Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. The two extant species are the American alligator (A. mississippiensis) and the Chinese alligator (A. sinensis). Additionally, several extinct species of alligator are known from fossil remains. Alligators first appeared during the Oligocene epoch about 37 million years ago.[1]
The name "alligator" is probably an anglicized form of el lagarto, the Spanish term for "the lizard", which early Spanish explorers and settlers in Florida called the alligator.[2] Later English spellings of the name included allagarta and alagarto.[3]
Alligators and caimans split in North America during the early Tertiary or late Cretaceous (about 53 million to about 65 million years ago).[4][5] The Chinese alligator split from the American alligator about 33 million years ago[4] and likely descended from a lineage that crossed the Bering land bridge during the Neogene. The modern American alligator is well represented in the fossil record of the Pleistocene.[1] The alligator's full mitochondrial genome was sequenced in the 1990s.[6] The full genome, published in 2014, suggests that the alligator evolved much more slowly than mammals and birds.[7]
The genus Alligator belongs to the subfamily Alligatorinae, which is the sister taxon to Caimaninae (the caimans). Together, these two subfamilies form the family Alligatoridae. The below cladogram shows the phylogeny of alligators.[8][9]
An average adult American alligator's weight and length is 360 kg (790 lb) and 4 m (13 ft), but they sometimes grow to 4.4 m (14 ft) long and weigh over 450 kg (990 lb).[10] The largest ever recorded, found in Louisiana, measured 5.84 m (19.2 ft).[11] The Chinese alligator is smaller, rarely exceeding 2.1 m (7 ft) in length. Additionally, it weighs considerably less, with males rarely over 45 kg (100 lb).
Adult alligators are black or dark olive-brown with white undersides, while juveniles have bright yellow or whitish stripes which sharply contrast against their dark hides, providing them additional camouflage amongst reeds and wetland grasses.[12]
