Boidae

The Boidae, commonly known as boas or boids, are a family of nonvenomous snakes 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. Five subfamilies, comprising 12 genera and 49 species, are currently recognized.

The Old Tupi name for such snakes was mbói, which figures in the etymology of names such as ''jibóia'' and ''boitatá'' (the Brazilian name for the mythical giant anaconda).

Description

Like the pythons, boas have elongated supratemporal bones. The quadrate bones are also elongated, but not as much, while both are capable of moving freely so when they swing sideways to their maximum extent, the distance between the hinges of the lower jaw is greatly increased.Parker HW, Grandison AGC. 1977. Snakes – a natural history. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. (cloth), (paper).

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 vent. 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
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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 boine boas, 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 marsupials and other distinctive mammals. With the formation of the Panamanian land bridge to North America about three million years ago, boines have migrated north as colubrids (and various Nearctic mammals) have migrated south, as part of the Great American Interchange.

Distribution and habitat

Most species are found in North, Central, and South America, as well as the Caribbean, while a few are found in southeastern Europe and Asia Minor, Northern, Central and East Africa, Madagascar, the Arabian Peninsula, Central and southwestern Asia, India and Sri Lanka, the Moluccas, and New Guinea through to Melanesia and Samoa.

Feeding

Prey is killed by constriction; after an animal has been grasped to restrain it, a number of coils are hastily wrapped around it. Then, by applying and maintaining sufficient pressure, the snake prevents its prey from inhaling, so that it eventually succumbs to asphyxiation. Recently, the pressures produced during constriction have been suggested as the cause of cardiac arrest by interfering with blood flow, but this hypothesis has not yet been confirmed.

Larger specimens usually eat animals about the size of a house cat, but larger food items are not unknown: the diet of the common anaconda, ''Eunectes murinus'', is known to include subadult tapirs. 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.

Reproduction

Most species are ovoviviparous, with females giving birth to live young. This is in contrast to the pythons, which all lay eggs ( oviparous).

Subfamilies

Type genus = ''Boa'' – Gray, 1825

Taxonomy

Pythons were historically classified as a subfamily of Boidae (called Pythoninae), but it was later determined that they are not closely related to boas despite having superficial similarities.

Almost all of the non-boine boids are frequently elevated to their own full family: Calabariidae/inae, Candoiidae/inae, Erycidae/inae, Charininae, Ungaliophiidae/inae, Sanziniidae/inae, and Calabariidae/inae. The taxonomy of boid snakes has long been 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 these (''Tropidophis'' and ''Trachyboa'') are actually more closely related to red pipesnakes than to boas, and are now placed in the Tropidophiidae within the Amerophidia. The other two genera, ''Ungaliophis'' and ''Exiliboa'', are the sister group of the ''Charina- Lichanura'' clade, within Boidae.

See also

* List of boine species and subspecies
* List of erycine species and subspecies

References

* Kluge AG. 1991. Boine Snake Phylogeny and Research Cycles. Misc. Pub. Museum of Zoology, Univ. of Michigan No. 178
PDF
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University of Michigan Library
Accessed 8 July 2008.

External links

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Snake families
Taxa named by John Edward Gray
Extant Maastrichtian first appearances