Saturday, 26 May 2012

A Giant Turtle From The Cretaceous Coal Rivers

The shell of Carbonemys cofrinii. in direct comparison to Edwin Cadena
60 million years ago, the waterways of what would become South America, were haunted by an armored giant: a species of turtle similar in size to a Smart car. Over the decades, palaeontologists have unearthed many different species.

While varying in terms of preservation and completeness, we have built up a fairly comprehensive record of their evolutionary history. We know that turtles appeared some 215 million years ago and comfortably escaped the cataclysmic Cretaceous extinction event. Today they are a diverse group. Yet occasionally the fossil record throws up surprises.

In 2005, palaeontologists from North Carolina State University unearthed the remains of a chelonian (the proper name for a turtle) from a coal mine in the Cerrejon Region of Columbia. After the 60 million year old coal and rock had been cleaned from the bones, which comprised a skull and a shell from two different specimens, analysis began.

The skull alone was 24 centimeters in length, the shell 172 centimeters in diameter. It was like nothing else in the fossil record of the time. The researchers named it Carbonemys cofrinii which translates as 'coal turtle.' '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,' said Edwin Cadena from North Carolina State University and leader of the research team.

Their results suggest that Carbonemys was a vicious predator. The jaws were large and deep muscle grooves show that its bite was very powerful. Its overall size meant that it could have fed on anything from crocodilians to molluscs. 'It's like having one big snapping turtle living in the middle of a lake,'says Ksepka, co-author on the project. Carbonemys survived by eating the competition. Bite-marked shells found at the site showed that crocodillians preyed on side-necked turtles. Yet nothing disturbed the adult Carbonemys.