Cope described the first known fossil geomyids in 1878, and published an excellent review of the two genera, Pleurolicus and Entoptycus, in 1884 (pp. 855-870, pl. 64, figs. 1-9). Both genera were recovered from the John Day Miocene deposits of Oregon. Cope did not propose a new systematic arrangement of these geomyids, but referred them to the family Saccomyidae and mentioned that the Saccomyidae was equivalent to the family Geomyidae of Alston. Winge, in 1887, followed Cope in referring Pleurolicus and Entoptycus to the Saccomyidae along with the living genera Thomomys and Geomys. Miller and Gidley (1918), in their synopsis of the supergeneric groups of rodents, proposed a new subfamily, Entoptychinae, to include the divergent Miocene pocket gophers. Miller and Gidley also revived the old subfamily Geomyinae of Baird (1858), but restricted its application to the modern pocket gophers and their immediate ancestors. In 1936, A. E. Wood revised the taxa of the subfamily Entoptychinae, and described the first Miocene genus, Dikkomys, of the Geomyinae. He followed the supergeneric classification of Miller and Gidley (1918).
The recent classifications of Simpson (1945) and Wood (1955) have combined the classifications of Merriam (1895) and Wood (1936). Wood (1955) brought up to date the list of genera, including those that were described after the publication of Simpson's classification (1945). In [Table 1], the list of genera is principally from Simpson (1945) but generic names used by Wood (1955) are included. This is the currently accepted classification.
The new classification proposed in this paper (see [Table 1]) includes three tribes proposed as vertical units; they are intended to stress the phyletic trends in the known evolutionary sequences by placing immediate ancestors together with their descendants.
Pliogeomys is placed in the same tribe (Geomyini) as Zygogeomys, Geomys, Orthogeomys, and Pappogeomys. That tribe includes the most specialized Geomyinae. Zygogeomys, Geomys, Orthogeomys, and Pappogeomys are lineages resulting from a Pleistocene radiation in which all the lineages diverged from a common Pliocene ancestor. The radiation of the Geomyini was well under way by the close of the late Pliocene. Although Pliogeomys may not be the actual ancestor, it closely resembles the primitive morphotype.
Table 1.—History of the classification of the Superfamily Geomyoidea
* Denotes extinct genera.
** Winge included in his family Saccomyidae the "group" Gymnoptychine and the contained genus Gymnoptychus Cope, 1873, which genus currently is placed in the family Eomyidae. The type of Gymnoptychus Cope, 1873, is synonymous with Ischyromys Leidy, 1856, and the valid name for the genus is Adjidaumo Hay, 1899.