[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.

[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.

[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.