Evolution

The earliest complete bat fossils come from the Eocene era, 49-53 million years ago. These animals were already capable of flight and echolocation. There is a general consensus that extant bat species are monophyletic. Bats are in the order Chiroptera within the superordinal group Laurasiatheria, which includes carnivoes, whales, and anteaters. Although it was previously believed that bats are a sister group with flying lemurs, this theory has been disproved. One prevaling hypothesis speculates that the ancestral bat was arboreal, but diurnal and frugivorous. A nocturnal and insectivorous lifestyle could have evolved after birds began to exploit the previous niche (Speakman 2001).

Indiana Bat, courtesy of US Fish and Wildlife Service

Adapted from Jones and Teeling 2006

A molecular phylogeny of bat families. The colored text represents four different superfamilial groupings. Several interesting facts are apparent from the phylogeny. Many molecular studies agree that bats are monophyletic. Although they are typically still grouped as either Microchiroptera and Megachiroptera based on size and echolocation strategy, molecular evidence suggests a non-evolutionary basis for these groupings. For example, the sophisticated echolocating Microchiropteran Horseshoe bats (family Rhinolophidae), and are most closely related to non-echolocating Megachiropterans (family Pteropodidae) (Jones and Teeling 2006). Instead of Microchiroptera and Megachiroptera, newer studies have suggested designations of Yinpterochiroptera (red and blue families) and Yangochiroptera (green, orange, and purple families).

Adapted from Jones and Teeling 2006

Bat families from each sub-order separated by echolocation call design. As described above, the current theory of bat evolution distinguishes the two sub-orders of Yinpterochiroptera and Yangochiroptera. Some types of calls, such as constant frequency, are found in both sub-orders while some, such as tongue clicks, are restricted to one. Environment, more so than evolutionary history, is thought to play a very strong role in echolocation call evolution.