On September 10, 2020, the scientific community learned that on July 19, 2001, the CNAR team (National Center for Research Support of the Chadian Ministry of Higher Education) had unearthed not only the head (a skull and a mandible, this one still not being published) but also a femoral shaft and a partial left ulna (ulna) of a Sahelanthopus tchadensis.
She also learned that during the next mission, in October 2001, she had found a second right partial ulna. A similarity in size and shape for the common parts allows us to estimate that these ulnae belonged to the same individual.
The announcement is made in a pre-article by researchers from the Paleontology Laboratory at the University of Poitiers and Chadian scientists.
This is a very big announcement as it helps to refine the understanding of the fossils collected. It is also a great satisfaction for those who have done most of the fieldwork, even if the editors of the article thought it interesting to multiply unfounded criticisms of them.
The first fossils were found in close proximity to each other, as their inventory numbers indicate (TM266-01-60 for the head, TM266-01-63 for the femoral shaft, TM266-01-50 for the first ulna, a left ulna.The second ulna, TM266-01-358, on the right, was close since it had been collected from the first return to the field in October 2001.
To situate the circumstances, in July 2001, the site of TM266 was discovered on the last day of a mission which had scheduled to reach this sector at the end of the route. Reserves of water and fuel, and fatigue, made it impossible to extend the stay any further without jeopardizing the safety of a totally isolated group in the middle of an erg.
If an ancient human intervention, at an undefined date, had not moved the Sahelanthropus fossils, the CNAR team might have been able to find these fossils in almost anatomical connection as it has discovered so many others in this situation. Due to the context of the fossiliferous sites, vast flat sandstone expanses traversed by dunes and overlapping in episodes with a thick sandy mantle before the wind clears these sandstone surfaces again, it is quite possible to find other Sahelanthropus in anatomical connection. It almost succeeded in July 2001 but an anonymous hand having recently moved the Sahelanthropus fossils, such an update remains to be realized.
The fossiliferous area is immense, this challenge is realistic. Since January 2001, with the discovery of a young hippopotamus in connection and in situ, the CNAR team was convinced to be able to find a hominid under the same conditions. Indeed, while the previous fossils in connection concerned large mammals (elephants, hippos), we had here a fossil of "hominid size", two meters in all).
The first article, which has not yet received peer validation, presents Sahelanthropus as a perfect biped.
A few days later, on September 30, 2020, the final version of an article presented in 2019 to the international professional journal of paleoanthropologists appeared. Its initiator, Roberto Macchiarelli (University of Poitiers and National Museum of Natural History of Paris) was recruited in May 2001 by the Paleontology laboratory of the University of Poitiers in order to provide his expertise in the event of an update of possible postcranial remains of hominoids brought back from the Chadian desert. He was assisted by Bernard Wood (Georges Washington University, USA), Marchi (universities of Pisa, Italy, and Witwattersrand, Republic of South Africa) and Aude Bergeret-Modina, director of the Montauban Museum (France), who had made the mistake, fatal for his career as a paleotonlogue, to report the diaphysis to Professor Macchiarelli before undertaking the programmed destruction of the fossil for scientific purposes as the authorization had been given to him. This article does not present Sahelanthropus as a bipedal.
In 2002, when the discovery of Sahelanthropus tchadensis was announced by the journal Nature, it was Bernard Wood (Nature, Vol 418, 11 July 2002, pp 133-135),
who wrote the introductory pages of presentation and implications of this discovery comparing it by its importance to that of the 'child of Taung' in 1925. It is a discovery that can only be compared to that of the skull of Taung, the first Australopithecus exhumed, in 1924, by Raimond Dart and which was to demonstrate ¬as predicted by Darwin ¬ that our origins were African. He nevertheless specifies “What is remarkable about the chimpsized cranium TM 266-01-060-1 discovered by Brunet et al. is its mosaic nature. Put simply, from the back it looks like a chimpanzee, whereas from the front it could pass for a 1.75-million-year-old advanced australopith".
Abstract : Terrestrial bipedal locomotion is one of the key adaptations defining the hominin clade. Evidences of undisputed bipedalism are known from postcranial remains of late Miocène hominins as soon as 6 Ma in eastern Africa. Bipedality of Sahelanthropus tchadensis was hitherto documented at 7 Ma in central Africa (Chad) by cranial evidence. Here, we present the first postcranial evidence of the locomotor behavior of the Chadian hominin with new insights on bipedalism at the early stage of our evolutionary history. The original material was discovered at locality TM 266 (Toros-Menalla fossiliferous area), and consists in one left femur and two antimeric ulnae. These new findings confirm that hominins were already terrestrail biped relatively soon after the human-chimpanzee divergence but also suggest that careful climbing arboreal behaviors was still a significant part of their locomotor repertoire.
Roberto Macchiarelli R., Bergeret-Medina A., Marchi D., Bernard Wood B.
