The Stupendemys geographicus was approximately the dimension of an automobile.
One of the specimens described in the latest study - published this week in the journal Science Advances - boasted a shell almost 10 feet across. Paleobiologists discovered exceptional specimens in Venezuela and Colombia.
The tropical region of South America is one of the world's hot spots when it comes to animal diversity.
The giant turtles, from the species named Stupendemys geographicus first described in the 1970s, roamed a humid, swampy swath of the continent that was also home to giant rodents, crocodiles and alligators between five and ten million years ago.
One of the largest turtles that ever lived prowled the lakes and rivers of northern South America from about 13 million years ago to 7 million years ago - and this car-sized freshwater beast was built for battle.
It shared their environment with 36-foot-long crocodilians. It had an estimated body mass of 1,145kg, which is nearly 100 times that of its closest living relative, the big-headed Amazon river turtle.
Interestingly, some individuals exhibited an unexpected feature: horns on the carapace. Since the giant tortoises swallow very large fruits and their seeds could be excreted from some distance away, Stupendemys geographicus probably had an important distribution role in the ecosystem.
Researchers suggest the unique horn-like shells at the front of the hard upper shells, may have served to protect their massive skulls when engaged in combat with other males.
Despite its tremendous size, the turtle had natural enemies. The size and dietary preferences of Purussaurus also back this up.
The huge extinct freshwater turtle Stupendemys geographicus, which lived in lakes and rivers in northern South America during the Miocene Epoch, is seen in an illustration released February 12, 2020. Some of the giant turtle fossils featured bite marks and punctured bones.
"Based on studies of the turtle anatomy, we now know that some living turtles from the Amazon region are the closest living relatives", Sánchez said.
Stupendemys was first discovered in the mid-1970s, but an global team of researchers from Colombia, Venezuela, Brazil, and Switzerland, has now reported exceptionally well-preserved specimens of the extinct turtle - in the process - and we now know that this turtle was much more interesting than initially thought. Edwin Cadena from the Universidad del Rosario in Bogotá, the capital of Colombia, and his colleagues in the journal Science Advances appreciate this.