Temporal range: Late Miocene–Recent
Psammomys obesus, known as the sand rat or fat sand rat, is a terrestrial mammal from the gerbil subfamily that is mostly found in North Africa and the Middle East, ranging from Mauritania to the Arabian Peninsula.
This species usually lives in sandy deserts, but may also be found in rocky terrain or saline marsh areas. It lives in burrows, which are often located under the bushes in which the rats forage, such as salt bushes of the family Chenopodiaceae. The sand rat is diurnal, but its activity on the surface depends on the ambient temperature. The sand rat normally has two litters every year; each litter usually comprises three to seven pups.
Although they remain lean when fed their natural, vegetable-based diet, sand rats can easily become obese and acquire type 2 diabetes mellitus when they are fed a normal rodent diet of grains.  Therefore, they have been used as an animal model for studies on diabetes and obesity.
These animals have been studied extensively for their remarkably efficient kidneys: they can produce very concentrated urine which enables them to eat halophyte plants and survive extreme heat and lack of water in their desert habitat.
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- S. Aulagnier & L. Granjon (2008). "Psammomys obesus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved May 20, 2012.
- Hackel, D. B.; Frohman, L; Mikat, E; Lebovitz, H. E.; Schmidt-Nielsen, K; Kinney, T. D. (1966). "Effect of diet on the glucose tolerance and plasma insulin levels of the sand rat (Psammomys obesus)". Diabetes 15 (2): 105–14. PMID 5907154.
- Kaiser, N; Cerasi, E; Leibowitz, G (2012). "Diet-Induced Diabetes in the Sand Rat (Psammomys obesus)". Animal Models in Diabetes Research 933. pp. 89–102. doi:10.1007/978-1-62703-068-7_7. ISBN 978-1-62703-067-0. PMID 22893403.
- Kalderon, B; Gutman, A; Levy, E; Shafrir, E; Adler, J. H. (1986). "Characterization of stages in development of obesity-diabetes syndrome in sand rat (Psammomys obesus)". Diabetes 35 (6): 717–24. PMID 3519325.
- Tal Ashkenazy, Haim Einat & Noga Kronfeld-Schor (2009). "We are in the dark here: induction of depression- and anxiety-like behaviours in the diurnal fat sand rat, by short daylight or melatonin injections". The International Journal of Neuropsychopharmacology 12 (1): 83–93. doi:10.1017/S1461145708009115. PMID 18631427.
- Michael A. Mares (November 1, 2003). "Desert dreams: seeking the secret mammals of the salt pans". Natural History.