• The American alligator, which grows up to 19 feet (3.5 m) long, and up to 600 pounds (270 kg).
• The Chinese alligator, which grows to be about 6 feet long (1.8 m).

LOCOMOTION
Alligators have four legs. They swim very well, mainly using their tails to propel themselves through the water, and, to a lesser extent, using their webbed feet.

Alligators (like many reptiles) are plantigrade; they walk in a flat-footed manner. On land, they can run relatively fast, but only in short bursts.

The different types of crocodilians have different speeds; speed also varies depending upon the type of walk (belly crawl, high walk, gallop [only crocodiles], or swimming). Crocodiles are the fastest crocodilians on land; they can gallop at speeds up to 17 km per hour (Webb and Gans, 1982). Swimming, crocodiles can go about 10 km per hour. Doing a belly crawl walk, crocodiles can go 5-10 km per hour.

HABITAT AND RANGE
Alligators mostly live in fresh to brackish water, in swamps, marshes, canals, and lakes. The American alligator is found only in the southeastern part of the USA; the Chinese alligator is found in the lower Yangtze River basin in China.

ALLIGATOR BEHAVIOR
Alligators are usually solitary animals. They have a life span of up to about 30 to 35 years in the wild, and up to 50 years in captivity.

Alligators have a wide range of calls and vocalizations. These calls are used in mating, to define territory, as distress signals (babies grunt to alert the mother when in danger), etc.

ALLIGATOR REPRODUCTION
Alligators breed in the Spring (April to May). A month after the noisy mating rituals and coupling, the female lays up to 50 eggs in a large (three feet tall and six feet wide) nest she constructed of mud, leaves and twigs on dry ground. Alligators do not sit on their eggs; that would crush the eggs. The rotting vegetation in the nest warms the eggs. The temperature of the nest determines the sex of the hatchlings. If the eggs are incubated over 93 degrees Fahrenheit (34 degrees Celsius), the embryo develops as a male; temperatures below 86 degrees Fahrenheit (30 degrees Celsius) result in female embryos, between these temperatures, both sexes are produced. The female guards the nest from predators.

The eggs hatch in 2 months, producing hatchlings about 6 inches long (15 cm). The group of babies (called a pod) are protected by the female for about a year. Alligators are among the most nurturing of the reptiles.

DIET
Alligators are nocturnal and feed primarily at night. Younger alligators eat insects, shrimps, snails, small fish, tadpoles and frogs. Adult gators eat fish, birds, turtles, reptiles, and mammals. They swallow their prey whole. Their conical teeth are used for catching the prey, not tearing it apart. Alligators have about 80 teeth; when they are lost they regrow.

ALLIGATOR FOSSILS AND EVOLUTION
Crocodyloformes (the group encompassing crocodylians and other similar but extinct reptiles) evolved during the Triassic Period, about 245 million years ago. Crocodylians (a group which includes alligators, crocodiles, gharials or gavials, caiman) appeared during the Cretaceous period, about 80 million years ago, towards the end of the Mesozoic Era, the Age of Reptiles.

Deinosuchus (meaning "terrible crocodile") was the largest crocodylian, growing up to 50 feet (15 meters) long. It lived during the late Cretaceous period (about 85 to 66 million years ago). This carnivore lived on the shores of the large shallow sea (the Tethys Sea) that covered much of North America, eating fish and perhaps some dinosaurs. Very few Deinosuchus fossils have been found.

Crocodylian diversity peaked long ago; there are only 23 species alive now.

SOME ANCIENT, EXTINCT CROCODYLIANS

DEINOSUCHUS Deinosuchus (meaning "terrible crocodile") was the largest crocodylian (a reptile but not a dinosaur), growing up to 50 feet (15 meters) long. It lived during the late Cretaceous period (about 85 to 66 million years ago). This carnivore lived on the shores of the large shallow sea (the Tethys Sea) that covered much of North America, eating fish and perhaps some dinosaurs. Very few Deinosuchus fossils have been found.

GEOSAURUS (pronounced GEE-oh-SAWR-us) Geosaurus (meaning "rock lizard") was an early, aquatic crocodylian about 10 ft (3 m) long. This streamlined reptile had a long, pointed jaw with sharp teeth, four fleshy flippers (the rear flippers were considerably longer than the front flippers), and a long tail with a tail fin. Geosaurus was NOT a dinosaur, but did live side-by-side with ichthyosaurs from the late Jurassic period to the early Cretaceous period. Geosaurus fossils have been found in Europe (an especially nice specimen was found in southern Germany) and South Africa. Classification: Subclass Archosaur, Order Crocodylia, Suborder Thalattosuchia, Family Metriorhynchia, Genus Geosaurus.

LEIDYSUCHUS Leidysuchus (meaning "Leidy's crocodile;" Leidy was a paleontologist) was a long-snouted crocodile that lived during the late Cretaceous period. Fossils of this swamp-dwelling reptile have been found in North America.

PHOBOSUCHUS (pronounced FO-bow-SOOK-us) Phobosuchus (meaning "terrible crocodile") is one of the oldest alligator ancestors. This marine reptile was not a dinosaur, but a giant crocodylian. It lived in the seas during the Cretaceous period, about 70 million years ago, when many dinosaurs lived. This giant meat-eater was about 50 ft (15 m) long; its head was 6 feet (1.8 m) long and its teeth were 4 inches (10 cm) long. Phobosuchus may have eaten dinosaurs.

CLASSIFICATION
Alligators are reptiles and are closely related to dinosaurs and birds; they are all diapsids, and all have two opening on each side of the skull. Alligators are also Archosaurs (which have a single skull opening in front of the eyes), like the birds, dinosaurs, pterosaurs, and crocodiles. Alligators belong to the family Crocodilia, which include the alligators, caimans, crocodiles, and gharials.

• Vertebrates
  • Tetrapods (Amphibians, Reptiles, Turtles, Dinosaurs, Birds, Mammals, ...)
    • Diapsids (Reptiles, Dinosaurs, Birds)
      
      • Archosaurs (Dinosaurs, Birds, Crocodilians)
        
        • Crocodilians (23 species, including Alligators, Crocodiles, Caimans, Gharials)
          • Alligators
            • American Alligator (Alligator mississippiensis)
            • Chinese Alligator (Alligator sinensis)