Phylogeny

What is phylogeny you ask? Phylogeny is the evolutionary root of the studied behavior as it is seen in similar species and ancestors. It is most commonly traced by gene mapping and through use of the fossil record. Wikipedia: Phylogeny

Evolutionary Background

Although the bats are among the most diverse of mammals in the present day, there is onle a very sparse fossil record from which to derive a phylogenetic tree. This is because bats a light, small skeletons that are not well suited to preservation. many also live in tropical forests where conditions are unfavorable to the formation of fossils. Thus, little is known about the early phylogeny of bats.

Some mammal teeth discovered in France from the Paleocene show characteristics typical in bats and insectivores (others include shrews and moles), however, because these fossils are only teeth they do not speak to the rest of the individual. More complete bat fossils have been discovered from the Eocene in the Green River formation of Wyoming and in the Messel Shale of Germany. These fossils are essentially modern-looking chiropterans. By the Eocean bats had evolved their defining characteristics and begun to diversify. Some, like the image below, show specializations in the auditory region of the skull that suggest that the bat had begun to echolocate.

bat fossil

The oldest known megachiropteran is from the Oligocene and was discovered in Italy. This speciman and one from Africa make up the entire and remarkably sparse record of megachiropterans. The fossil record after the Oligocene shows a confinement in bats to the tropical regions of Africa, Asia and Australia, but this has now expanded (as seen below).

distribution

The current perspective on the evolution of echolocation in microbats has been shaped by recent molecular phylogenies, which suggest that many echolocating bads share a common ancestor with non-echolocating bats (Old-World fruit bats). One interpretation of these recent trees suggests that laryngeal echolocation (echolocating sounds are produced in the larynx) evolved in the ancestor of all extant bats. Following this, echolocation may have been lost by the Old World bats, only to evolve again in the form of tongue clicking.

Many more complex acoustic tricks like Doppler shift compensation, nasal emission of sound, and whispering echolocation each seems to have multiple convergent origins in bats.

Tree 1

Tree 2

Above: Current phylogenetic tree for modern mega and micro chiroptera, courtesy of tolweb.org.
The closest modern relative to bats are members of Dermoptera, shown below. Image below courtesy of Michigan Science Art.

relative