Discovery of the world's highest-dwelling mammal

Environmental limits of animal life are invariably revised upwards when the animals themselves are investigated in their natural habitats. Here we report results of a scientific mountaineering expedition to survey the high-altitude rodent fauna of Volcan Llullaillaco in the Puna de Atacama of northern Chile, an effort motivated by video documentation of mice (genus Phyllotis) at a record altitude of 6205 m. Among numerous trapping records at altitudes >5000 m, we captured a specimen of the yellow-rumped leaf-eared mouse (Phyllotis xanthopygus rupestris) on the very summit of Llullaillaco at 6739 m. This summit specimen represents an altitudinal world record for mammals, far surpassing all specimen-based records from the Himalayas and elsewhere in the Andes. This discovery suggests that we may have generally underestimated the altitudinal range limits and physiological tolerances of small mammals simply because the worlds highest summits remain relatively unexplored by biologists.