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 |
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