New species of the Miocene rodentCupidinimus(Heteromyidae) and some evolutionary relationships within the genus

Abstract

Geographic position strongly influenced evolution of species within Cupidinimus, a Miocene genus of pocket mice. One group of species evolved in the Californias–Nevada–Arizona region from about 16 to 5 million years ago (Barstovian through Hemphillian land-mammal ages), and includes C avawatzensis n. sp., C. halli (holotype illustrated), C tertius, C eurekensis, C quartus (holotype illustrated), C cuyamensis, and C bidahochiensis. High molar crowns and relatively frequent accessory cusps on P⁴ characterize this western group. A second group evolved farther to the northeast, in the Great Plains and north-central Rocky Mountains, from about 16 to 12 million years ago (Barstovian). This eastern group includes C. whitlocki n. sp., C. madisonensis, C. nebraskensis, and C. saskatchewanensis, which differ from Barstovian species to the southwest in possessing lower molar crowns and relatively infrequent accessory cusps on P⁴. A population from California previously referred to C. nebraskensis represents a separate, relatively primitive species, C lindsayi n. sp., which is not closely related to either of the major species groups. C kleinfelderi also seems to be of a slightly different lineage. C. boronensis, the only Hemingfordian species, is morphologically closest to the eastern species group. Traits shared by C whitlocki and C madisonensis (small P⁴ relative to molars) and by C. whitlocki and C. avawatzensis (similar size, enamel chevrons, cingulum on M²) may indicate gene flow within the Rockies and between the Rockies and California. Hypsodonty and extreme bilophodonty of cheek teeth, characters found even in the earliest Cupidinimus, were accentuated through time in both species groups by parallel evolution.