- BBC News World
A new study shows that the oldest known human ancestors actually walked on two legs.
The conclusions are based on the analysis of fossil bones found in Chad more than 20 years ago, which have only been analyzed now.
According to researchers, the remains belong to human ancestors who called them Sahelanthropus tchadensiswho lived between six and seven million years ago.
It would be the oldest known member of the hominin lineage, the evolutionary branch that passed from the common ancestor of humans and chimpanzees to modern humans.
When one of the main bones, the skull, was found analyzed in 2002, scientists named its owner a name. Tomai, meaning “life hope” in Chadic.
the new study Now published in Nature, it is based on an analysis of other bones, including the femur.
Whether Sahelanthropus tchadensis was bipedal has been debated for years. But the authors of the new work, from institutions in France and Chad, say they finally have an answer.
When were the fossils found?
The bones were discovered by researchers from France and Chad during an expedition in the Djurab Desert, north of the African country, in July 2001.
when he was first study On the skull, scientists led by paleoanthropologist Michel Brunet, of the University of Poitiers in France, noted that despite the small size of his brain, similar to that of a chimpanzee, Thomas had other characteristics of later humans, such as teeth and a face.
They also noticed that The direction of the hole at the base of Tomai’s skull seemed to indicate that he walked upright.
On the same 2001 expedition, researchers collected hundreds of other fossils.
The new study is based on the remains of the limbs, includingThe left thigh bone (femur) and two of the right and left ulna (the ulna, or ulna, is one of the bones of the forearm with a radius; it forms the elbow)”, the authors of the work point out in a popular article on The Conversation.
The femur was first analyzed in 2004 by student Aude Bergeret-Medina from the University of Poitiers.
Then Roberto Macchiarelli, the paleoanthropologist and student supervisor, agreed that the bone probably belonged to S. tchadensis. Despite this, it has not been proven that the femur, ulna, and skull belong to the same person.
Why did scientists take so long to analyze other remains found in Chad?
The study of the parties did not gain momentum until 2017.
“This was not one of our priorities,” said Frank Jay, a paleoanthropologist at Poitiers who led the latest research. temper nature.
In their article in The Conversation, the authors of the new study note that analysis of the material “has slowed considerably for a variety of reasons, including priority given to field investigation of other postcranial remains and other work, as well as a difficulty in analyzing such fragmentary material that requires additional insights.” It was relaunched in 2017, and it took five years to complete.”
What is the evidence that Tomei walked upright?
The oldest bipedal hominid fossil described so far was Orrorin tugenensis, which was found in Kenya and is six million years old.
However, the authors of the new study point out that the features of the femur and ulna found in Chad show that their owner has the ability to walk straight.
Scientists have compared these bones to a wide variety of primates and other human ancestors.
The authors note that, “Because the preservation of these long bones is not very good (femurs lost both ends for example), the brief analysis does not provide reliable explanations.”
“For this reason, we study them from all angles, both in their external form and in their internal structures.”
The researchers say they used more than 20 criteria to compare the remains with other bones from current and fossil specimens.
“If taken separately, none of these criteria can be used to suggest a conclusive interpretation of the substance.”
However, they add, Generally, he isCharacters have been found indicating that The “The Sahel region used to practice the usual walking on two legsmind _ mind“.
The authors relied on femur features that they observed are closer to those of humans than great apes.
Spanish scientist Pablo Pelaez-Campomanes is a researcher at the Museum of Natural Sciences in Madrid and was one of the authors of the study on Tomei’s skull in 2002.
“It represents the part of the femur that they have a series of morphological features such as the section of the bone, the thickness of the cortical layer of the bone and the shape of the various muscular additions, when compared with those of other species with different locomotion, that makes the most. It is likely and stingy to interpret this species as bipedal.” , the world explained to BBC Mundo.
“With regard to the ulna, it does not present characteristics of walking on two legs. The article concludes, also based on various morphological features (curvature, insertion, etc.), that it probably belonged to a species with arms adapted to a life with an important arboreal component.”
“Therefore, the combination of the ossicles with previous studies of the skull suggests that it was a bipedal species that retained bony adaptations related to arboreal behaviors.”
After that, Sahelanthropus could walk on its two legs when on the ground and easily climb trees.
Frank Jay stated that “when on the ground they preferred to move on two legs. But sometimes they chose to climb. All characteristics indicate this type of behaviour.”
Pelaez-Campomanis noted that the Sahelanthropus, according to the study, would have formed part of the so-called hominins, a subfamily of hominins.
The Spanish scientist explained: “In simple terms and according to the interpretations of this article, Sahelanthropus will be the first representative of hominins, which includes the clade that includes the genus Homo.”
“One of the characteristics that members of this species of hominin must have is the acquisition of walking on two legs, and therefore it is important that this species possess it so that it can be considered a hominin.”
Why does the study raise controversy?
In an article published in Nature accompanying the new study, Harvard paleoanthropologist Daniel Lieberman, who was not involved in the research, noted that the costal femur “looks more like a hominin bone than a four-legged ape.”
However, the debate continues.
Already in 2020, Aude Bergeret-Medina and Roberto Macchiarelli published a work based on measurements and photos, in which they argued that the owner of the famous femur did not walk upright.
Macchiarelli is not convinced by the new study, according to an article in the journal Nature.
The researcher asserts that the femur features described as indicative of walking on two legs could be the result of stress from being under sediments for millions of years.
Fred Spohr of the Natural History Museum in London told New Scientist that the authors of the new study “Good condition” for walking on two legsbut the debate is likely to continue.
Kelsey Pugh, of the Natural History Museum in New York, told the same publication that “it will be necessary for independent teams of paleoanthropologists to study these remarkable fossils in the coming months.”
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