Article history : received 11 December 2019, accepted 30 September 2020.
abstract : A partial left femur (TM 266-01-063) was recovered in July 2001 at Toros-Menalla, Chad, at the same fossiliferous location as the late Miocene holotype of Sahelanthropus tchadensis (the cranium TM 266-01-060-1). It was recognized as a probable primate femur in 2004 when one of the authors was undertaking a taphonomic survey of the fossil assemblages from Toros-Menalla. We are confident the TM 266 femoral shaft belongs to a hominid. It could sample a hominid hitherto unrepresented at Toros-Menalla, but a more parsimonious working hypothesis is that it belongs to S. tchadensis. The differences between TM 266 and the late Miocene Orrorin tugenensis partial femur BAR 1002000, from Kenya, are consistent with maintaining at least a species-level distinction between S. tchadensis and O. tugenensis. The results of our preliminary functional analysis suggest the TM 266 femoral shaft belongs to an individual that was not habitually bipedal, something that should be taken into account when considering the relationships of S. tchadensis. The circumstances of its discovery should encourage researchers to check to see whether there is more postcranial evidence of S. tchadensis among the fossils recovered from Toros-Menalla.
What does the international press say ?
18 Novembre 2020, by Michael Marsh
AFTER more than a decade in limbo, a crucial fossil of an early human relative has finally been scientifically described. The leg bone suggests that Sahelanthropus tchadensis, the earliest species generally regarded as an early human, or hominin, didn’t walk on two legs, and therefore may not have been a hominin at all, but rather was more closely related to other apes like chimps.
A paper from a rival group, not yet peer-reviewed, disputes this. The studies are the latest twist in a bitter saga that has seen the fossil held back from publication and its existence ignored.
“We have been anxiously awaiting the publication of this femur for many years,” says Kelsey Pugh at the American Museum of Natural History in New York.
Michel Brunet from the University of Poitiers in France and his colleagues discovered the remains of Sahelanthropus tchadensis in Chad in 2001. The team described a skull, dubbed Toumaï, plus fragments of lower jaw and some teeth (Nature).
Brunet and his colleagues have always maintained that Sahelanthropus habitually walked on two legs – like modern humans but unlike chimpanzees and other apes. This was based on an analysis of the base of the skull, suggesting that the spine was held upright. Many other researchers have argued that this isn’t sufficient evidence for bipedality.
Resolving this is key, because the Sahelanthropus bones are believed to be 7 million years old, far older than other human relatives like Australopithecus. If it was a biped, that would make it the oldest known hominin. If not, it may not be that closely related to us.
The researchers found a femur, or thigh bone, along with two ulnas, or forearm bones, that would help clarify the matter, but they published nothing about them for almost two decades, prompting criticism from colleagues. Brunet didn’t respond to a request for comment from New Scientist.
The bones were brought to the University of Poitiers. There, Aude Bergeret-Medina, who discussed the bones with one of her tutors, Roberto Macchiarelli, identified a long, unlabelled bone as a femur, probably from a primate, in 2004.
Bergeret-Medina had been given permission by her superiors to cut the femur into pieces, but she became uneasy about doing this. Macchiarelli examined it and advised her to wait until this could be checked with Brunet and his team, most of whom were in Chad.
Later, Bergeret-Medina was unable to find the femur. Neither she nor Macchiarelli ever saw it again. However, when Brunet’s team didn’t describe the femur, she and Macchiarelli prepared a study using her photos and measurements.
She and her colleagues first tried to present their findings at a 2018 conference in Poitiers, but the presentation was rejected by the organisers. In late 2019, they submitted a paper that has now been published (Journal of Human Evolution).
Bergeret-Medina’s team argues that the femur isn’t that of a bipedal animal. “There are a lot of indicators which deeply discourage bipedal gait,” says Macchiarelli. In particular, the bone is curved, not straight, typical of apes like chimps.
However, a second study, posted on a Nature Research journals preprint server, disputes this, though it has not yet passed peer review. Its lead author is Franck Guy at the University of Poitiers, a co-author on the original Sahelanthropus paper, who declined to comment.
Guy and his colleagues say the femur does show signs of bipedality. For instance, it has a hard ridge near the top, which they say would support an upright body. Macchiarelli declined to comment on the paper, but shared with New Scientist a copy of a letter he sent to Nature detailing claimed inaccuracies.
Other palaeoanthropologists agree with the analysis by Bergeret-Medina’s team. “The shape of the femur and general morphology doesn’t look like a biped to me,” says Brigitte Senut at the National Museum of Natural History in Paris, France.
And Madelaine Böhme at the University of Tübingen in Germany says: “I saw the pictures 10 or 12 years ago, and it was clear to me that it’s more similar to a chimp than to any other hominin.”
It remains unclear when and where bipedalism first evolved, says Böhme. Another African species, Orrorin tugenensis, lived 6 million years ago and has clear signs of bipedality. But prior to that, most apes lived in Eurasia, not Africa, and she has found tentative evidence that bipedality emerged there.