The most significant relic of this species is an upper femur that reveals indications of bone development typical of a biped, indicating that Orrorin tugenensis individuals likely walked upright on two legs while simultaneously climbing trees.
A hypothetical early Hominin species called Orrorin tugenensis was identified in 2000 and is thought to have existed between 6.1 and 5.7 million years ago. How Orrorin is connected to contemporary humans is unknown. Although this remains the most popular theory of human evolution as of 2012, its discovery was used to refute the idea that australopithecines are human forebears. The name of the only classified species, O. tugenensis, comes from the Tugen Hills in Kenya, where the first fossil was discovered in 2000. The name of the genus Orrorin (plural Orroriek) means "original man" in Tugen. Twenty fossils of the species have been discovered as of 2007.
