A team of paleobiologists has discovered exceptional fossil specimens of an extinct giant freshwater turtle in Venezuela and Colombia. The enormous turtle – a species from the genus Stupendemys – lived 5 to 10 million years ago in lakes and rivers of what’s now northern South America. Stupendemys was one of the biggest turtles that ever lived, with a shell that measured about 8 to almost 10 feet (2.4-3 meters). What’s more, it turns out that the shell of the male Stupendemys had horns, a rare feature in turtles.
The new specimens were from Stupendemys geographicus, a turtle species first described in the mid-1970s. The finds included the largest shell reported for any turtle ever – living or extinct – with a carapace (upper shell) length of 8 feet (2.4 meters) and estimated body mass of 2,500 pounds (1,145 kg), almost 100 times the size of its closest living relative, the big-headed Amazon river turtle.
Stupendemys geographicus was huge and heavy. The largest individuals of this species were about the size and length of a sedan automobile if we take into account the head, neck, shell and limbs.
The two shell types indicate that two sexes of Stupendemys existed: males with horned shells, and females with hornless shells
According to Sánchez, this is the first time that sexual dimorphism – distinct differences in size or appearance between the sexes of a species – in the form of horned shells has been reported for any of the side-necked turtles, one of the two major groups of turtles world-wide.
According to a statement from the researchers:
Despite its tremendous size, the turtle had natural enemies. In many areas, the occurrence of Stupendemys coincides with Purussaurus, the largest caimans. This was most likely a predator of the giant turtle, given not only its size and dietary preferences, but also as inferred by bite marks and punctured bones in fossil carapaces of Stupendemys.
Since the scientists also discovered jaws and other skeleton parts of Stupendemys, they were able to revise the evolutionary relationships of this species in the turtle tree of life. Sánchez said:
Based on studies of the turtle anatomy, we now know that some living turtles from the Amazon region are the closest living relatives.
Bottom line: Fossils shed new light on an enormous horned turtle that roamed South America 5 to 10 million years ago.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as an EarthSky.org Editor, she helps present the science and nature stories and photos you enjoy. She and her husband live in Tennessee, where they enjoy guitar playing and singing. They have 2 grown sons.