Tanzanonautes tuerkayi is a species of fossil freshwater crab from Tanzania, the only species in the genus Tanzanonautes.^[1] It is the oldest known freshwater crab, and probably dates from the Oligocene;^[1][2] the next oldest specimens are from the Miocene.^[1] A number of fragmentary remains were discovered in the Songwe Valley part of the East African Rift in Mbeya Region, Tanzania (approximately 8°56′S 33°12′E), in fragile sandstone sediments.^[1] The animal had a carapace around 50 millimetres (2.0 in) across the widest part, which is around 15 mm (0.6 in) from the front of the carapace; the carapace is 44 mm (1.7 in) from front to back, and the slightly inward-curving rear edge of the carapace is 28 mm (1.1 in) across.^[1] The genus name refers to Tanzania, the country where the fossil was found, while the specific epithet commemorates Michael Türkay, an authority on freshwater crabs.^[1] The genus Tanzanonautes is assigned to the family Potamonautidae, although the characters mentioned in the family's diagnosis are missing from the fragmentary fossils available.^[1]