The desert armadillo (Chaetophractus vellerosus) survives in portions of the Monte Desert of Argentina where rainfall is as low as 130 millimeters per year. The nine-banded armadillo (Dasypus novemcinctus) is not able to exist in arid areas because of a dependence on water. Measurements of kidney relative medullary thickness (RMT) indicate that the Chaetophractus kidney has a higher concentrating ability than expected for a xeric mammal of its weight. The efficiency of the Dasypus kidney is lower than expected for a xeric mammal yet higher than a mesic mammal. On a dehydrated meat diet, Chaetophractus is able to remain in water balance whereas Dasypus is not.