Editing Boidae (section)

==Description==
Like the [[Pythonidae|python]]s, boas have elongated [[supratemporal]] bones. The [[quadrate bone]]s 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.<ref name="P&G77">Parker, H.W.; Grandison, A.G.C. 1977. ''Snakes – A Natural History''. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. {{ISBN|0-8014-1095-9}} (cloth), {{ISBN|0-8014-9164-9}} (paper).</ref>

[[File:Rudimentary hindlegs spurs in Boa constrictor snake.jpg|thumb|left|Cloaca region of a ''Boa constrictor'' with spurs (rudimentary hindlegs)]] 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 [[spur (zoology)|spurs]], one on either side of the [[Cloaca|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.<ref name="P&G77"/><ref>[http://www.curator.org/legacyvmnh/weboflife/kingdom/P_Chordata/ClassReptilia/O_Squamata/InfraSnakes/FBoidae/boidae.htm Boidae] {{webarchive|url=https://web.archive.org/web/20080518091427/http://www.curator.org/legacyvmnh/weboflife/kingdom/P_Chordata/ClassReptilia/O_Squamata/InfraSnakes/FBoidae/boidae.htm |date=2008-05-18 }} at [http://www.curator.org/ VMNH]. Accessed 15 July 2008.</ref>

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 [[Infrared sensing in snakes|labial pit]]s 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.<ref name="P&G77"/>
[[Image:Boavus idelmani.JPG|thumb|left|A fossil of ''[[Boavus]] idelmani'', an extinct species of boa]]

Formerly, boas were said to be found in the [[New World]] and pythons in the [[Old World]]. While this is true of [[Boinae|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 [[marsupial]]s and other distinctive [[mammal]]s. With the formation of the [[Isthmus of Panama|Panamanian land bridge]] to North America about three million years ago, boines have migrated north as [[Colubridae|colubrids]] (and various [[Nearctic]] mammals) have migrated south, as part of the [[Great American Interchange]].