The  family Alligatoroidea includes all crocodilians that are more closely related to the American alligator than to the Nile crocodile.

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Members of this family first arose in the late Cretaceous.  Fossil alligatoroids have been found throughout Eurasia as land bridges across both the North Atlantic and the Bering Strait have connected North America to Eurasia during the Cretaceous, Paleogene, and Neogene periods.

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Alligators and caimans split in North America during the late Cretaceous and the latter reached South America by the Paleogene, before the closure of the Isthmus of Panama during the Neogene period. The Chinese alligator 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.