Bat
Bats are mammals of the order Chiroptera (/kaɪˈrɒptərə/; from the Ancient Greek: χείρ - cheir, "hand" and Ancient Greek: 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 are the second largest order of mammals (after the rodents), representing 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 highly specialized and echolocating microbats. About 70% of bat species 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, or feeding on blood.
Bats are present throughout most of the world, with the exception of extremely cold regions. They perform the 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 economically important, as they consume 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 (fruit bats or flying foxes) and the giant golden-crowned flying fox with a weight up to 1.6 kg (4 lb) and wingspan up to 1.7 m (5 ft 7 in).
The Mexican free-tailed bat is the fastest flying animal in horizontal flight.
Classification and evolution:
Bats are placental mammals. Bats were formerly thought to have been most closely related to the flying lemurs, treeshrews, and primates,[12] but recent molecular cladistics research indicates that they actually belong to Laurasiatheria, a diverse group also containing Carnivora and Artiodactyla.[13][14]
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 the genus Rousettus, megabats do not.[15]
Microbats lack the claw at the second finger of the forelimb.[16][17]
The ears of microbats do not close to form a ring; the edges are separated from each other at the base of the ear.[17]
Microbats lack underfur; they are either naked or have guard hairs.[citation needed]
Megabats eat fruit, nectar, or pollen. Most microbats eat insects; others may feed on fruit, nectar, pollen, fish, frogs, small mammals, or the blood of animals. 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.[18]
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 primate hypothesis 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,[19] debate continues as to the meaning of available genetic and morphological evidence.[20]
Genetic evidence indicates that megabats originated during the early Eocene and should be placed within the four major lines of microbats.[21]
Consequently, two new suborders based on molecular data have been proposed. The new suborder of Yinpterochiroptera includes the Pteropodidae, or megabat family, as well as the families Rhinolophidae, Hipposideridae, Craseonycteridae, Megadermatidae, and Rhinopomatidae[22] The other new suborder, Yangochiroptera, includes all of 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.[22] Perhaps most convincingly, a phylogenomic study by Tsagkogeorga et al (2013) showed that the two new proposed suborders were supported by analyses of thousands of genes.[21]
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.[23][24] 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.[25]
Common pipistrelle, Pipistrellus pipistrellus
Analyses of the sequence of the "vocalization" gene, FoxP2, were inconclusive as to whether laryngeal echolocation was secondarily lost in the pteropodids or independently gained in the echolocating lineages.[26] However, analyses of the "hearing" gene, Prestin, seemed to favor the independent gain in echolocating species rather than a secondary loss in the pteropodids.[27]
In addition to Yinpterochiroptera and Yangochiroptera, the names Pteropodiformes and Vespertilioniformes have also been proposed for these suborders.[28][29] 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.[18] 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.[30] A recent study by Zhang et al. places Chiroptera as a sister taxon to the clade Perissodactyla (which includes horses and other odd-toed ungulates).[31] However, the first phylogenomic analysis of bats shows that they are not sisters to Perissodactyla, instead they are sisters to a larger group that includes ungulates and carnivores.[21]
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