We examined the osteology of Neogene Alligator, with a focus on fossils from the late Miocene (~8–7 million years ago [Ma]) Moss Acres Racetrack locality in Marion County, Florida, USA. These fossils have been referred previously to Alligator cf. A. mefferdi (early late Miocene, ~12–10 Ma, Nebraska), an extinct species that we and others have found to be lacking autapomorphic characters. Furthermore, numerous cranial polymorphisms, previously regarded as diagnostic autapomorphies or synapomorphies, exist in several species of Alligator, particularly in Alligator prenasalis (late Eocene–early Oligocene, ~36–33 Ma, South Dakota and possibly Nebraska), Alligator olseni (early Miocene, ~18–17 Ma, Florida), and the extant American Alligator (Alligator mississippiensis; southeastern United States). Except for minute differences in two scapular characters, the fossil Alligator from Moss Acres Racetrack is virtually indistinguishable from the A. mississippiensis morphotype, suggesting its referral to that lineage rather than to an extinct species. Cladistic analysis upholds this notion, with A. mississippiensis and the Moss Acres Racetrack Alligator being sister taxa in a unified clade isolated from A. mefferdi. This implies that the A. mississippiensis morphological lineage has existed in North America with very little change for the past 7–8 million years.
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Vol. 50 • No. 2