Alligatoridae
| Alligators and caimans
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 American alligator
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Alligator |
Alligatoridae is a family of large, semi-aquatic reptiles in the order Crocodilia, variously known by the common names of alligator and caiman, and characterized by a lizard-like appearance, armor-like skin, long tapering jaws, and the fourth enlarged tooth of the under jaw received into an internal pit formed for it within the upper jaw. This is in contrast to the similar large reptiles in the family Crocodylidae (crocodiles), which have the fourth enlarged tooth of the lower jaw received into an external notch. There are many extinct genera and species, but only about eight extant species, two of which are known as alligators and six of which are known as caimans.
Overview
Crocodilia, the order to which alligators and caimans belong, has a long history, appearing in the fossil record about 84 million years ago in the late Cretaceous period. Today, the extant species are placed into three families: Alligatoridae (alligators and caimans), Crocodylidae (crocodiles), and Gavialidae (gharials). All of these are characterized by a similar lizard-like form, large size, skin that is thick and armor-like, a long snout, tecondont dentition (teeth set in bony sockets like mammals), teeth replacement throughout their life (except very old age), and a flexible semi-erect (semi-sprawled) posture. Each can walk in low, sprawled "belly walk," or hold their legs more directly underneath them to perform the "high walk" (Britton 2001). The semi-erect posture makes it possible for some species to gallop on land if necessary (Britton 2001).
Alligatoridae includes two extant groups, the alligators and the caimans. One of the differences between members of Alligatoridae and the similar members of Crocodylidae, the crocodiles, is in the fact that upper jaw completely overlaps the narrower lower jaw, with the teeth of the lower jaw fitting into depressions in the upper jaw, and thus mostly hidden when the mouth is closed. In crocodiles, the teeth of the lower jaw fit along the mouth of the about equally wide upper jaw, with the upper teeth interlocking with the lower teeth when the mouth is closed and more visible. In particular, the difference is evident with respect to the enlarged fourth tooth of the lower jaw. In members of Alligatoridae, it is not visible, fitting into a pit within the upper jaw. In crocodiles, it fits into an external notch and is visible.
Another major difference that distinguishes extant alligators and caimans (family Alligatoridae) from crocodiles (family Crocodylidae) and from gharials (family Gavialidae) is in their tolerance of salinity. Crocodiles and gharials have functioning salt glands (modified salivary glands) that allow them to excrete excessive salt and thus be more tolerant of saline environments. Alligators and caimans have the same structures but they are non-functioning terms of salt excretion and thus have a lower tolerance to salinity.
Alligators also differ from crocodiles in having wider and shorter heads, with more obtuse snouts, lacking a jagged fringe (which appears on the hind legs and feet of the crocodile), and having the toes of the hind feet webbed not more than half way to the tips. They also differ perceptible from the two surviving species of gharial (Gavialis gangeticus and Tomistoma schlegelii) in that the gavialids have a much thinner snout.
True alligators
Alligators proper occur in the fluvial deposits of the age of the Upper Chalk in Europe, where they did not die out until the Pliocene age. The true alligators are now restricted to two species, A. mississippiensis in the southeastern United States, which can grow to 4.24 m (14 ft) and weigh 1000 lbs (454.5 kg)[1], with the record length of 5.81 m (19 ft 2 in), and the small A. sinensis in the Yangtze River, People's Republic of China, which grows to an average of 1.5 m (5 ft). Their name derives from the Spanish el lagarto, which means "the lizard".
Caimans
In Central and South America, the alligator family is represented by five species of the genus Caiman, which differs from the alligator by the absence of a bony septum between the nostrils, and the ventral armour is composed of overlapping bony scutes, each of which is formed of two parts united by a suture. Some authorities further divide this genus into three, splitting off the smooth-fronted caimans into a genus Paleosuchus and the Black Caiman into Melanosuchus. Caimans tend to be more agile and crocodile-like in their movements, and have longer, sharper teeth than alligators.[2]
C. crocodilus, the Spectacled Caiman, has the widest distribution, from southern Mexico to the northern half of Argentina, and grows to a modest size of about 2.2 meters. The largest is the near-threatened Melanosuchus niger, the Jacare-assu, Large, or Black Caiman of the Amazon. Black Caimans grow to 16.5 feet (5 meters) [3], with the largest recorded size 5.79 m (19 ft). The Black Caiman and American Alligator are the only members of the alligator family posing the same danger to humans as the larger species of the crocodile family.
Although the Caiman has not been studied in-depth, it has been discovered that their mating cycles (previously thought to be spontaneous or year-round) are linked to the rainfall cycles and the river levels in order to increase their offspring's chances of survival.
Taxonomy
- ORDER Crocodilia
- Family Alligatoridae
- Genus Leidyosuchus (extinct)
- Genus Deinosuchus (extinct)
- Subfamily Alligatorinae
- Genus Albertochampsa (extinct)
- Genus Chrysochampsa (extinct)
- Genus Hassiacosuchus (extinct)
- Genus Navahosuchus (extinct)
- Genus Ceratosuchus (extinct)
- Genus Allognathosuchus (extinct)
- Genus Hispanochampsa (extinct)
- Genus Arambourgia (extinct)
- Genus Procaimanoidea (extinct)
- Genus Wannaganosuchus (extinct)
- Genus Alligator
- Alligator prenasalis (extinct)
- Alligator mcgrewi (extinct)
- Alligator olseni (extinct)
- Chinese Alligator, Alligator sinensis
- Alligator mefferdi (extinct)
- American Alligator, Alligator mississippiensis
- Subfamily Caimaninae
- Genus Necrosuchus (extinct)
- Genus Eocaiman (extinct)
- Genus Paleosuchus
- Cuvier's Dwarf Caiman, Paleosuchus palpebrosus
- Smooth-fronted Caiman, Paleosuchus trigonatus
- Genus Purussaurus (extinct)
- Genus Mourasuchus (extinct)
- Genus Orthogenysuchus (extinct)
- Genus Caiman
- Yacare Caiman, Caiman yacare
- Spectacled Caiman, Caiman crocodilus
- Rio Apaporis Caiman, C. c. apaporiensis
- Brown Caiman, C. c. fuscus
- Caiman lutescans (extinct)
- Caiman sorontans[citation needed] (extinct) - Not reported in the literature, probably a 'nomen nudum'
- Broad-snouted Caiman, Caiman latirostris
- Genus Melanosuchus
- Melanosuchus fisheri (extinct)
- Black Caiman, Melanosuchus niger
- Family Alligatoridae
ReferencesISBN links support NWE through referral fees
- ↑ <http://www.eparks.org/marine_and_coastal/marine_wildlife/alligator.asp>
- ↑ Guggisberg, C.A.W. (1972). Crocodiles: Their Natural History, Folklore, and Conservation. ISBN 0715352725.
- ↑ <http://www.flmnh.ufl.edu/cnhc/cbd-faq-q2.htm>
- Britton, A. 2001. Locomotion. Crocodilian Biology Database. Retrieved January 16, 2008.
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