The American alligator (Alligator mississippiensis), sometimes referred to as a common alligator or just gator, is a large crocodilian reptile native to the Southeastern United States. It is one of the two extant species in the genus Alligator, and is larger than the only other living alligator species, the Chinese alligator.
Adult male American alligators measure in length, and can weigh up to , with unverified sizes of up to and weights of making it the heaviest member of the family Alligatoridae, and the second longest one, after the black caiman. Females are smaller, measuring in length. The American alligator inhabits subtropical and tropical freshwater wetlands, such as marshes and cypress swamps, from southern Oklahoma and Texas to North Carolina.Virginia Living Museum. (2016, April 30). Herp highlight #1: American alligator. Retrieved April 08, 2021, from https://thevlm.org/herp-highlight-1-american-alligator/ It is distinguished from the sympatric American crocodile by its broader U-shaped snout, with overlapping jaws and darker coloration, and is less tolerant of saltwater but more tolerant of cooler climates than the American crocodile, which is found only in tropical and warm subtropical climates.
American alligators are apex predators and consume fish, amphibians, reptiles, birds, mammals, and other American alligators. Hatchlings feed mostly on invertebrates. They play an important role as ecosystem engineers in wetland ecosystems through the creation of alligator holes, which provide both wet and dry habitats for other organisms. Throughout the year (in particular during the breeding season), American alligators bellow to declare territory, and locate suitable mates. Male American alligators use infrasound to attract females. Eggs are laid in a nest of vegetation, sticks, leaves, and mud in a sheltered spot on land near water. Young are born with yellow bands around their bodies and are protected by their mother for up to one year. This species displays parental care, which is rare for most reptiles. Mothers protect their eggs during the incubation period, and move the hatchlings to the water using their mouths.Merchant, M., Savage, D., Cooper, A., Slaughter, M., Perkin, J. S., & Murray, C. M. (2018). Nest attendance patterns in the American alligator (Alligator mississippiensis). Copeia, 106(3), 421-426. American alligators exhibit parental care for up to 3 years post birth.
The conservation status of the American alligator is listed as Least Concern by the International Union for Conservation of Nature. Historically, hunting had decimated their population, and the American alligator was listed as an endangered species by the Endangered Species Act of 1973. Subsequent conservation efforts have allowed their numbers to increase and the species was removed from endangered status in 1987. The species is the official state reptile of three states: Florida, Louisiana, and Mississippi.
History and taxonomy The American alligator was first classified in 1801 by French zoologist François Marie Daudin as Crocodilus mississipiensis. In 1807, Georges Cuvier created the genus Alligator for it,Alligator Cuvier, 1807. ITIS.gov based on the English common name alligator (derived from Spanish word , "the lizard").
The American alligator and its closest living relative, the Chinese alligator, belong the subfamily Alligatorinae. Alligatorinae is the sister group to the caimans of Caimaninae, which together comprise the family Alligatoridae shown in this cladogram:
Evolution
Fossils identical to the American alligator are found throughout the Pleistocene, from 2.5 million to 11.7 thousand years ago. In 2016, a Late Miocene fossil skull of an alligator, dating to approximately seven or eight million years ago, was discovered in Marion County, Florida. Unlike the other extinct alligator species of the same genus, the fossil skull was virtually indistinguishable from that of the modern American alligator. This alligator and the American alligator are considered to be sister taxa, suggesting that the A. mississippiensis lineage has existed in North America for seven to eight million years. However in 2020, a study reconsiders that American alligators Late Miocene record, with the older fossils being reassigned to Alligator mefferdi and Alligator hailensis, and with American alligators evolving sometime during the Middle Pleistocene.
The alligator's full mitochondrial genome was sequenced in the 1990s, and it suggests the animal evolved at a rate similar to mammals and greater than birds and most cold-blooded vertebrates. However, the full genome, published in 2014, suggests that the alligator evolved much more slowly than mammals and birds.
Characteristics
Domestic American alligators range from long and slender to short and robust, possibly in response to variations in factors such as growth rate, diet, and climate.
Size The American alligator is a relatively large species of crocodilian. On average, it is the largest species in the family Alligatoridae, with only the black caiman being possibly larger.Thorbjarnarson, J. B. (2010). Black caiman Melanosuchus niger. Crocodiles. Status Survey and Conservation Action Plan, 29–39. Weight varies considerably depending on length, age, health, season, and available food sources. Similar to many other reptiles that range expansively into temperate zones, American alligators from the northern end of their range, such as southern Arkansas, Alabama, and northern North Carolina, tend to reach smaller sizes. Large adult American alligators tend to be relatively robust and bulky compared to other similar-length crocodilians; for example, captive males measuring were found to weigh , although captive specimens may outweigh wild specimens due to lack of hunting behavior and other stressors.
