The alligator snapping turtle (Macrochelys temminckii) is a large species of turtle in the family Chelydridae. The species is native to freshwater habitats in the United States. M. temminckii is one of the heaviest freshwater turtles in the world. It is the largest freshwater species of turtle in North America. It is often associated with, but not closely related to, the common snapping turtle, which is in the genus Chelydra.