Avisaurus (meaning "bird lizard") is an extinct genus in a group of Cretaceous birds called Enantiornithes. Two species are known; the type species A. archibaldi, and A. gloriae. Both are known only from single fossilized bones of the foot - the tarsometatarsus. Both species of Avisaurus are known from the humid low-lying swamps, lakes, and river basins of the western shore of the Western Interior Seaway, and from the much more arid uplands between that area and the Cordilleran Overthrust Belt which eventually formed the Rocky Mountains.