Evolution and Classification of the Pocket Gophers of the Subfamily Geomyinae

by Robert J. Russell

The basitemporal fossa appears in late Pliocene geomyines and increases the attachment surface of the temporal muscles that powers the planing action important in utilizing woody and fibrous foods. The basitemporal fossa developed in only one of the modern lineages (tribe Geomyini), the same lineage in which grooved incisors evolved. Both features probably are adaptations for feeding on coarse food. The fossa is not greatly developed in either the ancestral tribe Dikkomyini or the modern tribe Thomomyini, although in some specimens a slight depression marks the site of the basitemporal fossa.

Fig. 1. Types of skulls in the subfamily Geomyinae. × 1.

A. and B. Generalized type of skull. Geomys bursarius lutescens, adult, male, No. 77955 KU, 10 mi. N Springview, Keya Paha Co., Nebraska.

A. Dorsal view of skull.
B. Ventral view of lower jaw.

C. and D. Dolichocephalic type of skull. Orthogeomys (Orthogeomys) grandis guerrerensis, adult, female, No. 39807 KU, 1/2 mi. E La Mira, 300 ft., Michoacán, México.

C. Dorsal view of skull.
D. Ventral view of lower jaw.

E. and F. Platycephalic type of skull. Pappogeomys (Cratogeomys) gymnurus tellus, adult, female, No. 33454 KU, 3 mi. W Tala, 4300 ft., Jalisco, México.