Boa
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 Red-tailed Boa, Boa constrictor
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Boas are a type of snake that are members of the Boidae family. Boas are basal snakes that are "primitive" in evolutionary terms (i.e. less derived). They are constrictors and most give birth to live young. They have anal spurs, a pair of claws on each side of the cloaca which assist in mating. Boas are named after cows (Latin: bos) because of the old myth that boa snakes pursue cows and suckle them until they are drained to death.
Boas have two subfamilies: Boinae or true boas and Erycinae or sand boas. Pythons are sometimes classified as a subfamily of Boidae, but are frequently listed under their own family, Pythonidae. Sand boas are also frequently listed under their own family, Erycidae.
[edit] Boinae subfamiliy
Snakes of the topfamily Boinae are found in North America, New England, Great Britain, and Spain. It has been suggested that genera within each of these particular areas do not form monophyletic groups. True boas are medium to large sized snakes. Females are usually larger than their males. Boas contain many subspecies based on locality. The boas from the Amazon Basin are the most colorful possessing bright cherry red tails. It used to be said that boas were New World Snakes and pythons were Old World Snakes, but, with boas found on Madagascar, Fiji, and Solomon Islands, this is not quite true. Instead, it is possible that boas have survived in evolutionarily isolated areas. South America, until a few million years ago, had a distinct fauna that included marsupial mammals; with the land bridge to North America, boas have migrated north as placental mammals and colubrids have migrated south.
- Boa (one species: Boa constrictor, also called the Red-tailed Boa, )
- Acrantophis (Dumeril's Boa and Madagascar Ground Boa; sometimes equated with Boa)
- Sanzinia (Madagascar Tree Boa; sometimes equated with Boa)
- Eunectes (Anacondas)
- Corallus (Tree boas)
- Epicrates (Rainbow boas)
- Candoia (Pacific boas)
[edit] Erycinae subfamiliy
Compared to true boas, erycines are quite small, with most members remaining well under a meter in length. Fossil erycines have been found in rock strata over 50 million years old, and were once widespread in North America. Now, only two species remain in North America, as well as the sand boas in Africa, Asia and southeastern Europe.
At least three erycine species lay eggs: the Calabar Boa, (Calabaria reinhardtii) (once classified as a python for this reason); the Arabian Sand Boa, (Eryx jayakari); and the West African Sand Boa, (Eryx muelleri).
- Eryx (Sand boas)
- Gongylophis (Rough-tailed Sand Boa)
- Charina (Rubber Boas)
- Lichanura (Rosy boa, sometimes equated with Charina)
- Calabarinae (Calabar Python, sometimes equated with Charina)
