Stupendemys is considered to be the second largest turtle, behind seagoing Archelon, which lived roughly 70 million years ago at the end of the age of the dinosaur and reached about 15 feet (4.6 meters) in length.
The male had forward pointing horns either side of its shell.
Such giant crocodiles were probably the reason for the growth of the turtle Stupendemys geographicus.
Traces of scars on the horns suggested that the Stupendemys geographicus may have used these features to defend itself against other turtles or large predators, such as the giant crocodiles that inhabited its natural habitat.
According to Marcelo Sánchez, director of the Paleontological Institute and Museum at the University of Zurich, this indicates that two sexes of the creature existed - with males having horned shells and females having hornless ones.
These freshwater turtles were nearly twice as heavy as the largest ones today relatives still alive: leatherback turtles that live in the warmer seas up to the coasts of Scotland and have a weight of 650 Develop kilograms and a tank of 2, 13 meters.
Based on the size of the shells, the researchers estimated that the Stupendemys geographicus weighed about 1,145 kilograms.
Since the scientists also discovered jaws and other skeleton parts of Stupendemys, they were able to thoroughly revise the evolutionary relationships of this species within the turtle tree of life.
Venezuelan palaeontologist Rodolfo Sánchez and a male carapace of the giant turtle. Image Edwin Cadena
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.
Despite its enormous size, Stupendemys wasn't safe in the Venezuelan swamps.
In the past few years, Cadena's team has been located near Urumaco in the northwest of Venezuela and in the Tatacoa- Desert in the south of Colombia a few more, partly complete tanks and a lower jaw of this type and analyzed them "very carefully", says Uwe Fritz, who was not involved in the investigations. One of the Stupendemys fossils was discovered with a two-inch-long (5 cm) croc tooth embedded in it.
Paleontologists have known about the turtle's existence since the 1970s, but they haven't found enough specimens yet to build a full profile of its behaviours.
"Its diet was diverse including small animals - fishes, caimans, snakes - as well as mollusks and vegetation, particularly fruits and seeds".
A sprawling wetland and lake system meant plenty of room for massive animals - especially the Stupendemys, which spent most of its days at the bottom of freshwater streams and small lakes, Cadena said.