Turtle Fossils Shed Light On Rise Of Andes Mountains

Fossil remains of a five-foot-long tortoise suggest the Andes Mountains sat less than a kilometer above sea level 13 million years ago. These fossils, along with smaller aquatic turtle and large snake remains, also indicate the climate was much wetter than today, according to researchers from Case Western Reserve University.

"We're trying to understand how tectonic plate activity and changing climate affected species diversity in the past," Darin Croft, paleomammalogist and anatomy professor from Case Western Reserve University, explained in a news release. "One way all this diversity we see in the South American tropics today was generated was through elevation. Mountains create many different climates and ecosystems in a small area, which promotes speciation."

Researchers stumbled upon the fossils hidden among Bolivia's arid Altiplano, which is a plateau located near what is now the town of Quebrada Honda. Using photographs and 3D computer-generated images, researchers determined the tortoise was a member of the same genus as the Galápagos tortoise, Chelonoidis. Additionally, the extinct freshwater turtle belonged to the genus Acanthochelys, whose surviving members can be found throughout much of tropical South America. Since these animals are ectotherms, their body temperature is dependent on the air around them--so researchers are able to interpret the past climates in which these animals lived, as well as the elevation of their habitat. 

Similar to their modern relatives, the ancient tortoise and aquatic turtle would have most likely lived at altitudes of up to about 500 meters, since higher altitudes have colder, inhabitable climates. This suggests the Andes were once much lower than they are today. Although researchers previously found the mountains formed by subduction - a process in which one tectonic plate is shoved under another - how quickly the mountains rose to their current elevation remains a mystery. 

"With current global climate change, we'd like to have a better idea of what to expect under different scenarios - how one-degree warming or two-degree warming will affect sea levels and animals," Croft continued. "If we want to model the future, we need to understand and model the past."

While the Andes Mountains -- the highest geological feature in South America -- play a key role in global climate change and air circulation patterns today, this was not the case 13 million years ago. Instead, the land features at less than one kilometer above sea level would have had a much smaller effect on global circulation, researchers conclude. Their study was recently published in the Journal of South American Earth Sciences.

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