FOSSIL BATS OF THE AMERICAS
Fossils from the Oligocene I-75 LF and the early Miocene Thomas Farm LF are the first Tertiary records of the Natalidae, establishing the presence of this family in Florida between ~18 and 30 Ma in what is now temperate North America (Morgan and Czaplewski 2003). A sample of more than 30 fossils from Thomas Farm, representing the upper and lower dentition, humerus, radius, and femur, was recently described as the new genus and species Primonatalus prattae (Morgan and Czaplewski, 2003). The proximal radius of a natalid from I-75 is the earliest record for this family, but the specimen is too incomplete for an identification below the family level. Late Pleistocene fossils of extant natalid species are known from the West Indies and Brazil (Czaplewski and Cartelle 1998; Morgan 2001). The current distribution of this family is limited to the Neotropics, from Mexico to Brazil and in the islands of the West Indies. The Natalidae attain their greatest species richness in the West Indies where all three genera and all six living species occur, including two endemic genera (Chilonatalus and Nyctiellus) and four endemic species (C. micropus, C. tumidifrons, Natalus major, and Nyctiellus lepidus). The diversity and endemism of natalids in the West Indies suggests this group reached the Antilles early in their evolutionary history. The other two species are both found on the Neotropical mainland. Natalus stramineus occurs from Mexico to Brazil and N. tumidirostris is restricted to northern South America and several offshore islands in the southern Caribbean Sea.
The Natalidae probably originated in tropical North America, as the earliest record of this family is now known to be from the early Oligocene (~30 Ma) of Florida. Presumably natalids survived in tropical Middle America between the Miocene and the late Pleistocene, but they have no fossil record during that time. Neither family has a Tertiary record in South America. Natalids are now found throughout Middle America and the West Indies, but their distribution is restricted in South America where they occur primarily in the northern half of the continent and are rare in the Amazon Basin (Koopman 1982). Based on their species richness and presence of several endemic genera and species, natalids appear to have reached the West Indies by overwater dispersal early in their history (Oligocene or Miocene). Their marginal distribution, lack of endemism, and absence of a Tertiary fossil record in South America suggests that natalids may not have arrived on that continent until after the Great American Biotic Interchange in the late Pliocene (~2.7 Ma).