The remains of an extinct giant turtle species suggest the reptile exhibited sexual dimorphism, with males boasting horned shells and females growing hornless shells.

The turtle fossils were recovered from dig sites in Venezuela and Colombia. Today, the northern tip of South America is quite arid and covered in desert sands, but some 5 to 10 million years ago, during the Miocene epoch, the region was humid and swampy.

Many large species called the tropical hotspot home during the Miocene, including giant rodents and crocodylians. The ancient South American swamps were also home to Stupendemys geographicus, one of the world's largest turtles.

Thanks to the recovery and analysis of several exceptionally preserved Stupendemys geographicus specimens, scientists have gained new insights into the physiology and anatomy of the giant turtle.

For the first time, scientists identified horns on the shells of male Stupendemys geographicus specimens.

"The two shell types indicate that two sexes of Stupendemys existed -- males with horned shells, and females with hornless shells," Marcelo Sánchez, director of the Paleontological Institute and Museum of University of Zurich in Switzerland, said in a news release.

It's the first time scientists have found evidence of sexual dimorphism in side-necked turtles, one of the two major turtle groups.

One of the specimens described in the latest study -- published this week in the journal Science Advances -- boasted a shell nearly 10 feet across.

Through analysis of the ancient turtle fossils, scientists determined mature Stupendemys geographicus specimens weighed upwards of 2,500 pounds.

Despite their hulking size and massive shells, the giant turtles weren't without natural predators. The extinct species lived alongside members of Purussaurus, an extinct genus of giant caiman. Some of the giant turtle fossils featured bite marks and punctured bones.

The new research provided scientists an improved understanding of the species' position within the turtle family tree.

"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.

The latest findings also showed the giant turtle enjoyed a much wider range than previously realized. The massive reptile lived across the entirety of the northern part of South America.

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