The Bat
Bats are unmistakable. No mammals other than bats have true wings and flight. Bat wings are modified forelimbs, much the same as bird wings, except in the case of bats the flight surface is covered with skin and supported by four fingers, while in birds the flight surface is provided mostly by feathers and is supported by the wrist and two digits. The flight membrane usually extends down the sides of the body and attaches to the hind legs. Bats also often have a tail membrane called a uropatagium. In order to accommodate powerful flight muscles, the thoracic region of bats is quite robust. In addition to providing power, a massive chest and shoulders maintains the centre of gravity between the wings, making flight more efficient. The opposite is true of the posterior end of the body, which is small relative to the chest and back. The hind limbs in particular are generally short and small, with sharp, curved claws that help bats cling to surfaces in their roost.
There are several obvious morphological features that distinguish the two suborders. Mega chiropterans rely on vision to orient in the dark of night, and thus have large, prominent eyes. All micro chiropterans rely heavily on echolocation, and not vision, and generally have small eyes. Instead most micro chiropterans have large, complex pinnae (external ears), including an enlarged tragus or antitragus. Mega bats have claws on the second digits supporting their wings (with one exception); this is never the case in micro bats. Micro bats often have dentition or cheek teeth whose morphology can easily be related to dilambdodont teeth; mega bats have simplified cheek teeth that are difficult to interpret. Perhaps the biggest functional difference between vision and echolocation is that vision is a passive mode of perception, while echolocation is an active mode of perception. Vision typically relies on external sources of light energy. Echolocation is quite different in that the energy provided is by the animals themselves. Because bats have tight control over what kinds of sound they produce, they can exhibit a high degree of control over what types of objects they can perceive. Echolocation calls vary among species, within species, and even within individuals. This variation in echolocation behaviour reflects variation in the habitats bats are using and the food for which they are searching. Bats can also use "passive echolocation", detecting and locating prey based on prey-generated sounds, such as frogs calling or the sound of a beetle walking across sand.
Bats live surprisingly long lives. Typically, mammalian lifespans roughly correlate with their body size: smaller mammals live short lives, whereas larger mammals live longer lives. Bats are the only group of mammals that does not conform to this relationship. Despite the fact that bats are generally small mammals, many bats can live over 30 years in the wild. Where data on longevity is available, lifespans in the wild are often recorded from 10 to 25 years. Typically, a given species will live at least 3.5 times longer than other mammals of similar size.