Sahelanthropus tchadensis

Sahelanthropus tchadensis Fossil range: Late Miocene
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Subfamily: Homininae Tribe: Hominini Subtribe: Hominina Genus: Sahelanthropus Brunet et al, 2002 Species: S. tchadensis
Binomial name
†Sahelanthropus tchadensis Brunet et al, 2002

Sahelanthropus tchadensis is a fossil hominid. From evidence at the fossil site in Chad in the African Sahel, it is thought to have lived about 7 million years ago.

The split of the line into humans and chimpanzees (known as human-chimpanzee divergence) probably happened between 6.3 and 5.4 million years ago. This can be seen from genetic data. Because the fossil is older than this spilt, its status is unclear. The first fossil found is known as Toumaï today.

Fossils

Some fossils, a cranium (skull), five pieces of jaw, and some teeth, make up a head that has features that are like both modern and primitive humans. The braincase is only 340 cm³ to 360 cm³ in volume, about the same as chimpanzees. It is much less than the human volume of about 1350 cm³.

The teeth and structure of the face are very different from Homo sapiens. The cranium found is damaged, it is very distorted, so no 3D computer reconstruction has been made. There are no bones other than parts of the skull. It is unknown if Sahelanthropus tchadensis was bipedal (walked on two legs). The placement of the foramen magnum suggests they were, though. Its canine wear is similar to other Miocene apes.

Relationship to modern humans and great apes

Sahelanthropus may be an ancestor of both humans and chimpanzees; no consensus has been reached yet by the scientific community. The difficulty is caused by its "mosaic of primitive and derived features". Probably it lived in semi-open woodland and savannah, rather than the rainforest of present-day apes.

Another possibility is that Toumaï is related to both humans and chimpanzees, but is the ancestor of neither. Brigitte Senut and Martin Pickford, the discoverers of Orrorin tugenensis, suggested that the features of S. tchadensis are consistent with a female proto-gorilla. Even if this claim is upheld, the find would still be significant, for at present few chimpanzee or gorilla ancestors have been found anywhere in Africa. Thus, if S. tchadensis is an ancestral relative of the chimpanzees (or gorillas), it represents the first known member of their lineage.

Furthermore, S. tchadensis does indicate that the last common ancestor of humans and chimpanzees is unlikely to resemble chimpanzees very much, as had been previously supposed by some paleontologists.

The fauna found at the site suggest an age of more than 6 million years, as these species were probably extinct already by that time.

Related pages

• Human evolution

References

• Brunet, Michel; et al. (2002). "A new hominid from the Upper Miocene of Chad, Central Africa". Nature 418: 145–151. doi:10.1038/nature00879. 
• Brunet, Michel; et al. (2005). "New material of the earliest hominid from the Upper Miocene of Chad". Nature 434: 752–755. doi:10.1038/nature03392. 
• Guy, Franck; et al. (2005). "Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium". Proceedings of the National Academy of Science 102 (52): 18836–18841. 
• Wolpoff, M. H.; et al. (2006). "An Ape or the Ape: Is the Toumaï Cranium TM 266 a Hominid?". PaleoAnthropology 2006: 36–50. http://www.paleoanthro.org/journal/content/PA20060036.pdf. 

Other websites

Look up Sahelanthropus in Wikispecies, a directory of species

• Sahelanthropus.com
• http://toumai.site.voila.fr/
• Fossil Hominids: Toumai
• National Geographic: Skull Fossil Opens Window Into Early Period of Human Origins
• image of the skull (nature.com)
• New Findings Bolster Case for Ancient Human Ancestor