Chiroptera

Bats are mammals in the order Chiroptera (pronounced /kaɪˈrɒptərə/). The forelimbs of all bats are developed as wings, making them the only mammals naturally capable of sustained flight (other mammals, such as flying squirrels, gliding possums and colugos, can only glide for limited distances). The word Chiroptera comes from the Greek words cheir (χειρ) "hand" and pteron (πτερον) "wing," as the structure of the open wing is very similar to an outspread human hand with a membrane (patagium) between the fingers that also stretches between hand and body.

A measure of the success of bats is their estimated total of about 1,100 species worldwide, accounting for about 20 percent of all mammal species. About 70 percent of bats are insectivores. Most of the rest are frugivores, with a few species being carnivorous. Bats are present throughout most of the world. Bats perform a vital ecological role by pollinating flowers, and also serve an important role in seed dispersal. Many tropical plants are entirely dependent on bats.

Bats range in size from Kitti's Hog-nosed Bat measuring 29–33 mm (1.14–1.30 in) in length and 2 g (0.07 oz) in mass, to the Giant golden-crowned flying fox which has a wing span of 1.5 m (4 ft 11 in) and weighs approximately 1.2 kg (3 lb).

Fossil bats

Since bats are terrestrial and light-boned, there are few fossilized remains. An Early Eocene bat, Onychonycteris finneyi, was found in the 52-million-year-old Green River Formation in South Dakota (US) in 2004. The new genus was placed in a new family when it was published in Nature, February 2008. It was clearly a flier, but the well-articulated skeleton showed that the cochlea of the inner ear lacked the developments which, in modern bats, provide echolocation capabilities; this indicates that flight in bats was developed before echolocation. The team realized Onychonycteris finneyi was different when they noticed that the species lacked the ear and throat features present not only in all living, echolocating bats today, but also in other ancient species known only from fossils.

The bats of 52.5 million years ago flew differently from the bats of today, and had a vastly different appearance. Onychonycteris had claws on all five of its fingers, whereas modern bats have - at most - claws for only two digits on each hand. It also had longer hind legs, and shorter forearms, similar to those of climbing mammals that hang under branches (such as sloths or gibbons). This palm-sized animal had broad, short wings, which suggests that it could not fly as fast or as far as later bat species. Instead of flapping its wings continuously while flying, Onychonycteris would likely have alternated flapping and gliding while airborne. These physical characteristics also suggest that this species did not fly as much as modern bats do, perhaps just flying from tree to tree and spending most of its waking day just climbing or hanging.

Another early Eocene fossil Icaronycteris index, was unearthed in 1960.

Classification and evolution

Bats are mammals. Though sometimes called "flying rodents", "flying rats," or even mistaken for insects and birds, bats are not, in fact, any of these things. There are two traditional suborders of bats:

• Megachiroptera (megabats)
• Microchiroptera (microbats/echolocating bats)

Despite the name, not all megabats are larger than microbats. The major distinction between the two suborders is based on other factors:

• Microbats use echolocation, whereas megabats do not (except for Rousettus and relatives).
• Microbats lack the claw at the second toe of the forelimb.
• The ears of microbats do not form a closed ring, but the edges are separated from each other at the base of the ear.
• Microbats lack underfur; they have only guard hairs or are naked.

Megabats eat fruit, nectar or pollen while microbats eat insects, blood (small quantities of the blood of animals), small mammals, fish and may also consume fruit, pollen or nectar. While megabats have a well-developed visual cortex and show good visual acuity, 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 into Megachiroptera and Microchiroptera reflects the predominant view which holds that these two groups of bats have evolved independently for a long time, from a common ancestor that was already capable of flight. This hypothesis recognizes the marked differences between microbats and megabats, while at the same time acknowledging the likelihood that flight has evolved only once in mammals. In addition, the majority of molecular biological evidence supports the point of view that bats form a monophyletic group.

More recently, researchers have proposed alternative views of chiropteran phylogeny (and classification), but more research is required to assess the merits of these proposals.

