FOSSIL BATS OF THE AMERICAS
OLIGOCENE AND MIOCENE BATS FROM
PALEOKARST DEPOSITS IN FLORIDA
Fossils representing six families of bats, Emballonuridae, Mormoopidae, ?Phyllostomidae, Natalidae, Vespertilionidae, and Molossidae, are known from Oligocene and early Miocene (31-16.5 Ma) fossil deposits in peninsular Florida. The Emballonuridae, Mormoopidae, and Natalidae, all of which are now restricted to the tropics, were previously unknown from Tertiary deposits in North America. The Brooksville 2 Local Fauna (5 species of bats), I-75 Local Fauna (7 bats), and Thomas Farm Local Fauna (9 bats) have the richest Tertiary bat faunas in North America. Recent studies establish a well-constrained biochronology for Florida faunas representing the Whitneyan, Arikareean, and Hemingfordian North American land-mammal ages (NALMA), many of which are paleokarst deposits containing bat fossils. The Florida vertebrate faunas from these three NALMA that contain bats are: I-75 (Whitneyan, early Oligocene, 30-31 Ma); Brooksville 2 (late early Arikareean, late Oligocene, 26-28 Ma); White Springs and Live Oak/SB 1A (late early Arikareean, late Oligocene, 24-26 Ma); Buda (latest early Arikareean, latest Oligocene, 23-24 Ma); Thomas Farm and Seaboard (early Hemingfordian, early Miocene, 18-19 Ma); Brooks Sink (late Hemingfordian, late early Miocene, 17-18 Ma).
Since Florida first emerged above sea level about 30 million years ago, the highly soluble Paleogene marine limestones in the northern part of the peninsula have been acted upon by both chemical and physical erosional processes to develop one of the most extensive karst terrains in North America (Lane 1986). From a paleontological standpoint, the most significant aspect of the northern Florida karst geomorphic province is the abundance of Cenozoic terrestrial vertebrate deposits, numbering several hundred sites, that occur in caves, fissures, and sinkholes. Nowhere else in North America are paleokarst deposits of Cenozoic age found in such abundance. Commercial limestone mining operations in northern Florida have resulted in the discovery of most of the fossil deposits in paleokarst features. The oldest of these fossil sites is early Oligocene (~30 Ma) in age and they are found throughout the remainder of the Cenozoic, with the largest number in the late Pleistocene.
The presence of bat fossils in many of the karst deposits from northern peninsular Florida strongly indicates that some of the sites represent the remnants of former cave systems. The richest Tertiary bat faunas known from Florida, including I-75, Brooksville 2, Thomas Farm, and Inglis 1A (latest Blancan NALMA, latest Pliocene, 1.8-2.0 Ma), were derived from sediment-filled fissures or sinkholes in Paleogene limestones. These karst deposits often contain significant samples of small vertebrates, including frogs, salamanders, lizards, snakes, and birds, as well as marsupials, insectivores, bats, lagomorphs, and rodents. The only major drawback of these paleokarst deposits is that they consist of isolated pockets of sediment that cannot be directly correlated stratigraphically. However, the abundance of small mammals in these sites, as well as the presence of other groups of age-diagnostic mammals (carnivores, horses, artiodactyls), generally allows detailed biochronologic comparisons with faunas of similar age in western North America that have associated geochronologic data such as radioisotopic dates or paleomagnetic stratigraphy. In this they are similar to the fossiliferous fissure fillings developed within paleokarst in other continents. For example, in southern Europe, the Quercy phosphorites in France and the Herrlingen sites in Germany produce numerous fossil bats and other small mammals (Remy et al. 1987; Sigé and Legendre 1997; Ziegler 2000) , which are correlated biochronologically by consensus of European scientists (BiochroM97, 1997). In Australia, the richly fossiliferous Miocene and Pliocene deposits of Riversleigh, northwestern Queensland, also yield diverse bats as well as many other fossil vertebrates (Hand 1985; Hand 1990; Hand 1996; Hand 1997a; Hand 1997b; Hand 1997c; Hand 1998; Hand et al. 1998; Menu et al. 2002; Archer et al. 1991), but are difficult to correlate because of their isolation from more typical fluvio-lacustrine deposits.