The Peninj Mandible(Peninj 1), also called Natron mandible,^[1] is the fossilized lower jaw and teeth of an australopithecine specimen, likely that of Paranthropus boisei^[2] or a similar population.^[3] It was discovered in West Lake Natron,^[4] in Ngorongoro District of Arusha Region of Tanzania by Kamoya Kimeu,^[5][6] Glynn Isaac, and Richard Leakey in 1964.^[7]

This mandible (jaw) is estimated to be 1.5 million years old^[2] and it is characterized as having a robust build with large molars and reduced incisors.^[8] The specimen is believed to be an adult male.^[9]

Peninj 1 was found in 1964 at a site in Tanzania called Peninj, west of Lake Natron and about 80 km (50 miles) from Olduvai Gorge, a major paleoanthropological site.^[10] On the 11th of January, fossil hunter Kamoya Kimeu was crossing the western side of Lake Natron as part of a team led by Richard Leakey when he discovered the mandible buried in ancient volcanic ash in situ.^[11] Later that year, Louis Leakey, his wife Mary Leakey and their son Richard, announced the discovery of the Peninj Mandible in an article published in Nature.^[12]

Together with the OH 5 cranium, the nearly complete mandible of Peninj 1 showed that this East African species was even more robust than other hominin specimens found in southern Africa.^[13]

• List of human evolution fossils