Extinct one-tonne turtle discovered with massive horned shell

12 Feb 2020

A graphic reconstruction of a male Stupendemys geographicus. Image: Jaime Chirinos

The remains of a giant turtle have been discovered with a peculiar and unexpected feature: a horned shell.

A turtle unlike anything alive today once roamed what is now a desert in Venezuela. In a paper published to Science Advances, researchers from Switzerland, Colombia, Venezuela and Brazil revealed the discovery of an exceptional specimen of giant turtle called Stupendemys geographicus, which lived between 5m and 10m years ago.

Measurements of fossilised remains show the creature could grow up to three metres in length, making it one of the largest – if not the largest – turtles that ever existed. It had an estimated body mass of 1,145kg, which is almost 100 times that of its closest living relative, the big-headed Amazon river turtle.

What really surprised the researchers, however, was the discovery that in some of these turtles, their shells featured striking horns for self-defence.

According to Marcelo Sánchez, director of the Paleontological Institute and Museum at the University of Zurich, this indicates that two sexes of the creature existed – with males having horned shells and females having hornless ones.

Rodolfo Sánchez lying beside and dwarfed in size by a fossilised shell of the giant turtle.

Venezuelan palaeontologist Rodolfo Sánchez and a male carapace of the giant turtle. Image: Edwin Cadena

Lingering genetics

Despite its size, the turtle would have had natural enemies, including the Purussaurus – the largest of caimans – which has been found in the area where the giant turtle once lived.

The Purussaurus was most likely a predator of the giant turtle, given not only its size and dietary preferences, but also shown by bite marks and punctured bones in fossil carapaces of Stupendemys.

The discovery of jaws and other skeleton parts of the turtle have allowed the researchers to revise the evolutionary relationships of this species within the turtle tree of life.

“Based on studies of the turtle anatomy, we now know that some living turtles from the Amazon region are the closest living relatives,” Sánchez said.

Also, the new discoveries of fossils from elsewhere in South America suggest it had a wider geographic distribution than previously thought.

Colm Gorey was a senior journalist with Silicon Republic