Alligator. An alligator, or colloquially gator, is a large reptile in the Crocodilia order in the genus Alligator of the family Alligatoridae.
   The two extant species are the American alligator and the Chinese alligator. Additionally, several extinct species of alligator are known from fossil remains.
   Alligators first appeared during the Oligocene epoch about 37 million years ago. Alligators and caimans split in North America during the early Tertiary or late Cretaceous.
   The Chinese alligator split from the American alligator about 33 million years ago and probably 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.
   The alligator's full mitochondrial genome was sequenced in the 1990s. The full genome, published in 2014, suggests that the alligator evolved much more slowly than mammals and birds. The genus Alligator belongs to the subfamily Alligatorinae, which is the sister taxon to Caimaninae. Together, these two subfamilies form the family Alligatoridae. An average adult American alligator's weight and length is 360 kg and 4 m, but they sometimes grow to 4.4 m long and weigh over 450 kg. The largest ever recorded, found in Louisiana, measured 5.84 m. The Chinese alligator is smaller, rarely exceeding 2.1 m in length. Additionally, it weighs considerably less, with males
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