Species: A. bilineatus - A. blomhoffi - A. contortrix - A. piscivorus - A. taylori - A. tsushimaensis
Agkistrodon Palisot de Beauvois, 1799
Agkistrodon is a genus of venomous pit vipers found in North America from the United States south to northern Costa Rica. The name is derived from the Greek words ἄγκιστρον 'fishhook' (with the irregular transliteration gk rather than the usual nk) and ὁδοὐς (stem ὁδόντ-) 'tooth', and is likely a reference to the fangs. (The spelling Ankistrodon was formerly also used, but this is now reserved for an extinct genus of archosaurs.) Three species are currently recognized, all of them polytypic and closely related.
Members 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.
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.
Found 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.
All 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.
The members of this genus are all ovoviviparous.
It is assumed that the venom of all three species is not unlike that of A. contortrix, which contains thrombin-like 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.
||Mexico and Central America. On the Atlantic side it is found in Mexico in Tamaulipas, Nuevo León, possibly northern Veracruz and Chiapas (in the Middle Grijalva Valley). On the Yucatan Peninsula it occurs in Campeche, Yucatán, Quintana Roo and northern Belize. On the Pacific side it is found from southern Sonora in Mexico south through Guatemala, El Salvador, Honduras and Nicaragua to southwestern Costa Rica. On the Pacific side the distribution is almost continuous, while on the Atlantic side it is disjunct.
||The United States (Texas, Oklahoma, Kansas, Missouri, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, North Carolina, Tennessee, Kentucky, Virginia, West Virginia, Illinois, Indiana, Ohio, Iowa, Pennsylvania, Maryland, New Jersey, Delaware, New York, Connecticut, Massachusetts), Mexico (Chihuahua, Coahuila).
|The eastern United States from extreme southeastern Virginia, south through peninsular Florida and west to Arkansas, southeastern Kansas, eastern and southern Oklahoma and eastern and central Texas. A few records exist from along the Rio Grande River in Texas, but these are thought to represent isolated populations that possibly no longer exist.
The eastern United States from extreme southeastern Virginia, south through peninsular Florida and west to Arkansas, southeastern Kansas, eastern and southern Oklahoma and eastern and central Texas. A few records exist from along the Rio Grande River in Texas, but these are thought to represent isolated populations that possibly no longer exist.
Not including the nominate subspecies. T) Type species.
This genus was previously much larger and also included the following genera:
* Calloselasma - The Malayan pit viper found in Southeast Asia.
* Deinagkistrodon - The Hundred-pace viper found mostly in southern China.
* Gloydius - Moccasins found in Asia.
* Hypnale - Hump-nosed vipers found in India and Sri Lanka.
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* Jones JM. 1976. Variation of venom proteins in Agkistrodon snakes from North America. Copeia 1976(3): 558-562.
* Knight A, Densmore III LD, Real ED. 1992. Molecular systematics of the Agkistrodon complex, p. 49-70 In Campbell JA, Brodie Jr. ED. 1992. Biology of the Pitvipers. Texas: Selva. 467 pp. 17 plates. ISBN 0-9630537-0-1.
* Link HF. 1807. Beschreibung der naturalien-sammlung der Universität zu Rostock. Zweite abtheilung, pp. 51–100. Gebruckt bei Adlers Erben, Rostock.
* Palisot de Beauvois AMFJ. 1799. Memoir on Amphibia. Serpentes. Transactions of the American Philosophical Society 4: 362-381.
* Parkinson CL. 1999. Molecular systematics and biogeographical history of pitvipers as determined by mitochondrial ribosomal DNA sequences. Copeia 1999(3): 576-586.
* Parkinson CL, Moody SM, Ahlquist JE. 1997. Phylogenetic relationships of the "Agkistrodon complex" based on mitochondrial DNS data. P. 63-78 In Thorpe RS, Wüster W, Malhotra A. 1997. Venomous snakes: ecology, evolution and snakebite. Clarendon Press, Oxford.
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* Troost G. 1836. On a new genus of serpents, and two new species of the genus Heterodon, inhabiting Tennessee. Ann. Lyc. Nat. Hist., New York, 3: 174-190.
* Wagler JG. 1830. Natürliches System der Amphibien, mit vorangehender Classification der Säugthiere und Vögel. Ein Beitrag zur vergleichenden Zoologie. J.G. Cotta, München. 354 pp.