These Car-Sized Turtles Once Prowled The Lakes And Rivers Of Northern South America

Though it is now arid, the Urumaco region in Venezuela's Falcón State was once a mega wetland that was home to numerous colossal animal species. These included rodents the size of modern-day buffaloes and 10-foot (3-meter) tall carnivorous birds. The latest to join the list of the area's massive creatures is a giant turtle that was 100 times larger than its closest living relative, the Amazon river turtle, and about 1.5 times the size of the world's largest living turtle, the marine leatherback.

Researchers first became aware of the Stupendemys (stupendous turtle) geographicus in 1976, after a Harvard paleontologist unearthed a few fossils. However, the small fragments found were not enough to ascertain what the freshwater turtle looked like, or how it behaved. Now, a team led by the University of Zurich's Marcelo Sánchez has discovered pristinely-preserved turtle shells and jawbone fossils in the Urumaco region and Colombia's Tatacoa Desert, enabling scientists to gain insights into the giants, which roamed Northern South America between 8 and 13 million years ago.

"For almost four decades, we didn't have new and excellently preserved fossils of this turtle," said Edwin Cadena, a paleontologist at the Universidad del Rosario in Colombia and one of the study's lead researchers. "Many questions — about its diet, if there were differences between males and females, and even if we were dealing with one or more giant turtle species — were completely unknown."

The team's findings, published in the journal Science Advances on February 12, 2020, reveal that the massive animals sported a 9-foot-long shell and weighed more than 2,500 pounds (1133 kilograms), or about as much as an average car. The front-facing horns on the shells of the male turtles are believed to have been used as weapons in male-to-male combat. The behavior is prevalent in modern-day snapping turtles whose males often fight each other to establish dominance in overlapping territories.

The horns may have also been used to fend off the huge alligator-like caimans, which were about 34 feet long and may have weighed up to 18,500 pounds, or about seven times the weight of the giant turtles. Bite marks on a female turtle shell and a massive tooth embedded in another carapace confirmed the scientists' suspicions that predatory attacks were a way of life for the giant creatures.

Though they lived among ruthless predators, the turtles themselves were gentle giants who used their massive size to stay close to the riverbeds to graze on underwater plants and munch on hard-shelled mollusks. The researchers believe that the turtles' large size may have hindered their ability to swim, making them easy targets to hunt down.

Cadena says, "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. Its diet was diverse, including small animals – fishes, caimans, snakes – as well as mollusks and vegetation, particularly fruits and seeds. Putting together all the anatomical features of this species indicates that its lifestyle was mostly in the bottom of large freshwater bodies, including lakes and large rivers."

The giant turtles were once widespread throughout the Pebas system — a large network of rivers and wetlands that extended from northwest Brazil through Peru and Colombia, and to the coast of Venezuela. Unfortunately, geological forces, which uplifted the Andes mountains about 8 million years ago, caused the area to become dry, ending the lives of all the majestic animals who inhabited the regions.

Resources: Forbes.com, advances.sciencemag.org, phys.org