Sahelanthropus tchadensis is an extinct hominin discovered in Chad in 2001-2002. The fossils were discovered by Michel Brunet and colleagues, who are part of the Mission Paléoanthropologique Franco-Tchadienne (MPFT).
The species name literally means Sahel-man from Chad; Sahel is the name of the region where the fossils were found. Brunet and colleagues have nicknamed the fossil skull Toumaë (or Toumai), which means “hope of life” in the local Goran language.
The holotype (the specimen that illustrates the characters of the species) includes a nearly complete cranium and the other fossils include parts of two mandibles and some isolated teeth.
At the time of this writing, the fossils are still being analyzed; however, it is clearly a very important specimen for a number of reasons. First, at 6-7 million years old, the age of the specimen places it around the time of the common ancestor of humans and chimpanzees. The discoverers claim that it represents the oldest hominin discovered thus far—one very close to the root of the human family tree.
Second, if the Toumai fossils represent the oldest hominins, their discovery 2,700 km west of the Rift Valley in East Africa brings into question the longstanding theory that East Africa was the birthplace of hominins. This fossil, together with other early fossil hominins like Orrorin and Ardipithecus, suggests that early hominins in the late Miocene were geographically more widespread than previously thought. In addition, if Toumai proves to be bipedal, walking upright like humans, the mosaic environment associated with the fossils may also suggest that this key adaptation evolved before hominins moved onto the savanna.
Finally, the remarkably complete skull presents a unique combination of ape-like and human-like characters that make it particularly noteworthy. Although the brain is the size of a chimpanzee’s, the face is more human looking than hominins half its age. The human-like characters that link this specimen to other hominins include the small upper canine teeth, which are worn at the tips, and the intermediate thickness of the enamel in the premolars and molars. Aspects of the skull also align it with other, more recent, hominins. These include the size and shape of the foramen magnum (the hole in the base of the skull for the spinal cord) and a relatively flat face.
The relationship of Toumai to other fossil hominins and modern humans is currently unknown. It may represent a species that was a sister group of other hominins, or it could be part of the human lineage. There is even some controversy regarding whether or not the fossil actually represents a hominin. Perhaps the chief significance of this fossil is the finding of unsuspected diversity of early hominins. This suggests that there were likely many “experiments” with becoming human, some of which were more successful than others.
References:
- Brunet, M., Guy, F., Pilbeam, D., Mackaye, H., Likius, A., Ahounta, D., et al. (2002). A new hominid from the Upper Miocene of Chad, Central Africa. Nature, 418, 145-151.
- Wood, B. A. (2002). Hominid revelations from Chad. Nature, 418, 133-135.
