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Mammals, Biodiversity of most bizarre elaboration of a general phenomenon found in the true moles, which have thousands of receptors arranged in a structure called the Eimer’s organ on the snout Cortical development of the brain is linked with the Eimer’s organ The Eimer’s organ assists moles in navigating and foraging in their tunnel networks The fourth family in Soricomorpha, the Soricidae family, contains the shrews, represented by 26 genera A very successful mammalian family, shrews are found on every continent except Australia and Antarctica Soricidae also boasts the world’s smallest living terrestrial mammal, the Etruscan shrew (Suncus etruscus), which weighs 1.8 g on average Erinaceomorphia The last of the new forms of Insectivora, the order Erinaceomorphia contains hedgehogs and gymnures The eight species of gymnures are found primarily in the rain forests of Southeast Asia, Gymnures are also called moonrats, and with good reason – they resemble rats much more than they their much closer relatives, the hedgehogs The 16 species of hedgehog are all well known for their spines, which are simply stiff hairs hollowed and supported by keratin, and their ability to roll into a ball as a defense mechanism Scandentia The five genera and 20 species of tree shrews (families Tupaiidae and Ptilocercidae) are the only extant members of the Scandentia The group is dispersed across the rain forests of southern Asia and Southeast Asia and has a relatively long fossil history (first found in the Eocene of Asia) Resembling a small squirrel, weighing 45–50 g, tree shrews have an elongated snout and a long, bushy tail Like true shrews, many species are known to consume insects; however, the few scientific studies that have been conducted on the family have found that fruit is often the dominant component of the diet Parental care is unusual, with the female giving birth to a small number of young (one to three) and hiding them in a nest In a pattern more common in antelopes, the female visits the young to nurse and then leaves them lying in Maturation is rapid, with independence from the mother at about a month and full sexual maturity at months Tree shrews are enigmatic in their phylogenetic affiliations They have variously been assigned to the primates, flying lemurs (Dermoptera), and rabbits (Lagomorpha), with both molecular and morphological analysis producing contradictory results Dermoptera Gliding, as opposed to true flying, is a mode of locomotion that has evolved independently in a number of mammalian orders The two living species of Dermoptera (family Cynocephalidae), also called colugos or flying lemurs, are a relictual group of gliders found today only in the forests of Southeast Asia Not closely related to lemurs, the dermopterans first appear in the fossil record in the Eocene of Thailand Throughout their evolutionary history, only two families of colugos have been described, one North American and the other Asian Affiliations of the order are unclear, with some paleontologists placing them as relatively close relatives to bats: they are not related to lemurs despite their common name The gliding membrane, or patagium, stretching over the 691 animal’s entire body, connecting along both sides of the tail to the legs, from legs to arms and from the arms to the neck, makes the animal look like a kite Despite their relatively large size, reaching a maximum size just under kg, the colugos are spectacular gliders, moving more than 100 m from tree to tree in the forest to reach the trees on which they feed The colugo diet is herbivorous but may include leaves, fruits, and flowers Chiroptera Bats represent the second most diverse order of mammals with 18 families, 202 genera, and 1050 species Two major suborders of bat have been distinguished, the Megachiroptera, also called fruit bats or flying foxes, and the Microchiroptera Bats come as small as 1.5 g with a wingspan of 15 cm (Craseonycteridae, Kitt’s hog-nosed bat) and as large as the flying foxes in the genus Teropus (Teropidae), which may weigh up to 1.5 kg and have wingspans of m The two suborders have long, independent evolutionary histories, although the very nature of their morphology, and in particular their fine, light bone structure, makes preservation unusual In contrast to modern diversity, sufficient fossil material has been found to describe just more than 30 genera The lack of fossil evidence has provoked repeated controversy and called into question whether bats are monophyletic or whether the fruit bats are actually more closely related to another group (primates are postulated because of shared evolution with megachiropterans of details of their neural pathways for vision) If this were the case, the remarkable flight structures would have to have evolved twice independently Molecular data show relatively unambiguously that the two bat groups are monophyletic Bats are the only mammals capable of true flight (as opposed to gliding) The wing is formed by a thin membrane that stretches across the arms, elongated fingers, and along the body, forming a diaphanous umbrella-like structure, or patagium Like all flying animals, bats need wings that are at once light but strong The wings are greatly reduced in weight with muscles pulled in close to the body and bones reduced in size land volume Torsional stress is reduced by simplification of joints The remarkable flying abilities of bats ensure a global distribution, with bats often the only mammal naturally occurring on remote islands Whereas birds monopolize diurnal aerial niches, bats are nocturnal specialists In some areas where birds and bats not co-occur, bats may become more diurnal, providing thin evidence of competitive exclusion Flying at night, visual acuity is of relatively little value; nonetheless, all but one species of Megachiroptera rely on vision to navigate In contrast, microchiropteran bats have evolved navigational tools that are independent of sight Using their larynxes, microchiropterans produce extremely high frequency sound that they emit through their nose or mouth The sound produced by bats is referred to as ultrasonic because it is above the range that humans can hear The ultrasound bounces off both potential prey and obstacles and is received back at the large, elaborated ears of the bat Because the bat navigates using the sound that bounces back, this form of navigation is called echolocation Despite their high specific diversity, patterns of reproduction (in the few species that have been studied) all are
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