On top of Volcán Llullaillaco in northern Chile, scientists captured the yellow-rumped leaf-eared mouse at 6,739 meters above sea level (22,000 feet). The small creature, whose identity was verified through DNA sequence analysis, holds a big record: highest dwelling mammal in the world. It was found far above the hypothesized altitudinal limit for mammals of 5800 m (19,000 feet). 

Life at such high elevations is physiologically taxing, so these mice raise big questions. Have they evolved adaptations to low-oxygen compared to their lower dwelling relatives? And perhaps more puzzling, what are they eating at an elevation over 2000 m higher than green plants survive? This discovery highlights how much we still don’t know about high-elevation ecosystems and the organisms that live in them.