FOSSIL BATS OF THE AMERICAS
Bats, small mammals of the order Chiroptera, are a diverse group of over 1000 species living around the world. [see also - UMich animal diversity web] Bats capture the imagination with their sophisticated aerial flight maneuvers and use of echolocation (biosonar) for orientation and for food location and capture. Only a generation or two ago, bats were often feared for various misguided reasons, but in the early 21st century they have been better appreciated for their important ecological roles. We recognize their significance as natural controls on insect populations and as pollinators and dispersers of many kinds of flowering plants. In many areas bats now enjoy conservation efforts including protection of some caves that provide their nursery roosts or hibernacula. [see also - Bat Conservation International]
The fossil record of bats is poor when compared with that of most other kinds of mammals. This is probably because of their small size, typically low population densities, and habitat selection. Their bones and teeth are tiny and fragile, making them difficult to find and less likely to be preserved as fossils. Many kinds of bats roost in tree foliage, tree hollows, rock crevices, karst, or in caves. [see also - National Speleological Society] These situations do not lend themselves readily to burial and preservation of bones. By comparison, other small mammals such as rodents are far more common, have relatively robust bones, and often live in burrows where their bones are readily buried and preserved.
The bat fossil record is restricted to the Cenozoic era, with the oldest known bats occurring in early Eocene deposits in North America and Europe (Simmons and Geisler 1998). The phylogenetic ancestry of bats is debated by vertebrate paleontologists and biologists. Morphological studies of bats and their fossils tend to show that the ancestry of bats is shared with that of colugos (southeast Asian gliding mammals of the order Dermoptera), early primates, and tree shrews (order Scandentia). In contrast, recent molecular studies of extant bats seem to indicate that bats have their ancestry among that of the ferungulates, a clade which includes carnivorans, cetaceans, artiodactyls, and perissodactyls, or among that of the lipotyphlans, a clade which includes hedgehogs, moles, and shrews. Evolutionary relationships within the Chiroptera also are debated and are the subject of intensive research. [see also - Tree of Life] New technology such as computed tomography are being applied by researchers to studies of the morphology and osteology of extant and extinct bats. [see also - DigiMorph] [see also - Nancy Simmons web page] This research can provide new insights to bat evolutionary relationships as well as contributing to an understanding of biodiversity and biogeography.