The Elements of Evolution (56) Orrorin


Orrorin tugenensis (“original man of the Tugen hills”) (6.2–5.6 MYA) presaged later hominids. The thickness of a found femur (thigh bone), as well as its hip socket, identifies Orrorin as bipedal, though the orientation and shape of the toe suggest a grasping foot. The shapes of the upper arm bone and slightly curved finger bone intimates that the upper arms were weight-bearing. Orrorin looks to have been a tree climber as well as walking upright.

Found teeth suggest a diet of fruit and seeds: large upper front teeth, reduced apelike pointed canines, microdont (smaller) post-canines like modern humans, and low cusped molars.

The location of fossils found indicate that Orrorin lived in dry evergreen forests, lakeside woodlands, and wet grasslands – not the savanna long assumed as the progenitor environment of hominins.

Orrorin arose 3 MYA earlier than Australopithecus afarensis, but Orrorin‘s anatomy is closer to modern humans. For one, Orrorin‘s hand indicates a precision grip, more capable of fine manipulation than many later hominids.

If Orrorin is the ancestor to modern humans, australopiths may be a side branch of the hominin tree. The lineage to humans remains unclear and contentious.