Toumai: reverse-engineering a human ancestor

Abstract

French anthropologists led by Michel Brunet from the University of Poitiers found only one specimen of Sahelanthropus tchadensis in Chad; they named him Toumai because the word means "hope of life" in the local language. Toumai's uniqueness made him important to anthropology as a whole, but it also made him very difficult to analyze. Anthropologists suspected that Toumai and the rest of his species - dubbed Sahelanthropus tchadensis - walked upright from the moment they unearthed his skull in central Africa in 2001. But the skull had been crushed, pressed flat, and stretched out by the rock that surrounded it. To prove whether this new species was truly one of us, scientists had to do more than just reassemble it. They had to reverse-engineer the skull back into its original shape - using virtual reality. While Brunet returned to Chad to find more physical evidence to backup his claim, some of his colleagues turned to computer science to better assess Toumai's skull. Christoph Zollikofer and Marcia Ponce de Leon from the University of Zurich-Irchel in Switzerland performed a morphometric analysis, using computer software to reconstruct the skull and return it to its original shape. They'd been performing similar analyses on Neanderthal skulls since the early 1990s. They started by recording a high-resolution computed tomography (CT) scan of the skull fragments. CT scans are essentially X-ray images in 3D, and CT scanners are standard equipment in hospitals because they let doctors view soft tissue and bone structures inside the body. For Toumai, they used an industrial tomography machine, which is normally reserved for materials testing, because the fossil was too dense for a medical scanner. The team used data-segmentation techniques to digitally separate remaining bits of sediment rock from the bone fragments and the fragments from each other. They then used mophometric algorithms to detect both how the fragments had been deformed and how to "undo" the deformation.