Stupendemys

Stupendemys is an extinct genus of freshwater side-necked turtle, belonging to the family Podocnemididae. It is the largest freshwater turtle known to have existed, with a carapace over 2 meters long. Its fossils have been found in northern South America, in rocks dating from the Middle Miocene to the very start of the Pliocene, about 13 to 5 million years ago. Male specimens are known to have possessed bony horns growing from the front edges of the shell and the discovery of the fossil of a young adult shows that the carapace of these turtles flattens with age. A fossil skull described in 2021 indicates that Stupendemys was a generalist feeder.

==History and naming== Stupendemys was first named in 1976 by Roger C. Wood based on specimen MCNC-244, the medial portion of a large sized carapace with associated left femur, scapulacoracoid and a cervical vertebra. Wood also described several other specimens he referred to Stupendemys, which includes MCZ(P)-4376. This specimen preserves much of the carapace alongside a fragmented plastron and various other bones. The fossils were unearthed by a paleontological excavation of the Harvard University in Venezuela in 1972. In 2006 a second species, Stupendemys souzai was described by Bocquentin and Melo based on material from the Solimões Formation in Acre State in Brazil, also home to the giant Caninemys. In February 2020, Cadena and colleagues published a paper describing material discovered during the routine excavations in the Urumaco Formation, which have been ongoing since 1994. The material includes a relatively complete carapace that set a new maximum size for the genus and was designated as the allotype, meaning the specimen is of the opposite sex of the holotype. Venezuela also yielded fossils of a lower jaw, which has been used to lump Caninemys into Stupendemys in the 2020 study. The authors likewise consider S. souzai to be synonymous with S. geographica. However, more fossils were discovered in the Colombian Tatacoa Desert and formally described by Cadena and colleagues in 2021, including the first definitive skull remains as well as the first remains of a juvenile or early adult specimen (carapace length under 1 meter). The La Victoria Formation also yielded the remains of an adult female as well as more fossils of Caninemys. With definitive skull remains of Stupendemys known in association with a carapace and new fossils of Caninemys, the referral of Caninemys' skull to Stupendemys was contested and the former was re-established as a valid genus.