Mummified mice found in Andes at altitude previously thought uninhabitable for mammals

Mummified mice found atop the Andes demonstrate that mammals can survive at much higher altitudes than previously believed.

Researchers have discovered rodents living at over 20,000 feet on the summits of volcanoes in the Puna de Atacama region of Chile and Argentina.

Previously, it was thought that surviving in such extreme conditions, where oxygen levels are about half that at sea level, was impossible for mammals, with none observed beyond 17,000 to 19,000 feet.

Archaeologists had found mouse remains at the Andes' peaks in the 1970s, but it was believed they were carried up by Inca people journeying to the summits for child sacrifices.

However, Professor Jay Storz from the University of Nebraska captured a live leaf-eared mouse at the 22,000-foot summit of Llullaillaco volcano and found 13 mummified mice on nearby peaks.

Dating these mummified mice revealed some were only a few decades old, indicating they could not have been transported by the Inca.

“These are essentially freeze-dried, mummified mice,” said Prof. Storz. “It now seems more and more clear that they are there of their own accord.”

“Even at the base of the volcanoes, the mice are living in an extreme, Martian environment. On the summits, it’s even more so. It feels like outer space.

“It’s mind-boggling that any kind of animal, especially a warm-blooded mammal, could survive and function in that environment. Experiencing it firsthand further impresses upon you: How is anything living up there?”

Mars-like Conditions

The Puna de Atacama is one of the most inhospitable places on Earth, being so arid, cold, and oxygen-poor that NASA uses it to practice searching for life on Mars.

Experts are puzzled as to why the mice live in such a harsh environment, but suggest they may be avoiding predators like foxes and mountain lions.

“Certainly, if you’re on top of a 6,000-meter volcano, you’re safe from those,” added Prof. Storz. “You just have other things to worry about.

“But why they ascend to these extreme elevations remains a mystery.”

The team studied the mice’s DNA to see if they had developed mutations enabling them to survive at high altitudes but found no differences from lower-dwelling rodents.