Large male American alligators reach an expected maximum size up to in length and weigh up to , while females reach an expected maximum of .American Alligators, American Alligator Pictures, American Alligator Facts – National Geographic. Animals.nationalgeographic.com.American alligator . Philadelphia Zoo. However, the largest free-ranging female had a total length of and weighed . On rare occasions, a large, old male may grow to an even greater length.Charles, S.; Ross, A. and Garnett, Stephen (1989) Crocodiles and Alligators. Checkmark Books. .
Largest During the 19th and 20th centuries, larger males reaching were reported. The largest reported individual size was a male killed in 1890 by Edward McIlhennyWoodward, A. R., White, J. H., & Linda, S. B. (1995). Maximum size of the alligator (Alligator mississippiensis). Journal of Herpetology, 507-513. on Marsh Island, Louisiana, and reportedly measured at in length, but no voucher specimen was available, since the American alligator was left on a muddy bank after having been measured due to having been too massive to relocate. If the size of this animal was correct, it would have weighed about . In Arkansas, a man killed an American alligator that was and . The largest American alligator ever killed in Florida was , as reported by the Everglades National Park, although this record is unverified.Everglades National Park Flora & Fauna Page. Everglades National ParkFlorida alligator . Floridaadventuring.com (March 2, 2016). Retrieved on 2016-09-07. The largest American alligator scientifically verified in Florida for the period from 1977 to 1993 was reportedly and weighed , although another specimen (size estimated from skull) may have measured . A specimen that was long and weighed is the largest American alligator killed in Alabama and has been declared the SCI world record in 2014.
Reported sizes Date Location Reported length Reported weight Reported girth Reported skull length Scientifically analyzed length Comments January 2, 1890 Lake Vermilion, Louisiana 584.2 cm not listed not listed not listed not listed Shot by Edward Avery McIlhenny. Body was too heavy to tow out of the mud. 1886 Avery Island, Louisiana 523.24 cm not listed not listed not listed not listed Captured alive by John Avery and died en route to the Smithsonian Institution after a sailor poured green paint on its back. March 1916 Marsh Island, Louisiana 561.34 cm not listed not listed not listed not listed Killed by Max Touchet, a game warden on Marsh Island following an attempted live capture. 1956 Lake Apopka, Florida 530.86 cm not listed not listed not listed not listed Estimated by Allan Woodward to have been 421.64 cm using head to length formula. November 11, 2010 St Johns River, Florida 435.61 cm 297 kg not listed not listed 435.61 cm August 23, 2012 Lake Talquin, Florida 426.72 cm not listed not listed 60.325 cm 426.72 cm August 16, 2014 Alabama River, Alabama 480 cm 458.8 kg not listed not listed 480 cm Biologists initially measured a length of 457 cm. Later after the head and hide had been removed a measurement of 480 cm was made, likely a result of the hide stretching. May 31, 2016 Palmetto, Florida 426.72 cm not listed not listed not listed not listed Estimated to be between 426.72 cm and 457.2 cm when spotted. September 26, 2020 Lake Merrisach, Arkansas 425.45 cm 362.874 kg not listed not listed not listed February 2, 2022 Lake Washington, Florida 401.32 cm 410.501 kg not listed not listed not listed Killed by Doug Borries of Dynamic Outdoors TV after alligator began eating livestock. August 29, 2023 Yazoo River, Mississippi 434.34 cm 364.00 kg 167.64 cm not listed 434.34 cm September 7, 2025 Ross Barnett Reservoir, Mississippi 426.72 cm 272 to 317 kilograms not listed not listed 397.50 cm
Average American alligators do not normally reach such extreme sizes. In mature males, most specimens grow up to about in length, and weigh up to , while in females, the mature size is normally around , with a body weight up to . In Newnans Lake, Florida, adult males averaged in weight and in length, while adult females averaged and measured . In Lake Griffin State Park, Florida, adults weighed on average . Weight at sexual maturity per one study was stated as averaging while adult weight was claimed as .
Relation to age There is a common presumption stated throughout reptilian literature that crocodilians, including the American alligator, exhibit indeterminate growth, meaning the animal continues to grow for the duration of its life. However, these claims are largely based on assumptions and observations of juvenile and young adult crocodilians, and recent studies are beginning to contradict this claim. For example, one long-term mark-recapture study (1979–2015) done at the Tom Yawkey Wildlife Center in South Carolina found evidence to support patterns of determinate growth, with growth ceasing upon reaching a certain age (43 years for males and 31 years for females).
Sexual dimorphism While noticeable in very mature specimens, the sexual dimorphism in size of the American alligator is relatively modest among crocodilians. For contrast, the sexual dimorphism of saltwater crocodiles is much more extreme, with mature males nearly twice as long as and at least four times as heavy as female saltwater crocodiles. Given that female American alligators have relatively higher survival rates at an early age and a large percentage of given populations consists of immature or young breeding American alligators, relatively few large mature males of the expected mature length of or more are typically seen.
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