|Copyright: Zahoor Ahmed (zahoor_salmi)
|Date Taken: 2009-02-04|
|Camera: Canon 40D, 400f5.6 L|
|Exposure: f/5.6, 1/800 seconds|
|More Photo Info: [view]|
|Photo Version: Original Version|
|Date Submitted: 2010-09-30 5:51|
|[Note Guidelines] Photographer's Note|
|Bats are flying mammals in the order Chiroptera (pronounced /kaɪˈrɒptərə/). The forelimbs of bats are webbed and developed as 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, glide rather than fly, and 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. Chiroptera comes from two Greek words, cheir (χείρ) "hand" and pteron (πτερόν) "wing."|
There are about 1,100 bat species worldwide, which represent about twenty percent of all classified mammal species. About seventy percent of bats are insectivores. Most of the rest are frugivores, or fruit eaters. A few species feed from animals other than insects. Bats are present throughout most of the world and perform vital ecological roles such as pollinating flowers and dispersing fruit seeds. Many tropical plant species depend entirely on bats for the distribution of their seeds.
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).
Bats are mammals. Sometimes they are mistakenly called "flying rodents" or "flying rats", and they can also be mistaken for insects and birds. There are two suborders of bats:
Microchiroptera (microbats/echolocating bats)
Not all megabats are larger than microbats. The major distinctions between the two suborders are:
Microbats use echolocation: megabats do not with the exception of Rousettus and relatives.
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 a well-developed visual cortex 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 that was 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.
Researchers have proposed alternate views of chiropteran phylogeny and classification, but more research is needed.
Genetic evidence indicates that 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, 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 fifteen-base pair deletion in BRCA1 and a seven-base pair deletion in PLCB4 present in all Yangochiroptera and absent in all Yinpterochiroptera. The Chiropteran phylogeny based on molecular evidence is controversial because microbat paraphyly implies that one of two seemingly unlikely hypotheses occurred. The first suggests that laryngeal echolocation evolved twice in Chiroptera, once in Yangochiroptera and once in the rhinolophoids. The second proposes that 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.
Analyses of the sequence of the "vocalization" gene, FoxP2 was inconclusive of 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.
In addition to Yinpterochiroptera and Yangochiroptera, the names Pteropodiformes and Vespertilioniformes have also been proposed for these suborders. 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.
In the 1980s, a hypothesis based on morphological evidence was offered that stated that the Megachiroptera evolved flight separately from the Microchiroptera. The so-called flying primates theory proposed that when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features that are 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 support the monophyly of bats, debate continues as to the meaning of available genetic and morphological evidence.
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. The oldest known definitely identified bat fossils, such as Icaronycteris, Archaeonycteris, Palaeochiropteryx and Hassianycteris, are from the early Eocene period, 52.5 million years ago. These fossil bats 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 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.
The finger bones of bats are much more flexible than those of other mammals. One reason is that the cartilage in their fingers lacks calcium and other minerals nearer the tips, increasing their ability to bend without splintering. The cross-section of the finger bone is also flattened compared to the circular cross section that human finger bones have, and is very flexible. The skin on their wing membranes has more elasticity and so can stretch much more than other mammals.
The wings of bats are much thinner than those of birds, so bats can manoeuvre more quickly and more accurately than birds. It is also delicate, ripping easily. However the tissue of the bat's membrane is able to regrow, such that small tears can heal quickly. The surface of their wings is equipped with touch-sensitive receptors on small bumps called Merkel cells, found in most mammals including humans, similarly found on our finger tips. These sensitive areas are different in bats as each bump has a tiny hair in the center, making it even more sensitive and allowing the bat to detect and collect information about the air flowing over its wings, thereby providing feedback to the bat to change its shape of its wing to fly more efficiently. Some bats like the little brown bat can use this dexterious ability where it is able to drink in mid air. Other bats such as the flying fox or fruit bat gently skim the water's surface, then land nearby to lick water from their chest fur. An additional kind of receptor cell is found in the wing membrane of species that use their wings to catch prey. This receptor cell is sensitive to the stretching of the membrane. The cells are concentrated in areas of the membrane where insects hit the wings when the bats capture them.
The teeth of microbats resemble insectivorans. They are very sharp to bite through the hardened armor of insects or the skin of fruit.
Mammals have one-way valves in veins to prevent the blood from flowing backwards, but bats also have one-way valves in arteries.
One species of bat has the longest tongue of any mammal relative to its body size. This is beneficial to them in terms of pollination and feeding. Their long narrow tongues can reach deep into the long cup shape of some flowers. When their tongue retracts, it coils up inside their rib cage.
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