Dubbed Carbonemys cofrinii, or "coal turtle," the fossil was discovered in a coal mine in Colombia, researchers from North Carolina State University reported Thursday.
The fossilized shell was about 5 feet 7 inches long, about the size of a Smart car, and the fossilized skull had massive, powerful jaws that would have enabled the omnivore to eat anything from mollusks to smaller turtles or even crocodiles, researchers said.
"We had recovered smaller turtle specimens from the site. But after spending about four days working on uncovering the shell, I realized that this particular turtle was the biggest anyone had found in this area for this time period -- and it gave us the first evidence of giantism in freshwater turtles," NC State doctoral student Edwin Cadena said.
Smaller relatives of Carbonemys existed alongside dinosaurs but the giant version appeared five million years after the dinosaurs vanished, researchers said, during a period when giant varieties of many different reptiles, including the largest snake ever discovered, lived in this part of South America.