The turtle, which was discovered in 2005 in a coal mine in Colombia and named Carbonemys cofrinii (or coal turtle), is believed to belong to a group of side-necked turtles known as pelomedusoides.
The researchers, who examined the turtle now and detailed their findings in the Journal of Systematic Paleontology, said the turtle's skull, roughly the size of an NFL football, was the most complete of the fossil remains.
In addition to its colossal size, they noted, the turtle would have been equipped with massive, powerful jaws, meaning it could've eaten just about anything in its range, from mollusks (a group that includes snails) to smaller turtles and even crocodiles, LiveScience reported.
Its all-encompassing appetite as well as its need for a large range to satiate its food requirements may explain why no other turtle of this size has been found at the site, the researchers said.
"It's like having one big snapping turtle living in the middle of a lake," said study researcher Dan Ksepka of North Carolina State University. "That turtle survives because it has eaten all of the major competitors for resources."
While the researchers have found bite marks on the remains of other side-necked turtles in the area, suggesting they were preyed upon by crocodilians, such predators would not have messed with this coal mine turtle.
"In fact smaller crocs would have been easy prey for this behemoth," Ksepka said.
Also found nearby the fossils is a turtle shell measuring some 5 feet 7 inches which the researchers believe belonged to the same species.
"The findings gave us the first evidence of gigantism in freshwater turtles," said co-researcher Edwin Cadena, also of North Carolina State.
In fact, this big turtle appeared five million years after the dinosaurs vanished, at a time when gigantism was relatively common in this part of South America, the researchers said.
