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Reptiles - American Alligator

Region: Americas

Class: Reptilia

Order: Crocodilia

Family: Alligatoridae

Genus: Alligator

Scientific Name: Alligator mississipiensis

Description: Males can measure up to 3.6 m, although a male of 3 m is rare today. Females are smaller, rarely more than 2.3 m. Adults are black or greyish black. The skin is covered with horny rectangular scales arranged in rows linked by tough skin. The back of the head is protected by heavy plates of bone which are enlarged horny scales with bony scutes underneath as is the belly. These are also found on the back and at the base of the tail. The two ribs on the first cervical vertebra (the atlas) diverge only a little (unlike those of the crocodile) and there are more occipital and nuchal scutes on the alligator. Occipitgal - hind region of the vertebrate cranium: nuchal - pertaining to the neck. Crocodilians are the sole surviving remnants of the once abundant ruling dinosaurs. Alligators have a four-chambered heart whereas all other reptiles and lower forms have a two or three chambered heart. A third eyelid - a transparent membrane, enables the alligator to see underwater. A valve in the throat closes to prevent water flowing down the windpipe when prey is caught underwater. This same valve allows the alligator to hold prey in its jaws at the surface and continue to breathe. In common with other crocodilians, alligators do not have a movable tongue. The tongue is fastened to the floor of the mouth. Contrary to popular Tarzan movies, the upper jaw extends stiffly from the skull, is not hinged and cannot move separately from he rest of the skull. The lower jaw is hinged and can move. Each jaw has about 40 teeth, set in sockets. New teeth grow throughout life, pushing out and replacing old ones. When the mouth is closed, the upper teeth lie outside the lower; the fourth tooth from the middle on either side of the jaw fits into a pit in the upper jaw and is not visible as in the crocodiles.

Distribution: Southeastern United States. Range restricted by cold winters to the north and dry lands to the west. From North Carolina south to Florida. Eastern Texas, Alabama, southern half of Georgia and very few remain in southern Arkansas. In South Carolina almost all the remaining alligators inhabit the coastal plains. The largest populations are in Florida and Louisiana.

Habitat: Swamps, rivers, ponds, canals and marshes.

Food: Young newly hatched alligators take small minnows, small crayfish and water insects. As they grow, they are able to catch larger prey such as leopard frogs, cricket frogs, tree frogs, large minnows and large crayfish. Adults eat "anything that moves" such as turtles, fish (a large number of gar), bull frogs, Norway rats, rice rats, marsh rabbits, muskrats, a few birds (ducks, herons, egrets) snakes (including the venomous cottonmouth), newly hatched alligators, blue crabs and crayfish. Occasionally alligators manage to pull a large mammal such as a deer or wild pig into the water where they can be dismembered and eaten. Alligators play an important role by keeping the populations of rodents, such as muskrats and coypu or nutria under control.

Skin/Color/Coat: There are bony nodules on the outer sides of the limbs. The belly is light coloured, much smoother than the back and is only sparsely ossified. The typical characteristic of the Mississippi alligator is the relatively long but very flat and broadly rounded snout. In the midline of the back there are generally eight longitudinal rows of large scutes. The keels of the two central longitudinal rows of scutes along the top of the tail run parallel to one another right up to the end and do not curve outwards. The eyes are close together above the plane of the head and so are the nostrils, allowing the alligator to lie with most of its body submerged in the water. Alligators have the nasal cavity longitudinally divided by a bony septum, visible because of the bump of the nose exhibits a clear longitudinal sub-division. The hind feet are webbed with three white claws which are evolutionary vestiges of an upright life on land before returning to the water.

Vocalization: Alligators are among the most vocal of reptiles. They make many distinct calls including coughs, chirps and bellows related to distress, threats, hatching and courtship.

Reproduction and Development: Mating takes place in April, May and June. Males (bulls) are heard roaring and spend a lot of time fighting with other males over mates. Females play a more active part than males in courtship and defence of the nest site. Females are attracted to the males by their roaring and bellowing and also by a musky secretion from the glands in the males' throat and cloaca. Mating usually takes place at night in the water, with the pair swimming round faster and faster and finally mating with jaws interlocked and the male's body arched over the female's. The female constructs a nest 2.4 x 3.6 m across and 0.9 m high, with mud and vegetation. The eggs, hard shelled, 18-80, are laid in a depression on top of this mound and covered with more mud and vegetation. This may take 2 or 3 days. The nest is guarded by the female, the eggs are incubated by the fermentation of vegetation rotting in the sun and rain. The average nest temperature is 28 degrees C. Incubation takes 8 to 10 weeks. When the young alligators are ready to hatch, they "peep" loudly. The female, upon hearing this signal will uncover the nest. The young escape from the egg by cutting through the shell with an "egg tooth" which forms on the tip of the snout. After hatching, this tooth disappears. There is also some evidence that females can open eggs or carry young to the water. Hatchlings are about 20 to 22 cm weigh about 50 to 80 gm and are brightly coloured, black and yellow. The young are black and have whitish markings. The white markings turn yellow as they grow. The belly of the hatchling is puffed out with the remains of the egg yolk. The young head for water immediately after hatching.

Adaptations: Mainly nocturnal. They are able to adjust to different conditions prevailing in their range. These ranges include rivers, creeks, sloughs, ponds, lakes, canals and marshes; both fresh and salt water. In Florida where drought can occur, sometimes the only water available is in "gator holes". These depressions are constructed by alligators and provide places where they and other aquatic birds and fish can congregate until the rains come. In other areas, alligators tunnel into the soft earth of river banks and retreat into these at times of drought and cold weather. Cold weather slows down the body activities. It becomes sluggish, stops eating and becomes dormant eventually. Alligators are able to live on fat stored in the tail at this time. The situation of eyes and nostrils above the plane of the head enables the alligator to see and breathe while most of its body remains submerged. It has a strong laterally compressed tail for propulsion through the water. Maternal behaviour during the incubation of eggs and the first few weeks of life provide a better chance of survival for offspring.

Threats: Man - in the early 1700's, alligators were numbered in the millions. By 1900, 2.5 million had been killed in Florida alone, with the same number killed in Louisiana and the rest of the southeastern USA. The slaughter increased from 1930 to 1940 with 1 to 2 million killed in Florida. This was repeated over the entire range. By 1969, alligators were only seen in refuges and protected parks. Hunters virtually wiped out large alligators and now were killing smaller ones. By the mid-60's: Louisiana less than 40,000 remained, Mississippi less than 3,000 remained, Alabama less than 6,000 remained. Although hunting had become illegal, poachers continued their slaughter even in the Everglades National Park. In 1969 the American Alligator was declared Endangered by the United States government. New York City, where most of the skins were processed, passed a law forbidding any trade in alligator skins. By March 1979, the American Alligator was removed from the Endangered Species List. At that time there were more than 1,000,000 alive in the wild. By 1980, controlled hunting was allowed. Man is still the alligators' greatest threat, should hunting and poaching ever be allowed on the former scale. Young alligators were sold for many years as pets, only to be disposed of when they outgrew their surroundings.

Status: Common

References: Bellairs, Angus. The Life of Reptiles. Vol. 2, 1969, Weidenfeld and Nicholson, London