A new study on Stupendemys geographicus offers new information on this giant turtle

Dr. Rodolfo Sánchez and a male carapace of Stupendemys geographicus (Photo courtesy Edwin Cadena)
Dr. Rodolfo Sánchez and a male carapace of Stupendemys geographicus (Photo courtesy Edwin Cadena)

An article published in the journal “Science Advances” reports a study on Stupendemys geographicus, a giant turtle that lived in today’s South America between 5 and 10 million years ago, in the Miocene period. A team of researchers led by Dr. Marcelo Sánchez of the University of Zurich studied a number of well-preserved carapaces of this animal that provided much more information than the fossils previously available, such as the fact that the males had horns. It was one of the largest turtles ever lived with a carapace that could be up to almost 3 meters long, lived in the areas around fresh water and was probably prey to the gigantic alligators of the genus Purussaurus.

Stupendemys geographicus species was identified in 1976 thanks to fossils discovered in the Urumaco Formation in northwest Venezuela but until recently paleontologists had only a few partial fossils available. This is a common problem in the field of paleontology, even for species that lived in relatively recent times such as this one. This made it difficult to understand the relationships with other turtles, also because today’s species are much smaller while the largest known species, Archelon ischyros, lived much earlier, near the end of the Cretaceous period.

This new study is based on several new Stupendemys geographicus fossils discovered over the years in the Urumaco Formation but also in Colombia and Brazil, showing that it was spread area than previously known. Several fossils are far more complete than the first ones discovered with complete carapaces and other parts such as jaws and horns for male specimens, a discovery that led to the hypothesis of a sexual dimorphism for this species with the males being the only ones having horns.

Some carapaces show bite marks indicating that even an animal as large as Stupendemys geographicus could have been prey. During the Miocene period, alligators with a length of more than 10 meters of the genus Purussaurus such as Purussaurus mirandai and Purussaurus brasiliensis lived in South America. Probably at least one of them is the author of the bite marks found on the turtles.

The discovery of Stupendemys geographicus jaws is also important for paleontologists because it allows an anatomical comparison with other species of turtles. According to the researchers, some turtles that now live in the Amazon region are its closest living relatives, albeit much smaller.

The study of the new fossils of Stupendemys geographicus offered many new information on this giant turtle which also concern its role in the ecosystem in which it lived. The presence of some gigantic animals made the landscape very different from the current one, especially in the areas that today are deserts.

Artist's reconstruction of Stupendemys geographicus (Image courtesy Jaime Chirinos)
Artist’s reconstruction of Stupendemys geographicus (Image courtesy Jaime Chirinos)

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