Sahelanthropus: The femur of Toumaï?

Note: This post was published in 2009. I have left the original post as a piece of news reflecting the time it was published. In more recent years, the story of the femur discussed in this post and other postcranial fossils attributed to Sahelanthropus tchadensis has gone through several twists and turns, as noted in the notes at the end of the post.

Some weeks ago, I wrote about an article by Alain Beauvilain and Jean-Pierre Watté, in my post, “Did somebody bury the bones of Toumaï?” If you missed that post, go back and read it – it gives some essential background.

I ended the post with this little observation:

Toumaï's skull was found alongside a femur.

I imagine that a majority of paleoanthropologists have heard that the faunal collection from Toros-Menalla includes a primate femur of the right approximate size to match the Toumaï skull. Probably only very few knew that this femur may have been found in the immediate locality of the skull. Still, a lot of them must be wondering: If there are possible postcranial remains of Sahelanthropus, wouldn't they be the most important test of whether the species is the first hominid?

Now, thanks to a story in the July print issue of the French science magazine La Recherche (“Le fémur de Toumaï”) along with some valued correspondence from readers, it's possible for me to give some more details.

The La Recherche story, reported by Nicolas Constans, includes a quote from Aude Bergeret, a former student at Poitiers, and now director of the Musée de la Haute-Auvergne. I want to give my translation of the story's first two paragraphs, which pose the obvious question:

The femur of Toumaï

Eight years after the discovery of the skull of the oldest known hominid, an unedited photo shows that a femur of the same species was found simultaneously. Why hasn't it been published?

The skull of Toumaï is considered by many paleontologists as that of the oldest known hominid, Sahelanthropus tchadensis. The position of the hole connecting its vertebral column indicates that it was probably a biped. But to know how it walked would require one of the bones of the leg. Unfortunately, none were found at the site, as stated in 2002 by the CNRS. However, a photograph from the day of the discovery has now been published in a Normandy review (pictured above). It shows the skull posed on the sand next to a bone, designated as the femur of a hominid. What many paleontologists privately confided for several years is from now on in the public square. Why did this announcement not follow the normal publication channels?

Well, this may not be such a mystery. We all know that there's no urgency whatsoever in the publication of early hominid remains. Fifteen, twenty years, however long it takes for preparation and analysis, it's no problem. Hey, just look what happens when you publish your early hominid femur quickly, complete with CT scans, like the Lukeino hominids. You get all kinds of sniping from other early hominid excavators, about how you really did everything wrong and can't even read a CT. It's a wonder any of them are willing to publish anything at all.

Still, the story in this case took several interesting turns. Some of them were detailed in my earlier post on the paper by Beauvilain and Watté. Those have to do with the discovery itself and alleged inaccuracies in subsequent descriptions of the discovery in scientific journals.

A different twist to the story is what happened after the discovery, during the study of the faunal remains in Poitiers. The femur figures into the story of the discovery, because Beauvilain's pictures put it at the scene. But it is in other respects a separate issue, and I don't think it helps to confuse them with each other.

The femur

Here are two photographs of the femur, kindly provided to me by Aude Bergeret.

By Bergeret's account (and corroborated by other sources), the femur lay unrecognized in the Toros-Menalla faunal collection for almost three years after the discovery. Again, from the La Recherche article (my translation):

[I]s the bone in the photo really the femur of a hominid? And why wasn't it published along with the skull? According to Aude Bergeret, today director of the Musée de la Haute-Auvergne, in Saint-Flour, who in 2004 carried out research in Michel Brunet's Poitiers laboratory, it is because it had not been identified by the beginning of 2004. At that time, when she was studying the fossilization of animal bones found at the Toumaï site, she solicited the opinion of one of her professors on this subject, who addressed it: "During the conversation, he saw that the bone, the species of which had not yet been determined, was not the femur of an ordinary animal, but that of a hominid. Then he alerted a researcher in the laboratory. This bone, which I had many times in my hands, is indeed that figured in the photograph."

Students of anatomy will see that this femur shaft is not a super-obvious case. It lacks the distal end, the head and most of the neck. Still, from these photos the diaphyseal anatomy looks like it could be a hominoid. I would assume that Bergeret and the professor mentioned were able to make the ID with some confidence, given the opportunity to examine it along with a comparative collection.

But as to the question of whether the femur represents a biped; that's more difficult. Most of the readily diagnostic features are missing. The remaining parts are hard to evaluate -- for example, does it have an intertrochanteric groove? That's very important to the diagnosis, and it can't really be evaluated from a photo. There might be some evidence in the cortical bone distribution at the neck, but the break is distal to the point where you'd really want to look. I don't think you could get a valid comparison of superior and inferior cortical thicknesses based on what remains. In any event, I wouldn't hazard a public guess about whether it's a biped without examining the specimen.

