Kate Wong has been reporting from the Paleoanthropology Society meetings in Honolulu. Today she describes a presentation about the endocast shape of the Toumaï skull, Sahelanthropus tchadensis: “Brain Shape Confirms Controversial Fossil as Oldest Human Ancestor”.
Toumaï has been claimed to be the earliest member of the hominin lineage, although I and some other paleoanthropologists have disagreed with this interpretation.
The resulting virtual reconstruction of the endocast reveals that Touma had a cranial capacity of 378 cubic centimetersconsistent with earlier estimates. This puts it within the range of chimp cranial capacity. In comparison, modern humans have brains around three times larger than that. But though Toumas brain was apelike in its small size, it was apparently homininlike in other ways. In a presentation given on April 2 at the annual meeting of the Paleoanthropology Society, Bienvenu reported that the endocast shows strongly posteriorly projecting occipital lobes, a tilted brainstem, and a laterally expanded prefrontal cortex, among other hominin brain characteristics.
A “laterally expanded prefrontal cortex” has been a recurring argument for changes in brain organization in hominin endocasts across a range of geological ages. Understanding when and how this area really changed in our evolution will be very useful.