American alligator


The American alligator, 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 second longest and the heaviest of the family Alligatoridae, 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 Texas to North Carolina. It is distinguished from the sympatric American crocodile by its broader 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, and mammals. 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, 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 in or near the 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.
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, based on the English common name alligator.
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. 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. 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.

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 McIlhenny 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. The largest American alligator scientifically verified in Florida for the period from 1977 to 1993 was reportedly and weighed, although another specimen 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

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 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.

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.

Color

Dorsally, adult American alligators may be olive, brown, gray, or black. However, they are on average one of the most darkly colored modern crocodilians, and can reliably be distinguished by color via their more blackish dorsal scales against crocodiles. Meanwhile, their undersides are cream-colored. Some American alligators are missing or have an inhibited gene for melanin, which makes them albino. These American alligators are extremely rare and almost impossible to find in the wild. They could only survive in captivity, as they are very vulnerable to the sun and predators.

Jaws, teeth, and snout

American alligators have 74–80 teeth. As they grow and develop, the morphology of their teeth and jaws change significantly. Ventral pterygoideus muscles are enlarged and extremely powerful. Juveniles have small, needle-like teeth that become much more robust and narrow snouts that become broader as the individuals develop. These morphological changes correspond to shifts in the American alligators' diets, from smaller prey items such as fish and insects to larger prey items such as turtles, birds, and other large vertebrates. American alligators have broad snouts, especially in captive individuals. When the jaws are closed, the edges of the upper jaws cover the lower teeth, which fit into the jaws' hollows. Like the spectacled caiman, this species has a bony nasal ridge, though it is less prominent. American alligators are often mistaken for a similar animal: the American crocodile. An easy characteristic to distinguish the two is the fourth tooth. Whenever an American alligator's mouth is closed, the fourth tooth is no longer visible. It is enclosed in a pocket in the upper jaw. American alligators also frequently lose and replace their teeth, about once every year. As American alligators live a lengthy life, they can go through over 2,000 teeth in their lifetimes.