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Marsupial moles are a family (Notoryctidae) of cladotherian mammals of the order Notoryctemorphia. They are rare and poorly understood burrowing mammals of the deserts of Western Australia, with an ancestry going back 20 million years or so. Once classified as monotremes, they are now thought to be marsupials. Their precise classification was for long a matter for argument, but there are considered to be only two extant species:〔 * ''Notoryctes typhlops'' (southern marsupial mole, known as the ''itjaritjari'' by the Pitjantjatjara and Yankunytjatjara people in Central Australia). * ''Notoryctes caurinus'' (northern marsupial mole, also known as the ''kakarratul'') The two species are so similar to one another that they cannot be reliably told apart in the field. Marsupial moles spend most of their time underground, coming to the surface only occasionally, probably mostly after rains. They are blind, their eyes having become reduced to vestigial lenses under the skin, and they have no external ears, just a pair of tiny holes hidden under thick hair. It is debated whether or not marsupial moles dig permanent burrows or simply fill their tunnels in behind them as they move. ==Characteristics== The head is cone-shaped, with a leathery shield over the muzzle, the body is tubular, and the tail is a short, bald stub. They are between 12 and 16 cm long, weigh 40 to 60 grams, and are uniformly covered in fairly short, very fine pale cream to white hair with an iridescent golden sheen. Their pouch has evolved to face backwards so it does not fill with sand, and contains just two teats, so the animal cannot bear more than two young at a time. The limbs are very short, with reduced digits. The forefeet have two large, flat claws on the third and fourth digits, which are used to excavate soil in front of the animal. The hindfeet are flattened, and bear three small claws; these feet are used to push soil behind the animal as it digs. In a feature unique to this animal, the neck vertebrae are fused to give the head greater rigidity during digging. Marsupial moles provide a remarkable example of convergent evolution, with moles generally, and with the golden moles of Africa in particular. Although only related to other moles in that they are all mammals, the external similarity is an extraordinary reflection of the similar evolutionary paths they have followed. They are insectivorous, feeding primarily on beetle larvae and cossid caterpillars.〔 Their teeth are highly distinct from those of other mammals, with characteristics not seen in therians but present in more archaic mammal clades, shared specifically with dryolestoids. Their dental formula was thought to be similar to that of other marsupials - -, but more recent efforts show it to be distinct: . This formula is identical to the morphology seen in dryolestoids.〔On Dryolestid affinities () 〕 Marsupial moles are unique among mammals in their brain structure. Unlike therians and like monotremes, the olfactory bulb is located in front of the cerebrum as opposed to ventro-laterally displaced from midline, and they are larger than seen in monotremes. The neopallium is smaller than any other mammal, and it forms a dorsal cap lying on the pyriform lobe, and is not separated by any fissue, a condition seen also in monotremes but not therian mammals.〔Vaughan, T. A., Ryan, J. M. & Czaplewski, N. J. Mammalogy. 5th Edition. (Jones & Bartlett Learning, 2010).〕 Marsupial moles have a true cloaca, a feature only seen in mammals among monotremes and tenrecs, a fact which it was considered unusual.〔Gadow, H. On the systematic position of Notoryctes typhlops. Proc. Zool. Soc. London 1892, 361–370 (1892).〕 The urogenital sinus is much and longer than in monotremes, approaching the condition seen in therian mammals, but unlike with the latter it is undivided. The cloaca is devoid of skin glands and associated ducts, much like in monotremes. Like in monotremes, the penis is located inside the cloaca as opposed to externally like in therian mammals, while the testicles are internal and it lacks a scrotum. Only a pair of bulbo-urethral glandulae are present, much like in monotremes, unlike the presence of derived prostates and urethral glandules in therian mammals.〔Gadow, H. On the systematic position of Notoryctes typhlops. Proc. Zool. Soc. London 1892, 361–370 (1892).〕〔Riedelsheimer, B., Unterberger, P., Künzle, H. and U. Welsch. 2007. Histological study of the cloacal region and associated structures in the hedgehog tenrec Echinops telfairi. Mammalian Biology 72(6): 330-341.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Marsupial mole」の詳細全文を読む スポンサード リンク
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