Taumai’s thighbone was that of a bipedal, square-shaped tree

Représentation de Toumaï bipède arboricole

A definitive new analysis of Toumaï confirms that he was bipedal. But not only … publication In review Nature Analysis of one or more femur bones and two wrist bones Sahelanthropus tichadensis (scientific name of Toumaï), a survey conducted in Chad 7 million years ago, first testifies that these primates walked upright on their two legs. Although their bipedalism wasn’t exclusive and didn’t resemble ours, this meticulous work shows that this hominin fit right in with the pre-human lineage! “This study reinforces the idea of ​​a bipedalism achieved very early in our history, but still associated with the possibility of locomotion on four limbs in trees. Explain the authors of this study, which includes researchers from the CNRS, the University of Poiriers and their Chadian partners.

Old controversies surround bipedalism

The acquisition of bipedalism is considered a critical step in human evolution. “even though, Due to the paucity of ancient fossils, the mechanisms and date of emergence of this movement are hotly debated.“, CNRS explains in a press release. The skull of Sahelanthropus tichadensis, discovered by the Franco-Chad Paleoanthropological Mission (MPFT) in Chad in 2001 at Toros-Menalla in the Djourab Desert (Chad), has already suggested a bipedal station. In particular the orientation and anterior position of the foramen magnum, where the vertebral column is attached, suggests a bipedal locomotion, supporting bipedalism. However, other paleontologists saw Touma as a protogorilla Its status as the oldest representative of the human race has sometimes been debated.

Left image: from left to right, femur, in posterior and medial view, right and left ulna (cubitus), in anterior and lateral view. Right image: Example of analysis performed for the interpretation of the locomotor mode of Sahelanthropus tichadensis. 3D cortical thickness variation map for the femurs of modern human, chimpanzee, gorilla (left to right) and Sahelanthropus. This analysis helps to understand the variations of mechanical stresses in the femur and to interpret these stresses in terms of locomotor mode.

A femur whose publication was eagerly awaited

But in addition to the skull, jaws, and teeth fragments nicknamed Toumai that have been the subject of publications, the Toros-Menella region has yielded two. Ulna (or ulna, wrist bone) a femur (femur) (See the image above). These bones are attributed to Sahelanthropus As no other large primates have been found at the site. However, it is impossible to know whether they belong to the same individual as the skull. By publishing an analysis of these precious remains, paleontologists Frank Guy and Guillaume Dever and their colleagues at the University of Poitiers concluded. A detailed analysis of the femur in particular led to a controversy that lasted more than a decade.

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and femur Ulna They were subjected to measurements and analyzes regarding their external morphology and internal structure imaged by microtomography: biometric measurements, morphometry and biomechanical indicators. Great ape specimens: chimpanzees, gorillas, orangutans, Miocene apes, and members of the human group (Ororin, ArdipithecusAustralopithecus, Homo old, A wise man).

He didn’t walk like a gorilla

The structure of the femur indicates that Sahelanthropus Usually bipedal for walking on the ground, but possibly also in trees. Accordingly Ulna, this bipedalism was held together in a quadrangular environment assured by the firm grips of the hands, distinctly different from the resting of the phalanges on the backs of gorillas and chimpanzees. But without the wrist and arm bones Sahelanthropus tichadensis, what factors led to the hypothesis that they moved quadrupedally with firm grips and not on folded joints (knuckle walking) like gorillas? “This is not knuckle-walking because the olecranon (the proximal part of the ulna that forms the elbow) remains upright as in humans and does not turn backward as in chimpanzees and gorillas.“, authors reply to Science et Avenir. The hand and wrist flexor muscles at the olecranon also lack a tubercle (protuberance) similar to knuckle-walkers, which helps stabilize their hand when pressed against the back of the second phalanges. Elbow joint Sahelanthropus was particularly stable, held by strong flexor muscles of the fingers, indicating a particularly firm grip. Arboreal quadrupedalism shows biomechanical indicators of the ulna that resemble those of more primitive Miocene forms.”

The conclusions of the study, especially the identification of habitual bipedalism, are based on the observation and comparison of the femur and more than twenty characteristics. Ulna. They are the most imaginative interpretation of this combination of characters. All these data support the idea of ​​bipedal locomotion early in human history, although other modes of locomotion were also practiced at this point.

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Humans diverged from the chimpanzee group during the late Miocene, probably between 10 Ma (millions of years before today) and 7 Ma.  This divergence resulted in very different morphologies: the bones of the limbs, for example, present differences associated with quadrupedal movement.  Chimpanzees and bipedalism to modern humans.  Credit: © Frank Guy / Paleoprim / CNRS - University of Poitiers

Humans diverged from the chimpanzee group during the late Miocene, probably between 10 Ma (millions of years before today) and 7 Ma. This divergence resulted in very different morphologies: the bones of the limbs, for example, present differences associated with quadrupedal movement. Chimpanzees and bipedalism to modern humans.

This work benefited in particular from the support of the Ministry of Europe, the Ministry of Foreign Affairs, the Chadian State, the ANR, the Nouvelle-Aquitaine Region, the CNRS, the University of Poitiers and the French delegation in Chad. It is dedicated to the memory of the late Yves Coppens, a pioneer and inspiration for MPFT’s work in the Djourab desert.

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