7 million years old – new secrets of the oldest representative of mankind are revealed

Representation of movement patterns Sahelanthropus. Walking on two legs was common among the first known representatives of humanity, perhaps on the ground but also in trees. It coexisted with other types of locomotion in an arboreal environment, including quadrupedal locomotion using a firm fist, distinctly different from that of gorillas and chimpanzees who use the back of their phalanges for support (“knuckle walking”). Credit: Sabine Rivout, Guillaume Daffer, Frank Jay/Palevoprim/CNRS – University of Poitiers

A new study reveals that Sahelanthropus tchadensisthe oldest representative species of humanity, was bipedal.

It is believed that the evolution of walking on two legs was a turning point in human evolution. However, there is disagreement about its modalities and age, particularly due to the lack of fossilized remains. Researchers from the University of Poitiers French National Center for Scientific Research (CNRS)and its Chadian partners analyzed three bones in the extremities of Sahelanthropus tchadensis, the first known representative of the human race. The study was recently published in the journal temper naturesupports the hypothesis that walking on two legs was developed very early in human history, at a time still associated with the ability to move on four limbs in trees.

Frank Jay and Guillaume Davier

Group working session between Frank Jay (left) and Guillaume Duffer (right), at the PALEVOPRIM Laboratory, Poitiers (CNRS/University of Poitiers). Credit: Frank Jay/Palivoprim/CNRS – University of Poitiers

Sahelanthropus tchadensis It is considered the oldest representative species of humans, dating back 7 million years. Its description dates back to 2001 when the French-Chadian Expedition of Paleobiology (MPFT) uncovered the bones of three people in the Minala Toros in the Djarab Desert (Chad), including a well-preserved skull. This cranium, and in particular the direction and anterior location of the occipital foramen where the vertebral column is inserted, revealed some form of bipedal locomotion, meaning that she was able to walk on two legs.

In addition to the cranium, nicknamed Toumaï, and the fragments of the jaws and teeth already deployed, the Toros-Menalla 266 (TM 266) site yielded two ulna (forearm) and femur (femur). These bones are also attributed to Sahelanthropus Because no other large primates were found at the site; However, it is impossible to know if they belong to the same person as the skull. Paleontologists from the University of Poitiers, the National Center for Scientific Research, the University of N’Djamena and the National Center for Development Research (CNRD, Chad) recently published their full analysis in temper nature.

3D Models Sahelanthropus Tchadensis

Left: 3D models of the post-skull Sahelanthropus tchadensis. From left to right: femur in posterior and middle view; Right and left ulna, in front and side view. Right: an example of the analysis performed to explain the kinematic position of Sahelanthropus tchadensis. 3D cortical thickness contrast map of the femur (left to right) Sahelanthropus, an extant human, a chimpanzee, and a gorilla (in rear view). This analysis enables us to understand the differences in mechanical constraints on the femur and to interpret these constraints in terms of locomotor mode. Credit: Frank Jay/Palivoprim/CNRS – University of Poitiers

The femur and ulna were subjected to a range of measurements and analyses, regarding their external morphology and internal structures using microscopy: biometrics, geometric morphometrics, biomechanical indicators, etc. These data were compared with that of a relatively large sample of extant and fossilized apes: chimpanzees, gorillas, orangutans, Miocene apes, and members of the hominid group (OrorinAnd the Ardipithecusaustralopithecines, ancient to turn downAnd the A wise man).

The structure of the femur indicates this Sahelanthropus It usually walks on two feet on the ground, but perhaps also in trees. According to the findings of the ulna, this bipedal walking coexists in arboreal environments with a form of tetralogy, tree climbing enabled by a strong fist, distinctly different from those of gorillas and chimpanzees leaning on the back of their phalanxes.

Jarab desert

The Djarab Desert, where the fossil sites that yielded the post-cranial remains Sahelanthropus tchadensis Located. Credit: MPFT, PALEVOPRIM/CNRS – University of Poitiers

The conclusions of this study, including identification of the habit of walking on two legs, are based on the observation and comparison of more than twenty characteristics of the femur and ulna. It is, by far, the most miserly explanation for the combination of these traits. All of this data reinforces the concept of bipedal locomotion very early in human history, even if at this point other modes of locomotion were also practiced.

This work was supported by the French Ministry for Europe and Foreign Affairs, the Chadian government, the French National Research Agency (ANR), the Nouvelle Region of Aquitaine, the National Center for Scientific Research, the University of Poitiers and the French representation in Chad. It is dedicated to the memory of the late Yves Coppins, who pioneered and inspired MPFT’s work in the Jurab Desert.

Reference: “Postcranial Evidence for Bipedal Walking from the Late Miocene in Chad” by G.Daver, F. Guy, H.T. Mackaye, A. Likius, J.-R. Boisserie, A. Moussa, L. Pallas, P. Vignaud, and N. D. Clarisse, 24 August 2022, temper nature.
DOI: 10.1038 / s41586-022-04901-z

The study was funded by Région Nouvelle-Aquitaine, the University of Poitiers, and the National Center for Scientific Research.