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Crotalus
:''Common names: rattlesnakes, rattlers.〔Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates (7th printing, 1985). 1105 pp. ISBN 0-8014-0463-0.〕''
''Crotalus'' is a genus of venomous pit vipers found only in the Americas from southern Canada to northern Argentina.〔 The name is derived from the Greek word ''krotalon'', which means "rattle" or "castanet", and refers to the rattle on the end of the tail which makes this group (genera ''Crotalus'' and ''Sistrurus'') so distinctive.〔Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.〕 Currently, 32 species are recognized.
==Description==
Members of this genus range in size from only 50–60 cm (''C. intermedius'', ''C. pricei''), to over 150 cm (''C. adamanteus'', ''C. atrox'').〔 In general, adult males are slightly larger than females. Compared to most snakes, they are heavy-bodied, although some African vipers are much thicker.〔Klauber LM. 1997. Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. First published in 1956, 1972. University of California Press, Berkeley. ISBN 0-520-21056-5.〕 Most forms are easily recognized by the characteristic rattle on the end of their tails, although a few island populations form exceptions to this rule: ''C. catalinensis'' has lost its rattle entirely, ''C. ruber lorenzoensis'' usually has no rattle, and both ''C. r. lucasensis'' and ''C. molossus estebanensis'' exhibit a tendency for rattle loss. The rattle may also be lacking in any species due to a congenital abnormality.〔
The rattle consists of a series of loosely interlocking hollow shells, each of which was at one point the scale covering the tip of the tail. In most other snakes, the tail tip, or terminal spine, is cone-shaped, hardly any thicker than the rest of the skin, and is shed along with it at each successive molt. In this case, however, the end-scale, or "button", is much thicker and shaped like a bulb, with one or two annular constrictions to prevent it from falling off. Before each molt, a new button will have developed inside the last one and before the skin is shed, the tip of new button shrinks, thereby loosening the shell of the previous one. This process continues so the succession of molts produces an appendage consisting of a number of interlocking segments that make an audible noise when vibrated. Since younger specimens may shed three or four times in a year, every time adding a new segment to the rattle, the number of segments bears no relation to the age of the snake. In theory, the rattle could become very long indeed, but in practice, the older segments tend to wear out and fall off. How quickly this happens depends on the snake's environment, but end segments tend to break off after the rattle becomes about six or seven segments long; it is uncommon to find specimens with as many as a dozen segments. In captive specimens, however, as many as 29 segments have been found.〔Parker HW, Grandison AGC. 1977. Snakes -- a natural history. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. ISBN 0-8014-1095-9 (cloth), ISBN 0-8014-9164-9 (paper).〕〔Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. ISBN 0-448-11856-4.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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