'Sahelanthropus', the ancestor of the first biped

Analysis of the remains of Sahelanthropus tchadensis, discovered in Chad in the 2000s, revealed that the species was walking on two legs 7 million years ago. Even so, experts debate whether it was actually a quadruped.

Analysis of the remains of Sahelanthropus tchadensis, a species discovered in Chad in the 2000s, confirms that it went bipedal more than 7 million years ago.Even so, experts continue to debate whether it was really a square.

Sahelanthropus Tchadensis is established as the oldest bipedal ancestor.As their bones, from 7 million years ago, have apostles, their role is similar to hominids, according to research reported in Science Advances.

This work is based on a combined analysis of the ulna and two parts of the femur.Sahelanthropus tchadensis, a species discovered in the Djurabi Desert (Chad) in the early 2000s, has been the subject of much debate over whether it is bipedal or not.

Sahelanthropus tchadensis was a bipedal ape that had a brain the size of a chimpanzee and probably spent most of its time in trees.

The first studies focused on the skull, and only twenty years later research began on the arms and femur to answer the question of whether we are dealing with a human ancestor.

"Shaheimanthus chadiensis was a bipedal great ape with a brain about the size of a chimpanzee that likely spent most of its time in trees foraging for food and shelter. Nevertheless, it adapted to bipedal posture and locomotion on the ground," said Scott Williams, an anthropologist at New York University and one of the authors of the study.

Williams and the rest of the team further examined the ulna and femur of Sahelanthus chidensis using two methods: multiple comparisons of the same bones from living and fossil species, and 3D geometric morphology, an advanced method that allows their shapes to be studied in great detail.

Among the fossil species they compared the remains to was Australopithecus, the human ancestor known for the discovery of the Lucy skeleton, a famous 4- to 2-million-year-old fossil found in Ethiopia in 1974.

According to the joint study, the authors identified three features that indicate that Sahelantropus was bipedal.On the one hand, the presence of a point of connection between the pelvis and the thigh, which has so far only been found in hominids and is necessary for upright walking.

On the other hand, the presence of a special hominid torsion that helps the legs move forward, thus making it easier to walk.And finally, the presence, deduced from the 3D analysis, of the gluteal muscles similar to those of the first hominids, which keep the hips stable and help the body to stand, walk and run.

Although these last two characteristics, hamstring torque and gluteal torque, have already been identified by other scientists, this study confirms their existence.

The authors also found that Anthropus had a long femur compared to the ulna, which is additional evidence for bipedalism.

Apes have long arms and short legs, while apes have relatively long legs.Although the legs of Sahelanthropus were much shorter than those of modern humans, they differed from ape legs and were closer to the femur length of Lucy, another adaptation for bipedal walking.

"We have compelling evidence that Sahelanthropus tchadensis can walk on two legs, that bipedalism evolved early in our lineage and from an ancestor very similar to modern chimpanzees and bonobos," New York University's Williams said in a statement.

"The relevance of this paper is that the manifestations of bipedalism in Sahelanthropus are so old that it would be close to the evolution of two lines leading to apes and humans," says researcher Joseph Maria Potau of the University of Barcelona.

“El desarrollo de un bipedismo en Sahelanthropus tchadensis, compartido con otros tipos de locomociones arbóreas habituales, apoyaría la posición de este primate fósil en la línea evolutiva de los humanos, situándose muy cerca del ancestro común del que partieron hace unos 7 millones de años las dos líneas evolutivas que dieron lugar a los chimpancés y a los humanos actuales”, añade Potau.

However, José-Miguel Carretero, director of the Laboratory of Human Evolution at the University of Burgos, believes that the study still does not resolve the debate about the origins of bipedalism because the remains found so far are not informative enough to fuel the debate.

"If the fossils themselves say one thing and the opposite, they must be clearly insufficient," he noted.

Williams, S.A., et al. The first evidence of hominin bipedalism in Sahelanthropus tchadensis.Advances in Science (2026).