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The Boidae, commonly known as boas or boids, are a family of nonvenomous primarily found in the Americas, as well as Africa, Europe, Asia, and some Pacific islands. Boas include some of the world's largest snakes, with the green anaconda of South America being the heaviest and second-longest snake known; in general, adults are medium to large in size, with females usually larger than the males. Six Subfamily comprising 14-15 Genus and 54-67 species are currently recognized.
Both families share a number of primitive characteristics. Nearly all have a relatively rigid lower jaw with a coronoid element, as well as a vestigial pelvic girdle with hind limbs that are partially visible as a pair of spurs, one on either side of the Cloaca. In males, these anal spurs are larger and more conspicuous than in females. A long row of palatal teeth is present, and most species have a functional left lung that can be up to 75% as large as the right lung. Boidae at VMNH. Accessed 15 July 2008.
Boids are, however, distinguished from the pythons in that none has postfrontal bones or premaxillary teeth, and that they give birth to live young. When labial pits are present, these are located between the scales as opposed to on them. Also, their geographical distributions are almost entirely mutually exclusive. In the few areas where they do coexist, the tendency is for them to occupy different habitats.
Formerly, boas were said to be found in the New World and pythons in the Old World. While this is true of Boinae, other boid species are present in Africa, much of southern Eurasia, Madagascar, New Guinea, and the Solomon Islands, so this is not accurate. However, they seem more abundant in evolutionarily isolated areas. South America was isolated until a few million years ago, with a fauna that included and other distinctive . With the formation of the Panamanian land bridge to North America about three million years ago, boines have migrated north as Colubridae (and various Nearctic mammals) have migrated south, as part of the Great American Interchange.
Larger specimens usually eat animals about the size of a Cat, but larger food items are not unknown: the diet of the green anaconda ( Eunectes murinus) is known to include subadult . Prey is swallowed whole, and may take several days or even weeks to fully digest. Despite their intimidating size and muscular power, they are generally not dangerous to humans.
Contrary to popular belief, even the larger species do not crush their prey to death; in fact, prey is not even noticeably deformed before it is swallowed. The speed with which the coils are applied is impressive and the force they exert may be significant, but death is caused by suffocation, with the victim not being able to move its ribs to breathe while it is being constricted.
| Boinae | Gray, 1825 | 5 | 34 | true boas | Central America and South America and the West Indies |
| Calabariinae | Gray, 1858 | 1 | 1 | Calabar python | tropical West Africa and Central Africa |
| Candoia | Pyron, Burbink & Wiens, 2013 | 1 | 5 | bevel-nosed boas or keel-scaled boas | from Sulawesi through the Maluku Islands, New Guinea and Melanesia to Samoa and Tokelau |
| Erycinae | Bonaparte, 1831 | 3 | 18 | Old World sand boas | Southern and Southeastern Europe, Asia Minor, North, Central, West and East Africa, Arabia, Central and Southwest Asia, India, Sri Lanka, western Canada, the western United States, and northwestern Mexico |
| Sanziniinae | Romer, 1956 | 2 | 4 | Madagascan boas or Malagasy boas | Madagascar |
| Ungaliophiinae | McDowell, 1987 | 3 | neotropical dwarf boas | Central and South America from southern Mexico to Colombia | |
Almost all of the Boinae boids are frequently elevated to their own full families: Calabariidae/inae, Candoiidae/inae, Charinidae/inae, Erycidae/inae, Sanziniidae/inae, and Ungaliophiidae/inae. The taxonomy of boid snakes has been long debated, and ultimately the decision whether to assign a particular clade to a particular Linnaean rank (such as a superfamily, family, or subfamily) is arbitrary.
The subfamily Ungaliophiinae was formerly made up of four genera. Two of them ( Tropidophis and Trachyboa) are actually more closely related to the American pipe snake ( Anilius) than to the boas, and are now placed in the family Tropidophiidae within the superfamily Amerophidia. The other two genera ( Ungaliophis and Exiliboa) are the sister group of the Charina/ Lichanura clade within Boidae.
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