Sahelanthropus tchadensis dating techniques
is a hominin species dating to between 4.5 and 4.2 million years ago (mya) using paleomagnetic and radioisotopic dating methods.(Paleomagnetic uses periodic reversals in the Earth’s magnetic field; radioisotopic utilizes the known rate of decay of one radioisotope into another) Importantly, is the best evidence discovered thus far for the root of the hominin family tree.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.Fragmentary radii and ulnae (lower arm bones; ‘radii’ is the plural of ‘radius.’ the bone on the outside of the lower arm; ‘ulnae’ is the plural of ‘ulna,’ the bone on the inside of the lower arm ) are also represented and possess features not exhibited by living African apes.For example, the part of the ulna that connects with the humerus faces forward, unlike that of African apes, which faces upward.Paleoanthropologists are also interested in demonstrates that great ape adaptations for forelimb suspension and knuckle-walking were not present in the last common ancestor of hominins.This argument also implies that living great apes evolved suspensory adaptations separately and that none is a good model of the anatomy and behavior of the last common ancestor of chimpanzees and humans.
This combination of traits is important because scientists have long considered obligate bipedality to be a defining characteristic of the hominin lineage.
Fossils of this species, found in the Middle Awash region and the site of Gona in Ethiopia, possess derived features (features different from those found in the ancestor) in the skull and teeth.
The postcranial skeleton of , however, suggests this species had not evolved obligate bipedality ("obligate" means the skeletal anatomy limits locomotion to one means, in this case bipedality.
Interestingly, in contrast to its hominin-like ilium, the wrist was mobile (like that on living monkeys).
The shape and size of the ischium suggest that the hamstring muscles were well-developed, a condition seen in living primates that emphasize climbing in their locomotor behaviors.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; 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.