The Interparietal in Kangaroo Rats

Abstract

A sample of 2,360 skulls representing 21 of the 22 recognized species of Dipodomys were examined for the presence and structure of the interparietal. The interparietal is basically formed from four ossification centers. These often fuse during the early stages of development. The median components are the equivalent of the interparietal of other animals while the antero-lateral components are possibly equivalent of the tabular bones of reptiles and primitive mammals. While examining a series of skulls of the Merriam kangaroo rat, (Dipodomys merriami) it was noted that the interparietal is variable in the number of bones composing it. Subsequently, 2360 skulls of 21 of the 22 recognized species of the genus Dipodomys (Hall and Kelson, 1959) were examined. In addition a series of 19 embryos of D. merri- ami were cleared in KOH and stained with Alizarin Red-S. The interparietal in Dipodomys, is bounded posteriorly and laterally by the supraoccipital and its ascending branches and anteriorly by the parietals (Fig. 1). In most species of this genus it is a shield-shaped structure, but may be only a narrow sliver wedged in between the ex- tremely developed auditory bullae of such species as D. deserti. As the animals become older, there is a tendency for the sutures be-