"P. aethiopicus" is the earliest member of the genus, with the oldest remains, from the Ethiopian Omo Kibish Formation, dated to 2.6 million years ago (mya) at the end of the Pliocene. It is possible that "P. aethiopicus" evolved even earlier, up to 3.3 mya, on the expansive Kenyan floodplains of the time. The oldest "P. boisei" remains date to about 2.3 mya from Malema. The youngest record of "P. boisei" comes Olduvai Gorge (OH 80) about 1.34 mya; however, due a large gap in the hominin fossil record, "P. boisei" may have persisted until 1 mya. "P. boisei" changed remarkably little over its nearly 1 million year existence.