Fat sand rat

The fat sand rat, Psammomys obesus, is a terrestrial gerbil found mostly in North Africa and the Middle East, ranging from Mauritania to the Arabian Peninsula. It lives mainly in sandy desert but may also be found in rocky terrain or saline marsh. It eats only the stems and leaves of plants of the amaranth family, Amaranthaceae, such as Atriplex halimus, which supply its water so that it needs no standing water. Unusually for a desert rodent it is diurnal and solitary, with each animal in its own burrow dug beneath the shrubs it feeds on. Its average lifespan is about 14 months in the wild and three to four years in captivity. Fed an ordinary rodent grain diet it becomes obese and develops type 2 diabetes, so it is used as a model for diabetes and for seasonal affective disorder. Its kidneys produce very concentrated urine, which lets it eat halophyte plants in extreme heat.