An alligator has a wide, rounded snout; a crocodile has a narrow snout; when an alligator closes its mouth, its lower teeth are hidden; when a crocodile closes its mouth, large teeth stick out.

Alligators, crocodiles, caimans and gharials make up one group called crocodilians; the family Alligatoridae has eight species, and only two are usually called alligators; the Chinese alligator is the only other species of alligator; alligators are not lizards: scientists put lizards in a different order, Squamata.

Alligators are more closely related to birds and dinosaurs than to lizards, snakes and turtles; crocodilians and birds share a common ancestor that lived around 240 million years ago; the American alligator first appeared over 80 million years ago and has remained mostly unchanged since.

In 2014 scientists sequenced the genomes of the American alligator, the saltwater crocodile and the Indian gharial; crocodilian genomes change an order of magnitude more slowly than mammal genomes; one scientist thinks the slow change comes from the long time between generations in crocodilians; genomes showed that alligators declined in number throughout the Pleistocene epoch.

As of November 2026, the alligator is the largest reptile in the United States; adult alligators weigh from 91 to 360 kilograms, and the average is about 150 kilograms; adult alligator lengths range from 257 to 437 centimeters, and the average is about 350 centimeters; female alligators rarely grow longer than 10 feet, but males can grow much larger. As of November 2026, Florida's record alligator for length is a male of 14 feet 3 1/2 inches, from Lake Washington in Brevard County, and Florida's record alligator for weight is a male of 1,043 pounds, from Orange Lake in Alachua County.

A newly hatched alligator is about 6 to 8 inches (15 to 20 centimeters) long; young alligators grow about a foot a year; alligators are old enough to breed when they are about 6 feet (1.8 meters) long; as of November 2026, an alligator in the wild typically lives 20 to 30 years, and the longest recorded life of a wild alligator is 56 years. As of November 2026, the longest recorded life of a captive alligator is 73.1 years.

An alligator has upward-facing nostrils at the end of its snout, so it can breathe with the rest of its body under water; an alligator usually takes a breath of air every 20 or 30 minutes; an alligator hiding under water can slow its heart to just 2 or 3 beats per minute; in a field study, tagged alligators in Florida's Banana River Lagoon often made inactive dives lasting about 310 seconds, at a mean depth of 0.75 meters. In that field study, the tagged alligators' periodic submerged swimming averaged 0.31 meters per second.

Small sensory spots around an alligator's face and jaws feel pressure changes in the water; some touch sensors in alligator skin are tuned to vibrations of 20 to 35 hertz, which suits tiny water ripples; in 2002 a University of Maryland biologist found that alligators in a dark aquarium turned to face single drops of water. The sensory spots most heavily wired to nerves sit in the mouth near the teeth, which suggests they help an alligator tell what is in its jaws.

An alligator can respond to sounds in water from 100 to 2,000 hertz, and to sounds in air from 100 to 8,000 hertz.

An alligator eats fish, turtles, birds and small mammals; alligators hunt mostly at night; a 2011 diet study in Texas found that invertebrates made up 15.7 to 34.6 percent of alligator diets; an alligator uses its sharp teeth to seize and hold food, and swallows small food whole.

An alligator has about 80 teeth, all the same size, and they are replaced rapidly throughout its life; an alligator can go through 3,000 teeth in its lifetime; about 10 percent of wild alligator teeth are fractured during normal use before the teeth are shed.

The bite of a 12-foot, 665-pound American alligator was measured at 2,125 pounds of force; scientists measured bite forces in adults of all 23 living crocodilian species, including the American alligator; bite-force values from captive alligators can be used to model wild alligators when the values are matched to body mass.

Alligators live in fresh water, in slow rivers, swamps, marshes and lakes; American alligators live across the southeastern United States, from the northern coast of North Carolina to central Texas; the American alligator is the crocodilian with the northernmost range in the world; a female alligator usually stays in a small area, while a male can range over more than two square miles.

Alligators were hurt by market hunting and loss of habitat; the alligator was listed as an endangered species in 1967; in 1987 the U.S. Fish and Wildlife Service removed the alligator from the endangered species list; programs that raised young alligators and released them into former habitat helped the species recover. As of November 2026, the International Union for Conservation of Nature rates the alligator as a species of least concern, and the main threat to alligators today is the loss of wetland habitat.

Since 1988, Florida has surveyed alligators on areas called alligator management units; nightlight surveys are commonly used to check the status and trends of crocodilian populations; nightlight counts miss some animals, which makes it hard to read population trends from uncorrected data; in Everglades surveys, small alligators were harder to detect than larger ones, and detection fell as water got deeper. From 2001 to 2008, small and medium alligators declined in most Everglades study areas, while large ones rose or showed no clear trend; Florida's standard alligator survey, begun in 1974, found more alligators per kilometer of shoreline between 1974 and 1992; alligator surveys are generally not comparable from place to place because effort and methods differ.

An alligator nest is made of plants and is usually 7 to 10 feet (2.1 to 3 meters) across; a mother alligator builds the nest and lays about 20 to 50 eggs in it; the temperature of the nest decides whether a baby alligator is a male or a female: at 31 degrees Celsius or below, female alligators hatch; a scientist at UC Santa Cruz wants to learn the molecular basis of temperature-dependent sex determination in alligators. From an average clutch of 35 eggs, an estimated 4 alligators reach maturity; a mother alligator may carry her hatchlings to the water in her mouth.

Words to know

• genomes: full gene sets
• epoch: span of time
• hertz: vibrations per second
• invertebrates: animals without backbones
• fractured: cracked or broken