Sahelanthropus is an Extinction genus of Hominidae dated to about during the Late Miocene. The type species, Sahelanthropus tchadensis, was first announced in 2002, based mainly on a partial cranium, nicknamed Toumaï, discovered in northern Chad.
The definitive phylogenetic position of Sahelanthropus within hominids is uncertain. It was initially described as a possible hominin ancestral to both and , but subsequent interpretations suggest that it could be an early member of the tribe Gorillini or a stem-hominid outside the hominins. Examinations on the postcranial skeleton of Sahelanthropus also indicated that this taxon was not a habitual biped.
The skull was nicknamed Toumaï by the then-president of the Republic of Chad, Idriss Déby, not only because it designates in the local Daza language meaning "hope of life", given to infants born just before the dry season and who, therefore, have fairly limited chances of survival, but also to celebrate the memory of one of his comrades-in-arms, living in the north of the country where the fossil was discovered, and killed fighting to overthrow President Hissène Habré supported by France. The skull discovered in Chad bears the name of a comrade of the Chadian president who died in combat Dispatch of Associated Press, Denver, July 11, 2002. Toumaï also became a source of national pride, and Brunet announced the discovery before the Ministry of Foreign Affairs and a television audience in the capital of N'Djamena, " l'ancêtre de l'humanité est Tchadien...Le berceau de l'humanité se trouve au Tchad. Toumaï est votre ancêtre" ("The ancestor of humanity is Chadian...The cradle of humanity is in Chad. Toumaï is your ancestor."). N'Djamena, Conference of July 10, 2002, at 1h 0' 30"
Toumaï had been found with a femur, but this was stored with animal bones and shipped to the University of Poitiers in 2003, where it was stumbled upon by graduate student Aude Bergeret the next year. She took the bone to the head of the Department of Geosciences, Roberto Macchiarelli, who considered it to be inconsistent with contra what Brunet et al. had earlier stated in their description analysing only the distorted skull. This was conspicuous because Brunet and his team had already explicitly stated Toumaï was associated with no limb bones, which could have proven or disproven their conclusions of locomotion. Because Brunet had declined to comment on the subject, Macchiarelli and Bergeret petitioned to present their preliminary findings during an annual conference organised by the Anthropological Society of Paris, which would be held at Poitiers that year. This was rejected as they had not formally published their findings yet. They were able to publish a full description in 2020, and concluded Sahelanthropus was not bipedal.
In 2022, French primatologist Franck Guy and colleagues reported that a hominin left femur (TM 266-01-063), a right (TM 266-01-358), and a left (TM 266-01-050) ulna (forearm bone) were also discovered at the site in 2001, but were excluded originally from Sahelanthropus because they could not be reliably associated with the skull. They decided to include it because Sahelanthropus is the only hominin known from the site, and they concluded that the material is consistent with obligate bipedalism, the earliest evidence of such. In 2023, Meyer and colleagues suggested that its phylogenetic position and its status as a hominin still remain equivocal.
All Sahelanthropus specimens, representing six to nine different adults, have been recovered within the area.
Their methods were soon challenged by Beauvilain, who clarified that Toumaï was found on loose sediments at the surface rather than being "unearthed", and had probably been exposed to the harsh sun and wind for some time considering it was encrusted in an iron shell and desert varnish. This would mean it is unsafe to assume that the skull and nearby sediments were deposited at the same time, making such radiometric dating impossible. Further, the Sahelanthropus fossils lack white silicon cement which is present on every other fossil in the site, which would mean they date to different time periods. Because the large mammal fossils were scattered across the area instead of concentrated like the Sahelanthropus fossils, the discoverers originally believed the Sahelanthropus fossils were dumped there by a palaeontologist or geologist, but later dismissed this because the skull was too complete to have been thrown away like that. In 2009, Alain Beauvilain and argued that Toumaï was purposefully buried in a "grave", because the skull was also found with two parallel rows of large mammal fossils, seemingly forming a box. Because the "grave" is orientated in a northeast–southwest direction towards Mecca, and all sides of the skull were exposed to the wind and were eroded (meaning the skull had somehow turned), they argued that Toumaï was first buried by nomads who identified the skull as human and collected nearby limb fossils (believing them to belong with the skull) and buried them, and was reburied again sometime after the 11th century by Muslims who reorientated the grave towards Mecca when the fossils were re-exposed.
A further possibility is that Toumaï is not ancestral to either humans or chimpanzees at all, but rather an early representative of the Gorillini lineage. 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 lose none of its significance, because at present very few chimpanzee or gorilla ancestors have been found anywhere in Africa. Thus, if S. tchadensis is an ancestral relative of the chimpanzees or gorillas, then it represents the earliest known member of their lineage. S. tchadensis does indicate that the last common ancestor of humans and chimpanzees is unlikely to closely resemble extant chimpanzees, as had been previously supposed by some paleontologists. Additionally, with the significant sexual dimorphism known to have existed in early hominins, the difference between Ardipithecus and Sahelanthropus may not be large enough to warrant a separate genus for the latter.
The teeth, brow ridges, and facial structure differ markedly from those found in modern humans. Cranial features show a flatter face, U-shaped tooth rows, small Canine tooth, an anterior foramen magnum, and heavy brow ridges. 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.
In 2020, the femur had been formally described, and the study concluded it was not consistent with habitual bipedalism. But, in 2022, Daver and colleagues suggested that the ulnar and femoral morphologies do show characteristics consistent with habitual bipedalism. In 2023, however, Meyer and colleagues examined its ulna shaft and argued that Sahelanthropus is not an obligate biped based on the mathematical analysis of its locomotor behavior which indicated that its forelimbs had different functions compared to modern humans and hominins, and that it probably knuckle-walking like modern gorillas and chimpanzees, so more examination is required to truly identify its locomotor behavior (i.e. whether it exhibited facultative bipedalism) and its phylogenetic position as a hominin in the evolution of humans. A 2024 study re-examined the 2022 study's postcranial evidence, and concluded that it is not sufficient to determine whether Sahelanthropus was a habitual biped, since none of the features are consistent with or unique to bipedal hominins, but with non-hominin apes or even non-primates.
Locomotion
Palaeoecology
See also
Further reading
External links
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