Quirks & Quarks

The largest turtle that ever lived had fighting horns on its shell

This freshwater turtle was the size of a small car, and lived in the north part of South America 12 million years ago.

This freshwater turtle was the size of a small car

Venezuelan paleontologist Rodolfo Sanchez and the shell of the male giant turtle Stupendemys geographicus. (Jorge Carillo)

New fossil evidence helps fill in the story of the largest turtle of all time. Stupendemys geographicus was up to four metres long, weighed more than a ton and had fighting horns that protruded from its shell near its head.

Stupendymys was first identified in the 1970s but new fossils have been unearthed in Venezuela and Columbia, meaning researchers now have the remains of seven individuals. These allowed Edwin Cedena, an associate professor in the Earth System Science Program at the University of Rosario in Bogota, Colombia, and his colleagues to fill in many biological and evolutionary gaps, including those related to its impressive size.

Image of the giant turtle Stupendemys geographicus (Jaime Chrinos)

Largest turtle of all time

The shell of the largest Stupendemys found so far was three metres long, and the researchers estimate the living turtle would have weighed 1,145 kilograms. That makes it 100 times larger than its closest living relative, the Amazon river turtle, and twice the size of the largest living turtle, the marine leatherback. It lived in the Miocene epoch, between 13 million and seven million years ago in northern South America.

Colombian paleontologist Edwin Cadena, taking notes from one of the male specimens of Stupendemys geographicus (Rodolfo Sanchez)

Horned shell

The most recent specimens allowed Cedena and his colleagues to see complete shells for the first time. This revealed horns at the front of the upper shell on the male only. These were likely for protection in male-to-male combat, and in fact showed scars apparently made by rival turtles' corresponding horns.

Their size and shell didn't completely protect the giant turtles. One shell still contained an embedded tooth from a predatory crocodile as well as other bite marks.

Stupendemys male (Edwin Cadena)

The discovery of a mandible, or lower jaw, also revealed clues about the lifestyle of Stupendemys. Flat bones on the lower jaw suggest a snapping type of bite powerful enough to hold much larger prey and crush bones and shells of smaller turtles.           

The Andes rise, Stupendemys falls

Stupendemys lived in a very large wetland that existed in the northern part of South America. The turtle thrived in this habitat and was able to grow so big because there was plenty of space, an abundance of food and consistently warm temperatures. 

Unfortunately, the uplifting of what would become the Andes mountain range started to transform and fragment those wetlands. Cadena believes this change in habitat may have contributed to the ultimate extinction of this giant turtle.

Fieldwork site in Venezuela (Edwin Cadena)

Written and produced by Mark Crawley   

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