The Mongolian gerbil or Mongolian jird (Meriones unguiculatus) is a small rodent belonging to the subfamily Gerbillinae. Their body size is typically 110–135 mm (4+1⁄4–5+1⁄4 in), with a 95–120 mm (3+3⁄4–4+3⁄4 in) tail, and body weight 60–130 g (2–4+1⁄2 oz), with adult males larger than females. The animal is used in science and kept as a small house pet. Their use in science dates back to the latter half of the 19th century, but they only started to be kept as pets in the English-speaking world after 1954, when they were brought to the United States. However, their use in scientific research has fallen out of favor.