Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Viperidae

Snakes from this family, often referred to as vipers (although the common viper, or adder is but one species) are considered by most herpetologists to be the most highly evolved of all snakes. In particular, they have the most complex and effective means of venom delivery. Along with the elapids and a few of the colubrids vipers make up all of the venomous snake species. Snakes from this family are the cause of most snakebite fatalities in humans each year, more due to distribution and behaviour rather than great toxicity. The rattlesnakes (genus crotalus) are the most famous snakes in this family, but they are neither the largest (Bushmasters can reach a length of nearly 10 feet), or the most deadly.

Vipers have stocky bodies compared to other venomous snakes. They have large heads, which unlike the heads of colubrids or elapids are covered by small scales. Thus any venomous snake bite coming from a snake with small head scales must have come from a viper. Snakes of the genus Echis are responsible for most fatal viper bites in humans. Unlike other snakes vipers have hinged fangs, that are only errected when the snake strikes. This allows them to be longer than the fangs of elapids, and hence more suitable for delivering venom. The large heads of vipers contain venom glands that produce a venom that is usually primarliy haemotoxic. Viper bites thus tend to be more painful than those of elapids, and lead to greater local tissue damage. The haemotoxic venom also helps in the snakes' feeding, as it begins the process of digestion within the prey animal's body.

Snakes from this family can be found in most temperate or tropical regions of the world, but there are no vipers in Australia, Madagascar, New Zealand, or most of Oceania. Like other snakes they tend to prey on small mammals or reptiles. Most vipers are not built for speed, and thus capture their prey by means of ambushing techniques.

Subfamiles within the Viperidae family, and the genera classified within them:

Sources:
Snakes of the World: Mattison
www.curator.org
www.americazoo.com
www.ossm.edu

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