There is evidence that this human-like species walks upright.
An artistic interpretation of how the Sahel people moved.
A new study has found that the oldest known humanoid species may have walked on two legs 7 million years ago, revealing the initial difference between humans and great apes.
According to the Smithsonian National Museum of Natural History, the researchers analyzed a thigh bone (femur) and a pair of forearm bones (ulna bones) of the Chadian Shahe, who may be the oldest known ancient human being — a relative of humans dating back to the split of our ancestors from modern apes. First excavated in 2001 in Chad in northern Central Africa, the remains are about 7 million years old.
Examination of its femur and ulna suggests that the Chadian Shakh not only walked on two feet, but also climbed trees, further proving that this mysterious species was bipedal, as early analysis of its skull dissection suggested.
3D models of these arm and leg bones. From left to right: femur; Left and right ulna.
Many features distinguish humans from existing close relatives chimpanzees and bonobos, such as our brains, upright postures, parachonnas, and largely hairless bodies. However, it is uncertain which of these traits began to separate chimpanzee and bonobo lineages from paleoanthropteran lineages, which previous studies believe occurred between 6 million and 10 million years ago.
The part of the skull of the Chadian Shah found by scientists reveals that the species may be close to chimpanzees in size and structure. The researchers say that while its brain also looks chimpanzee-sized, its face and teeth are closer to those of ancient humans, suggesting it may be a close relative of the last common ancestor of humans and chimpanzees.
Judging by the large and protruding brow ridge on the skull, the specimen, nicknamed "Toumaï" by the researchers, may have been male. (In the local Golan language, "Toumaï" means "the hope of life.") The name is usually given to babies born near the dry season, in the vast, flat, windy Durab Desert in northern Chad, where fossils were unearthed. )
Chad's Djurab Desert, where researchers have excavated fossil remains of Chadian Shah humans.
Perhaps the most interesting feature that Toumaï shared with other ancient humans is the opening at the base of the skull, where the spinal cord appears. For tetrapods, this opening is usually located at the back of the skull and is backwards. However, in the Chadian Shah, this opening is located near the middle of the skull and is downward. This suggests that the Chadian Shah is a biped, meaning it walks on two legs.
Toumaï supports the idea that bipedal walking may have helped distinguish the earliest ancient humans from their relatives. So far, however, in addition to this skull, researchers have only learned about chadian shakhs (Chadian apes) from some jawbone fragments and some teeth. Because there are no more bones in other parts of the body, some researchers have reserved judgments about whether chadian apes are bipedal.
Ancient leg bones and arm bones
Franck Guy (left) and Guillaume Daver (right) at the Palevoprim lab in Poitiers, France
In the new study, the researchers analyzed three other fossils associated with Chadian apes — the femur and two ulna bones. Scientists first discovered these arm and leg bones at the same time and place as other Chadian ape fossils. The team believes the fossils are related to Chadian apes because no other macrobrains have been found in the area, though they say it is impossible to know whether the fossils belong to Toumaï.
The researchers analyzed the external shape and internal microstructure of the bones. Next, they compared the data with the corresponding details of extant and fossil species, including chimpanzees, gorillas, orangutans, great apes that became extinct at the same time, modern humans, ancient humans such as ground apes, and Australopithecus australopithecus (Australopithecus and its close relatives).
The base of the femur neck appears to be slightly towards the front of the body and flattened, and the upper part of the thigh bone is slightly flattened – all of these features have appeared in known bipedal archaeopterans. In addition, the parts where the hip muscles are attached are very strong, much like humans. The cross-sectional shape of the femur suggests that it can resist the lateral bending forces seen when walking on two legs.
All these findings on the femur suggest that Chadian apes are usually bipeds, either on the ground or in forest canopy.
We can see (from left to right) a map of the change in the thickness of the 3D cortical thickness of the chadian Shah, humans, chimpanzees and gorillas femurs.
Our study shows that Chadian species have a select set of anatomical features that clearly suggest that the oldest known representatives are bipedal walks on the ground and on trees.
In contrast, the bones of the left and right forearms resemble chimpanzees and are well adapted to climbing trees; They have highly curved shafts, which indicate the presence of strong forearm muscles, and the shape of the elbow joints indicates that they can cope with high-intensity forces when bent.
The femur does not preserve the joints at both ends, so it needs to be proved that the key features of bipedal walking are missing, but they do a good job with existing resources.
All in all, the key finding is that the earliest ancient humans were some sort of biped, which further proves that the evolution of bipeds is responsible for the divergence of the human lineage from apes. But, like our surviving chimpanzee relatives, early archaic humans still retained the ability to climb trees.