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A toothcomb (also tooth comb or dental comb) is a dental structure found in some mammals, comprising a group of front teeth arranged in a manner that facilitates grooming, similar to a hair comb. The toothcomb occurs in lemuriform primates (which includes lemurs and lorisoids), treeshrews, colugos, hyraxes, and some African antelopes. The structures evolved independently in different types of mammals through convergent evolution and vary both in dental composition and structure. In most mammals the comb is formed by a group of teeth with fine spaces between them. The toothcombs in most mammals include incisors only, while in lemuriform primates they include incisors and canine teeth that tilt forward at the front of the lower jaw, followed by a canine-shaped first premolar. The toothcombs of colugos and hyraxes take a different form with the individual incisors being serrated, providing multiple tines per tooth. The toothcomb is usually used for grooming. While licking the fur clean, the animal will run the toothcomb through the fur to comb it. Fine grooves or striations are usually cut into the teeth during grooming by the hair and may be seen on the sides of the teeth when viewed through a scanning electron microscope. The toothcomb is kept clean by either the tongue or, in the case of lemuriforms, the sublingua, a specialized "under-tongue". The toothcomb can have other functions, such as food procurement and bark gouging. Within lemuriforms, fork-marked lemurs and indriids have more robust toothcombs to support these secondary functions. In some lemurs, such as the aye-aye, the toothcomb has been lost completely and replaced with other specialized dentition. In lemuriform primates, the toothcomb has been used by scientists in the interpretation of the evolution of lemurs and their kin. They are thought to have evolved from early adapiform primates around the Eocene or earlier. One popular hypothesis is that they evolved from European adapids, but the fossil record suggests that they evolved from an older lineage that migrated to Africa during the Paleocene (66 to 55 mya) and might have evolved from early cercamoniines from Asia. Fossil primates such as ''Djebelemur'', '''Anchomomys' milleri'', and ''Plesiopithecus'' may have been their closest relatives. The lack of a distinct toothcomb in the fossil record prior to 40 mya has created a conflict with molecular clock studies that suggest an older divergence between lemurs and lorisoids, and the existence of a ghost lineage of lemuriform primates in Africa. == Homologous and analogous structures == The toothcomb, a special morphological arrangement of teeth in the anterior lower jaw, is best known in extant strepsirrhine primates, which include lemurs and lorisoid primates (collectively known as lemuriforms). This homologous structure is a diagnostic character that helps define this clade (related group) of primates. An analogous trait is found in the bald uakari (''Cacajao calvus''), a type of New World monkey. Toothcombs can also be found in colugos and treeshrews, both close relatives of primates; however, the structures are different and these are considered to examples of convergent evolution. Likewise, small- or medium-sized African antelopes, such as the impala (''Aepyceros melampus''), have a similar structure sometimes referred to as the "lateral dental grooming apparatus". Living and extinct hyraxes (hyracoids) also exhibit a toothcomb, although the number of tines in the comb vary throughout the fossil record. Dating to the Eocene epoch over 50 mya, ''Chriacus'' and ''Thryptacodon''—two types of arctocyonids (primitive placental mammals)—also possessed an independently evolved toothcomb. 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「toothcomb」の詳細全文を読む スポンサード リンク
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