Leviathanochelys
{{Speciesbox | fossil_range = | image = Leviathanochelys.png | image_caption = Type material of Leviathanochelys'| genus = Leviathanochelys | parent_authority = Castillo-Visa et al., 2022 | species = aenigmatica | authority = Castillo-Visa et al., 2022 }}Leviathanochelys is an extinct genus of giant sea turtle from the Middle Campanian of northern Spain. Although only known from the rear end of the carapace and the connecting pubic bones, these elements clearly show that they belonged to a turtle of great size, comparable in dimensions to the giant Archelon and Protostega from the Western Interior Seaway of the USA. This makes Leviathanochelys the first giant sea turtle known from Europe and one of the largest known turtles of all time. This great size was evolved independently from the American protostegid turtles and was likely an adaptation to the conditions of the Cretaceous oceans covering much of Europe. Being classified in the superfamily Chelonioidea, Leviathanochelys is likely more closely related to modern sea turtles (families Dermochelyidae and Cheloniidae) than the protostegids, which are thought to be more basal and have a more uncertain relationship to modern sea turtles. Leviathanochelys is thought to have been a pelagic animal. The genus contains a single species,