• Genetic evidence indicates that megabats should be placed within the four major lines of microbats, which originated during the early Eocene. This has resulted in a new classification, which includes two suborders. The suborder Yinpterochiroptera includes the Pteropodidae or megabat family as well as the Rhinolophidae, Megadermatidae, and Rhinopomatidae families. The Yangochiroptera includes all the remaining families of bats. Because these relationships combine echolocating and non-echolocating bats, it's unknown if the ancestor of bats possessed laryngeal echolocation (which the bats of Pteropodiae subsequently lost) or if this ability evolved twice.
• As an alternative to the Yinpterochiroptera/Yangochiroptera classification, some researchers use Pteropodiformes and Vespertilioniformes as the names of suborders of chiroptera. This nomenclature is said to have more long-term stability. Under this new proposed nomenclature, the suborder Pteropodiformes would be defined to include all extant bat families more closely related to the genus Pteropus than to the genus Vespertilio, while the suborder Vespertilioniformes would be defined to include all extant bat families more closely related to the genus Vespertilio than to the genus Pteropus.
• In the 1980s, it was hypothesized (based on morphological evidence) that Megachiroptera evolved flight separately from Microchiroptera. The so-called Flying primates theory proposed that when adaptations to flight are discounted in a cladistic analysis, the Megachiroptera are allied to primates by anatomical features that are not shared with Microchiroptera. For example, the brains of megabats show a number of advanced characteristics linking these animals to primates. Although recent genetic studies support the monophyly of bats, debate persists about the relative merits of DNA versus morphological evidence in settling this controversy.

Little fossil evidence exists about 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. The oldest known definite bat fossils, such as Icaronycteris, Archaeonycteris, Palaeochiropteryx and Hassianycteris, are from the early Eocene (52.5 million years ago), but they were already very similar to modern microbats. 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 similarities between Megachiroptera and these mammals. However, genetic studies have now placed bats in the superorder Laurasiatheria along with carnivorans, pangolins, odd-toed ungulates, even-toed ungulates, and cetaceans.

Below is the traditional classification of bats.

• Order Chiroptera
  • Suborder Megachiroptera (megabats)
    • Pteropodidae
  • Suborder Microchiroptera (microbats)
    • Superfamily Emballonuroidea
      • Emballonuridae (Sac-winged or Sheath-tailed bats)
    • Superfamily Molossoidea
      • Antrozoidae (Pallid bats)
      • Molossidae (Free-tailed bats)
    • Superfamily Nataloidea
      • Furipteridae (Smoky bats)
      • Myzopodidae (Sucker-footed bats)
      • Natalidae (Funnel-eared bats)
      • Thyropteridae (Disk-winged bats)
    • Superfamily Noctilionoidea
      • Mormoopidae (Ghost-faced or Moustached bats)
      • Mystacinidae (New Zealand short-tailed bats)
      • Noctilionidae (Bulldog bats or Fisherman bats)
      • Phyllostomidae (Leaf-nosed bats)
    • Superfamily Rhinolophoidea
      • Megadermatidae (False vampires)
      • Nycteridae (Hollow-faced or Slit-faced bats)
      • Rhinolophidae (Horseshoe bats)
    • Superfamily Rhinopomatoidea
      • Craseonycteridae (Bumblebee Bat or Kitti's Hog-nosed Bat)
      • Rhinopomatidae (Mouse-tailed bats)
    • Superfamily Vespertilionoidea
      • Vespertilionidae (Vesper bats or Evening bats)

Megabats are primarily fruit- or nectar-eating. They have probably evolved for some time in New Guinea without microbat concurrention. This has resulted in some smaller megabats of the genus Nyctimene becoming (partly) insectivorous to fill the vacant microbat ecological niche. Furthermore, there is some evidence that the fruit bat genus Pteralopex from the Solomon Islands, and its close relative Mirimiri from Fiji, have evolved to fill some niches that were open because there are no nonvolant (non-flying) mammals in those islands.

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