I will say this: Based only on the preserved anatomy, it will be more difficult to make a case that this femur is a biped than it was for Orrorin. That's not to say it's a biped or not; just to say that whoever publishes on it will have a debate on their hands.

The association

Is the femur associated with the skull? Beauvilain's picture shows them within a meter of each other.

If the account in Beauvilain and Watté (2009) is correct, then their association could hardly be closer. The article in La Recherche cites the fossils' discoverer:

The discoverer of Toumaï, Ahounta Djimdoumalbaye, contests this version: "This photograph cannot have been made until after 11 o'clock, when Alain Beauvilain, who worked with another party at the site, rejoined us, my colleague Fanoné Gongdibé (deceased in 2007) and me. It shows the bones that we had found in the morning and assembled on the sand. The skull was not discovered like this, but blocked in concretions."

That quote doesn't really contradict the other account of the photograph, as Beauvilain and Watté (2009) describe the skull as having clearly been moved. The extent that the other bones may have been moved is not so clear. Beauvilain and Watté seem to have anticipated this explanation (that the bones were placed in the pictured positions by the discoverers, not found that way), as they took pains to note the lack of footprints or other marks around the bones (only on one side) and the effects of windblown sand immediately shadowing them. They argue that the bones had been in that position for a long time.

Even if Beauvilain's photo shows the bones as they were discovered, that doesn't necessarily mean that the femur and skull were deposited at the same time or exact location. The accumulation of different fossils into a small area might have happened as wind erosion scooped material away from them, changing the local topography (aeolian deflation). Close association at the site may therefore not mean much about original deposition. Plus, there remains Beauvilain and Watté's hypothesis that somebody transported and reburied the remains in the past. (I should also mention that least one reader has written to me, on the basis of knowledge of the local nomads, to express doubt about this hypothesis.)

So, it's completely unclear whether the femur and skull may represent a single individual. On the broader question of whether they represent a single species of ancient primate, we can at least observe that the femur is around the right size for the skull. It seems unlikely that two similar-sized hominoid species both lived in the same area during the limited time span represented by the stratigraphy. But I guess we have to wait and see what else may turn up in the faunal collection....

What's going on now?

None of my sources know what has happened to the bone since 2004, or what kinds of analyses may have been conducted on it. I've expected some publication on the femur for several years now (a reference to it can be found in my predictions for 2006).

Multiple sources corroborate the story that the femur was not recognized at the time of discovery or afterward. After its identification, its relevance to testing locomotor and phylogenetic hypotheses about Sahelanthropus would have been obvious to anyone. Unfortunately, we'll just have to wait.

La Recherche asked the leader of the Sahelanthropus discovery project, Michel Brunet. Here is his response (original followed by my translation):

Au Tchad, nous avons mis au jour des milliers d'ossements, qui sont en cours d'étude. Peut-être s'y trouve-t-il des os d'hominidés, mais je ne comment que ce qui a été publié dans une revue scientifique.

In Chad, we have uncovered thousands of bones, which are in the process of study. Perhaps among them are hominid bones, but I only comment on those that have been published in a scientific review.

I think this is perfectly legitimate response -- don't comment on scientific subjects until you're ready for the sun to shine on them.

Still, we have a pretty good idea of how many of those thousands of bones were found close to the Toumaï skull:

Some ideas need more sunshine than others.

Note: For readers interested in follow-ups to this post, I wrote again in 2018 when the femur was once again in the news, this time because Macchiarelli and Bergeret were blocked from presenting their research on the femur at a conference: “What's the deal with the Sahelanthropus femur?”

Ultimately, a description of this femur was published by Roberto Machiarelli and coworkers in 2020, followed by a report by Daver and collaborators in 2022 and a subsequent analysis by Marine Casenave and collaborators in 2024. While the femur has a few features that overlap with some later hominins, for the most part it resembles femora of non-bipedal primates. Many researchers have questioned the evidence for habitual bipedal stance and gait in Sahelanthropus based on the evidence from this bone.

References

Beauvilain A, Watté J-P. (2009). Toumaï (Sahelanthropus tchadensis) a-t-il été inhumé? Bulletin de la Société Géologique de Normandie et des Amis du Muséum du Havre 96:19-26.

Constans, Nicolas. (2009). Le fémur de Toumaï. Le Recherche 432. https://www.larecherche.fr/le-fémur-de-toumaï