Imagine a giant turtle the size of an average car with a shell large enough to double as a kiddie pool.
Paleontologists from North Carolina State University (NCSU) have found just such a specimen -- the fossilized remains of a 60-million-year-old South American giant that lived in what is now Colombia.
The turtle 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 Irrejon formation, the Journal of Systematic Palaeontology reports.
The specimen's skull measures 24 cm, 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 cms, or about 5 feet 7 inches, long. That's the same height as Edwin Cadena, the NCSU doctoral student who discovered the fossil, according to a North Carolina statement.
"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," Cadena says.
Smaller relatives of Carbonemys existed alongside dinosaurs. But the giant version appeared five million years after the dinosaurs vanished, during a period when giant varieties of many different reptiles -- including Titanoboa cerrejonensis, the largest snake ever discovered -- lived in this part of South America.
Researchers believe that a combination of changes in the ecosystem, including fewer predators, a larger habitat area, plentiful 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 delta.
In addition to the turtle's huge size, the fossil also shows that this particular turtle had massive, powerful jaws that would have enabled the omnivore to eat anything nearby -- from molluscs to smaller turtles or even crocodiles.
Thus far, only one specimen of this size has been recovered. 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.