Bat

Bats are mammals of the order Chiroptera (/kaɪˈrɒptərə/; from the Greek χείρ - cheir, "hand" and πτερόν - pteron, "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, can only glide for short distances. Bats do not flap their entire forelimbs, as birds do, but instead flap their spread-out digits, which are very long and covered with a thin membrane or patagium.
Bats represent about 20% of all classified mammal species worldwide, with about 1,240 bat species divided into two suborders: the less specialized and largely fruit-eating megabats, or flying foxes, and the more highly specialized and echolocating microbats.About 70% of bats are insectivores. Most of the rest are frugivores, or fruit eaters. A few species, such as the fish-eating bat, feed from animals other than insects, with the vampire bats being hematophagous.
Bats are present throughout most of the world, performing vital ecological roles of pollinating flowers and dispersing fruit seeds. Many tropical plant species depend entirely on bats for the distribution of their seeds. Bats are important in eating insect pests, reducing the need for pesticides. The smallest bat is the Kitti's hog-nosed bat, measuring 29–34 mm (1.14–1.34 in) in length, 15 cm (5.91 in) across the wings and 2–2.6 g (0.07–0.09 oz) in mass. It is also arguably the smallest extant species of mammal, with the Etruscan shrew being the other contender. The largest species of bat are a few species of Pteropus and the giant golden-crowned flying fox with a weight up to 1.6 kg (4 lb) and wingspan up to 1.7 m

Bats are mammals. In many languages, the word for "bat" is cognate with the word for "mouse": for example, chauve-souris ("bald-mouse") in French, murciélago ("blind mouse") in Spanish, saguzahar ("old mouse") in Basque, летучая мышь ("flying mouse") in Russian, slijepi miš ("blind mouse") in Bosnian, nahkhiir ("leather mouse") in Estonian, vlermuis (winged mouse) in Afrikaans, from the Dutch word vleermuis. An older English name for bats is flittermice, which matches their name in other Germanic languages (for example German Fledermaus and Swedish fladdermus). Bats were formerly thought to be most closely related to flying lemurs, treeshrews, and primates, but recent molecular cladistics research indicates they actually belong to Laurasiatheria, a diverse group also containing Carnivora and Artiodactyla.

The two traditionally recognized suborders of bats are:

Megachiroptera (megabats)

Microchiroptera (microbats/echolocating bats)

Not all megabats are larger than microbats. The major distinctions between the two suborders are:

Microbats use echolocation; with the exception of Rousettus and its relatives, megabats do not.

Microbats lack the claw at the second toe of the forelimb.

The ears of microbats do not close to form a ring; the edges are separated from each other at the base of the ear.

Microbats lack underfur; they are either naked or have guard hairs.

Megabats eat fruit, nectar, or pollen, while most microbats eat insects; others may feed on the blood of animals, small mammals, fish, frogs, fruit, pollen, or nectar. Megabats have well-developed visual cortices and show good visual acuity, while microbats rely on echolocation for navigation and finding prey.

The phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision between Megachiroptera and Microchiroptera reflects the view that these groups of bats have evolved independently of each other for a long time, from a common ancestor already capable of flight. This hypothesis recognized differences between microbats and megabats and acknowledged that flight has only evolved once in mammals. Most molecular biological evidence supports the view that bats form a single or monophyletic group.[14]

Researchers have proposed alternative views of chiropteran phylogeny and classification, but more research is needed.

In the 1980s, a hypothesis based on morphological evidence was offered that stated the Megachiroptera evolved flight separately from the Microchiroptera. The so-called flying primates theory proposes that, when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features not shared with Microchiroptera. One example is that the brains of megabats show a number of advanced characteristics that link them to primates. Although recent genetic studies strongly support the monophyly of bats, debate continues as to the meaning of available genetic and morphological evidence.

Genetic evidence indicates megabats originated during the early Eocene and should be placed within the four major lines of microbats.

Consequently, two new suborders based on molecular data have been proposed. The new suborder Yinpterochiroptera includes the Pteropodidae or megabat family, as well as the Rhinolophidae, Hipposideridae, Craseonycteridae, Megadermatidae, and Rhinopomatidae families The new suborder Yangochiroptera includes all the remaining families of bats (all of which use laryngeal echolocation). These two new suborders are strongly supported by statistical tests. Teeling (2005) found 100% bootstrap support in all maximum likelihood analyses for the division of Chiroptera into these two modified suborders. This conclusion is further supported by a 15-base-pair deletion in BRCA1 and a seven-base-pair deletion in PLCB4 present in all Yangochiroptera and absent in all Yinpterochiroptera.[17] The chiropteran phylogeny based on molecular evidence is controversial because microbat paraphyly implies one of two seemingly unlikely hypotheses occurred. The first suggests laryngeal echolocation evolved twice in Chiroptera, once in Yangochiroptera and once in the rhinolophoids.[18][19] The second proposes laryngeal echolocation had a single origin in Chiroptera, was subsequently lost in the family Pteropodidae (all megabats), and later evolved as a system of tongue-clicking in the genus Rousettus.[20]

Common pipistrelle, Pipistrellus pipistrellus

Analyses of the sequence of the "vocalization" gene, FoxP2 was inconclusive as to whether laryngeal echolocation was secondarily lost in the pteropodids or independently gained in the echolocating lineages. However, analyses of the "hearing" gene, Prestin seemed to favor the independent gain in echolocating species rather than a secondary loss in the pteropodids.[22]

In addition to Yinpterochiroptera and Yangochiroptera, the names Pteropodiformes and Vespertilioniformes have also been proposed for these suborders.[23][24] Under this new proposed nomenclature, the suborder Pteropodiformes includes all extant bat families more closely related to the genus Pteropus than the genus Vespertilio, while the suborder Vespertilioniformes includes all extant bat families more closely related to the genus Vespertilio than to the genus Pteropus.

Little fossil evidence is available to help map the evolution of bats, since their small, delicate skeletons do not fossilize very well. However, a Late Cretaceous tooth from South America resembles that of an early microchiropteran bat. Most of the oldest known, definitely identified bat fossils were already very similar to modern microbats. These fossils, Icaronycteris, Archaeonycteris, Palaeochiropteryx and Hassianycteris, are from the early Eocene period, 52.5 million years ago. Archaeopteropus, formerly classified as the earliest known megachiropteran, is now classified as a microchiropteran.

Bats were formerly grouped in the superorder Archonta along with the treeshrews (Scandentia), colugos (Dermoptera), and the primates, because of the apparent similarities between Megachiroptera and such mammals. Genetic studies have now placed bats in the superorder Laurasiatheria, along with carnivorans, pangolins, odd-toed ungulates, even-toed ungulates, and cetaceans.