Stupendemys is a prehistoric genus of freshwater turtle. Its fossils have been found in northern South America, in rocks dating from the late Miocene to the very start of the Pliocene, about 6 to 5 million years ago. Two species have been described to date. Stupendemys geographicus was more robust; its remains have been found in the Urumaco Formation of Venezuela. Stupendemys souzai, marginally smaller and more slender, was recovered from the Solimões Formation in Acre State, Brazil.