasseteric structure of aplodontids is the primitive protrogo-morphous condition (Fig. 9.1). The rostrum is dorsoventrally deep and the incisive foramina are small. The diastemata are short especially in aplodon-tines. In later species, the neurocranium is low and broad. There is never a single sagittal crest, but always broadly separated lyrate crests that unite at the midline of the cranium posteriorly or parallel parasagittal crests. Where known, all fossil aplodontids possess a short, laterally directed postorbital process. In the Recent genus Aplodontia, this is reduced to a small shelf above the orbit. The palate is broad and flat or slightly convex ventrally. There is a wide variety in the range of morphology of the cranial foramina from the most primitive to Recent genera. Primitively, the pterygoid flanges are long, the masticatory and buccinator foramina are united, and a stapedial foramen, an accessory foramen ovale, and a sphenofrontal foramen are present (Korth and Emry, 1991). In Aplodontia and more advanced fossil genera, the pterygoid area is much shortened (thus eliminating the accessory foramen ovale), the masticatory and buccinator foramina are separate, and the stapedial and sphenofrontal foramina are lost as a result of loss of the internal carotid artery. Much of this change in the skull is reflected in the increasing hypsodonty in the later aplodontines.