Tortoise fossils provide clues on the rise of Andes Mountains

The discovery of tortoise fossils on a massive, arid plateau in the Andes mountains in southern Bolivia indicates that the area was once no more than one kilometer above sea level, researchers from Case Western Reserve University revealed Tuesday in a statement.

A team led by Case Western anatomy professor and paleomammalogist Darin Croft discovered what turned out to be the fossil remains of the five-foot-long tortoise, as well as pieces of a tinier aquatic turtle, at the Altiplano plateau near what is bow the town of Quebrada Honda.

It marked the first time that turtle fossils dating back to the Miocene epoch have been found in Bolivia, the researchers said, and their discovery indicates that the plateau was far closer to sea level some 13 million years ago than the currently projected 2.0 to 3.2 kilometers.

Furthermore, the findings, which have been detailed in the latest edition of the Journal of South American Earth Sciences, offer a closer look into historical climate change caused by mountains rising, and could also help experts better understand the changes to modern-day climate.

Cold-blooded creatures could not have survived at higher evelations

According to Croft, the tortoise remains were discovered thanks to a fortuitous accident: He saw them in an embankment after making a wrong turn near Quebrada Honda and trying to get back to his regular research site. He and a colleague also later identified additional, more fragmented tortoise remains from other nearby sites.

Upon his return to the US, Croft send photos and 3D computer-generated images to turtle expert Edwin Cadena, now with Ecuador’s Yachay Tech University. Cadena discovered that the tortoise was a member of Chelonoidis, the same genus Galápagos tortoise, and that the smaller turtle was part of the genus Acanthochelys, which includes many South America turtles.

The creatures were cold-blooded, meaning that they relied on the outside air to control their body temperatures, and were likely physiologically similar to their modern relatives, which can’t live at higher altitudes because of the extreme cold, Croft said. This seems to suggest that the Andes, which were formed by subduction, had not reached their current elevation by this time.

He and his colleagues also found additional evidence to support their claims that the mountains were less than one kilometer high during the late Miocene—including the fossil remains of a large snake in the same rock layer as the turtles. If this is the case, it means that the Andes would have had far less on an impact on global air circulation patterns than they would have had they been closer to their current height.

“We’re trying to understand how tectonic plate activity and changing climate affected species diversity in the past… Mountains create many different climates and ecosystems in a small area, which promotes speciation,” Croft said in a report on Phys.org. “With current global climate change, we’d like to have a better idea of what to expect under different scenarios – how 1-degree warming or 2-degree warming will affect sea levels and animals.”

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Feature Image: Darin Croft

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