South American turtle fossils, horned shells to protect their skulls.
About five to 10 million years ago, giant turtles that dwarfed humans roamed freshwater swamps in South America. Researchers have uncovered shells belonging to Stupendemys geographicus, the largest turtle that ever existed. Its shell reached nearly 10 feet in length and weighed 2,500 pounds.
By studying the shells and lower jaw fossils, researchers discovered the males had horned shells to protect their skulls. Despite their size, giant bite marks in the shells show that predators, including massive alligator-like caimans, weren’t deterred by the animal’s huge shield.
The new fossil shells were found in Venezuela and Colombia. The turtle was first described in 1976 by paleontologist Roger Wood. He named it Stupendemys for its large size and geographicus in recognition to all the support that National Geographic Society has given to fossil turtle research, according to Edwin Cadena, study author, geologist and vertebrate paleontologist at Del Rosario University in Colombia.
But the new fossils showcase the massive size of the turtles, as well as the giant horned features of the shell close to the turtle’s neck. The horns also helped protect the massive skulls of the males when they fought with other males — females didn’t have this feature.
The study published Wednesday in the journal Science Advances.
Cadena was surprised to uncover the first lower jaw that belonged to this species, “something that we have been searching and waiting to find for decades,” he said.
The lower jaw helps fill in another puzzle piece about these turtles, providing a better idea of their diet. They ate a diverse range of fish, crocodiles, snakes and mollusks, and were able to crush open seeds with their massive lower jawbones, Cadena said.
Although the area where these turtles once lived is now largely desert, it was a humid, swampy freshwater region full of diverse life millions of years ago. And it was the perfect environment for this giant turtle, likely allowing them to reach “unparalleled size.”
“It’s one of the largest, if not the largest turtle that ever existed,” said Marcelo Sánchez, lead study author and director of the Paleontological Institute and Museum of the University of Zurich.
Although they don’t know what exactly caused it to go extinct, researchers know that its habitat was disrupted when the Andes mountains rose and separated the Amazon, Orinoco and Magdalena rivers.
Understanding more about the giant turtle has also helped the researchers clarify turtle evolution and determine that the closest living relative of Stupendemys is the big-headed Amazon river turtle, even though it’s a hundred times smaller. Their diets are similar.
“It shows us that extremely large shells were not only exclusive of marine turtles but also occurred in freshwater turtles,” Cadena said.
“One of the new shells that we described in this publication represents the largest turtle shell so far known in their entire evolution. These findings also help us to understand better the evolution of northern South American turtles and how they interacted with other giant animals that lived in this region approximately 13 million years ago.”
Cadena will search for other turtle fossils in northern South America to learn more about their origin, evolution and relationships with other turtles.
“Being able to reconstruct the life-style and the biology aspects of this giant extinct turtle has been a very exciting project,” Cadena said. “And knowing the evolutionary history of extant species is a key part of to formulate integral plans and educate for their conservation.”