Stupendemys was a giant prehistoric aquatic (water-dwelling) turtle. Stupendemys lived during the Miocene Epoch, around 23 million to 5.3 million years ago. Its closest living relative is the big-headed Amazon river turtle.
Stupendemys had a big head with a sharp beak. It had four paddlelike limbs and a short tail. It probably could not withdraw its head or limbs into its large shell, as can many turtles. Its shell alone measured about 8 feet (2.4 meters) long.
Stupendemys weighed about 2,500 pounds (1,150 kilograms). It and the prehistoric marine turtle Archelon were the largest turtles known to have ever lived. In comparison, the largest living turtle, the leatherback sea turtle, grows up to 8 feet (2.4 meters) long and can weigh up to 2,000 pounds (900 kilograms).
Some fossil shells of Stupendemys have large, forward-pointing horns at the shoulders. Scientists think perhaps only males had these horns. They may have used the horns to compete for mates and defend their territory.
Paleontologists discovered fossils of Stupendemys in northern South America, in what is now the Amazon River Basin. During the Miocene Epoch, the region was covered by a network of rivers flowing into a shallow sea. Stupendemys lived in these rivers. It probably ate mollusks and large fruits and seeds.
