Eonatator is a genus of halisaurine mosasaur from the Upper Cretaceous of North America, South America and Europe. Originally, this taxon was included within Halisaurus, but was placed in its own genus. Eonatator is known from the Smoky Hill Chalk Member of the Niobrara Chalk Formation (Upper Coniacian - Lower Campanian) of Kansas, from the Eutaw Formation (Santonian) and Mooreville Chalk Formation (Selma Group; Santonian-Lower Campanian) of Alabama (United States), from the Kristianstad Basin of southern Sweden (late early Campanian), and the unit Nivel de Lutitas y Arenas (Campanian) in La Mesa, Colombia. The name Eonatator means "dawn swimmer" (Greek eos = dawn + Latin natator = swimmer). Originally it contains only a single species, E. sternbergii. The species is named in honour of Cha