LATE TERTIARY BATS (MAMMALIA, CHIROPTERA) FROM THE SOUTHWESTERN UNITED-STATES

Rare scattered occurrences of microchiropteran fossils in six localities in Arizona, Nevada, and California spanning parts of the late Miocene and Pliocene (late Hemphillian and Blancan land mammal ages) consist of teeth and a humerus fragment belonging to the families Vespertilionidae and Molossidae. Important records include the following: (1) a bat near Eptesicus but much smaller than Eptesicus fuscus, from the Redington fauna, Quiburis Formation, Arizona (late Hemphillian, ca. 5.9 Ma). (2) Lasiurus cf. L. blossevillii from the Verde fauna, Verde Formation, Arizona (early Blancan, ca. 4.2 Ma). This represents the first fossil record of this species and in connection with an occurrence of L. borealis from Texas, provides evidence that L. blossevillii has possibly been distinct from L. borealis for 3.5 Ma. (3) Eumops perotis from McRae Wash, St. David Formation, Arizona (late Blancan). This is the first Tertiary record of this species and the oldest record of Eumops in North America. (4) A specimen previously reported as Simonycteris stocki from the Wolf Ranch fauna, St. David Formation, Arizona (late Blancan, ca. 2.5 Ma) is referred to Antrozous pallidus. (5) A Myotis sp. with a humerus smaller than that of extant Myotis californicus and teeth of Antrozous pallidus from the Horse Spring Formation, near Moapa, Clark County, Nevada, of indefinite age but probably Blancan or possibly late Hemphillian by faunal correlation based on other taxa in the same assemblage. (6) Eptesicus fuscus from the Old Woman Sandstone, western facies, California (late Blancan). These records give the impression that the chiropteran fauna of southwestern North America had an essentially modern aspect in the late Tertiary; however, the chiropteran record is still extremely poor, and other published records for the Southwest (including Simonycteris, Plionycteris, and Anzanycteris) indicate evolutionary radiation (and extinction) as late as the Pliocene, at least for the Vespertilionidae.