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Agkistrodon
Agkistrodon is a genus of venomous pitvipers found in North America from the United States south to northern Costa Rica.[1] The name is derived from the Greek words ancistro, meaning "hook" and odon, which means "tooth", and is likely a reference to the fangs.[2] Three species are currently recognized,[3] all of them polytypic and closely related.[4] Additional recommended knowledge
DescriptionMembers of this genus have a number of features in common. All species have a relatively broad head with short fangs. A loreal scale is present, except in A. piscivorus. There are usually nine large symmetrical platelike scales on the crown of the head, but in all species these are often irregularly fragmented or have sutures, especially in A. bilineatus. All have a sharply defined canthus rostralis and a vertically elliptical pupil. There are 6-10 (usually 8) supralabial scales and 8-13 (usually 10-11) sublabials. The dorsal scales are mostly keeled and at midbody number 21-25 (usually 23), while A. piscivorus has 23-27 (usually 25). There are 127-157 ventral scales and 36-71 subcaudals. Of the latter, some may be divided. The anal scale is single. All have a color pattern of 10-20 dark crossbands on a lighter ground color, although sometimes the crossbands are staggered as half bands on either side of the body.[2] The phylogeny of the three species has long been controversial. Studies based on morphological (Gloyd & Conant, 1990) and venom characteristics (Jones, 1976) support the idea that A. bilineatus and A. contortrix are more closely related. However, an analysis of mitochondrial DNA was conducted by Knight et al. (1992), as well as more recent molecular studies (Parkinson et al., 1997, 1999) have concluded that A. bilineatus and A. piscivorus are sister taxa, with A. contortrix being a sister species to them both.[2] Geographic rangeFound in North America from the northeastern and central USA southward through peninsular Florida and southwestern Texas. In Central America on the Atlantic versant from Tamaulipas and Nuevo León southward to the Yucatan Peninsula, Belize and Guatemala. Along the Pacific coastal plane and lower foothills from Sonora south through Guatemala, El Salvador, Honduras and Nicaragua to northwestern Costa Rica.[1] BehaviorAll are semiaquatic to terrestrial and are often found near sources of water. However, A. contortrix and A. bilineatus are also found in dry habitats, often far from permanent streams or ponds.[2] ReproductionThe members of this genus are all viviparous.[2] VenomIt is assumed that the venom of all three species is not unlike that of A. contortrix, which contains thrombinlike enzymes that act upon the coagulant activity of the blood. A study of electrophoretic patterns of proteins in venoms among and within populations of A. contortrix and A. piscivorus showed that substantial variation exists (Jones, 1976), and there is no reason to believe that these differences do not correspond with variations in toxicity.[2] Species
*) Not including the nominate subspecies (typical form). TaxonomyThis genus was previously much larger and also included the following genera:[1]
See also
References
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Agkistrodon". A list of authors is available in Wikipedia. |