The femur of Orrorin tugenensis, one of the oldest early humans is shaped in between that of extinct apes and other early hominins reports a paper published in Nature Communications this week. The work shows that Orrorin tugenensis has a unique combination of both Miocene ape and early hominin features, consistent with the view that it was one of the earliest species to walk on two feet. These findings could therefore have implications for understanding the origins of human bipedalism.
The fossil record indicates that the earliest hominins were primitive bipeds that evolved from an African Miocene ape about 6 million years ago. Because both humans and living great apes have been evolving along different paths for a long time, it is unclear what the last common ancestor to living apes and humans looked like. Sergio Almecija and colleagues now suggest that Orrorin tugenensis -- an early hominin who climbed trees but also likely walked upright -- may provide us with clues. The team used 3D geometric morphometric analyses to compare femoral shape variation between living great apes and humans, as well as fossils of Miocene apes and early hominins, including Orrorin tugenensis. They show that the femora of modern humans and living great apes evolved in different directions from a more primitive shape shown in some fossil apes and that Orrorin combines features of both Miocene apes and early hominins.