Sahelanthropus tchadensis is an extinct homininae species and is probably the ancestor to Orrorin that is dated to about , during the Miocene epoch, possibly very close to the time of the chimpanzee–human divergence. Few specimens other than the partial skull nicknamed Toumaï ("hope of life") are known.
Existing fossils include a relatively small cranium named Toumaï ("hope of life" in the local Daza language of Chad in central Africa), five pieces of jaw, and some teeth, making up a head that has a mixture of derived and primitive features. The braincase, being only 320 cm³ to 380 cm³ in volume, is similar to that of extant chimpanzees and is notably less than the approximate human volume of 1350 cm³.
The teeth, brow ridges, and facial structure differ markedly from those found in Homo sapiens. Cranial features show a flatter face, u-shaped dental arcade, small canines, an anterior foramen magnum, and heavy brow ridges. No postcranial remains have been recovered. The only known skull suffered a large amount of distortion during the time of fossilisation and discovery, as the cranium is dorsoventrally flattened, and the right side is depressed.
Sahelanthropus tchadensis may have walked on two legs. However, because no postcranial remains (i.e., bones below the skull) have been discovered, it is not known definitively whether Sahelanthropus was indeed bipedal, although claims for an anteriorly placed foramen magnum suggests that this may have been the case. Upon examination of the foramen magnum in the primary study, the lead author speculated that a bipedal gait "would not be unreasonable" based on basicranial morphology similar to more recent hominins. Some palaeontologists have disputed this interpretation, stating that the basicranium, as well as dentition and facial features, do not represent adaptations unique to the hominin clade, nor indicative of bipedalism; and stating that canine wear is similar to other Miocene apes. Further, according to recent information, what might be a femur of a hominid was also discovered near the cranium—but which has not been published nor accounted for.
Fifteen years after the discovery of the fossil, the anthropologist Roberto Macchiarelli  - professor at the University of Poitiers and the Museum of Natural History of Paris - suspects Michel Brunet and his laboratory in Poitiers of blocking information about a femur (potentially primate) found close to the skull . That the laboratory would have delayed identification may question the bipedalism of Toumaï.  ·  ·  ·  · .
The fossils were discovered in the Djurab Desert of Chad by a team of four led by a Frenchman, Alain Beauvilain, and three Chadians, Adoum Mahamat, Djimdoumalbaye Ahounta, and Gongdibé Fanoné, members of the Mission paleoanthropologique Franco-tchadienne led by Michel Brunet. All known material of Sahelanthropus was found between July 2001 and March 2002 at three sites: TM 247, TM 266, which yielded most of the material, including a cranium and a femur, and TM 292. The discoverers claimed that S. tchadensis is the oldest known human ancestor after the split of the human line from that of chimpanzees.
The bones were found far from most previous hominin fossil finds, which are from Eastern and Southern Africa. However, an Australopithecus bahrelghazali mandible was found in Chad by Mamelbaye Tomalta, Najia and Alain Beauvilain, Michel Brunet and Aladji H.E. Moutaye as early as 1995. With the sexual dimorphism known to have existed in early hominins, the difference between Ardipithecus and Sahelanthropus may not be large enough to warrant a separate species for the latter.