Picture a turtle the size of a Smart car, with a shell large enough to double as a kiddie（小孩） pool. Paleontologists from North Carolina State University have found just such a specimen¹ -- the fossilized remains² of a 60-million-year-old South American giant that lived in what is now Colombia. The turtle in question is Carbonemys cofrinii, which means "coal turtle," and is part of a group of side-necked turtles known as pelomedusoides. The fossil was named Carbonemys because it was discovered in 2005 in a coal mine that was part of northern Colombia's Cerrejon formation. The specimen's skull³ measures 24 centimeters, roughly the size of a regulation NFL football. The shell which was recovered nearby -- and is believed to belong to the same species -- measures 172 centimeters, or about 5 feet 7 inches, long. That's the same height as Edwin Cadena, the NC State doctoral student who discovered the fossil.

"We had recovered smaller turtle specimens⁴ 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," Cadena says.

Smaller relatives of Carbonemys existed alongside dinosaurs⁵. But the giant version appeared five million years after the dinosaurs vanished, during a period when giant varieties of many different reptiles⁶ -- including Titanoboa cerrejonensis, the largest snake ever discovered -- lived in this part of South America. Researchers believe that a combination of changes in the ecosystem⁷, including fewer predators⁸, a larger habitat area, plentiful⁹ food supply and climate changes, worked together to allow these giant species to survive. Carbonemys' habitat would have resembled a much warmer modern-day Orinoco or Amazon River delta¹⁰.

In addition to the turtle's huge size, the fossil also shows that this particular turtle had massive, powerful jaws¹¹ that would have enabled the omnivore（杂食动物） to eat anything nearby -- from mollusks（软体动物） to smaller turtles or even crocodiles.

Thus far, only one specimen of this size has been recovered. Dr. Dan Ksepka, NC State paleontologist and research associate at the North Carolina Museum of Natural Sciences, believes that this is because a turtle of this size would need a large territory in order to obtain enough food to survive. "It's like having one big snapping turtle living in the middle of a lake," says Ksepka, co-author of the paper describing the find. "That turtle survives because it has eaten all of the major competitors for resources. We found many bite-marked shells at this site that show crocodilians preyed¹³ on side-necked turtles. None would have bothered an adult Carbonemys, though -- in fact smaller crocs would have been easy prey¹² for this behemoth（巨兽，河马） ."

The paleontologists' findings appear in the Journal of Systematic¹⁴ Palaeontology. Dr. Carlos Jaramillo from the Smithsonian Tropical Research Institute in Panama and Dr. Jonathan Bloch from the Florida Museum of Natural History contributed to the work. The research was funded by grants from the Smithsonian Institute and the National Science Foundation.