Little Foot fossil shows that the early human ancestor now clings to trees

A long-awaited, high-tech analysis of the torso of the famous fossil ‘Little Foot’ opens a window to an important period when human ancestors deviated from apes, according to new USC research.

Little Foot’s shoulder composition was the key to interpreting an early branch of the human evolutionary tree. Scientists at the Keck School of Medicine at USC have focused on the so-called chest strap, which includes collarbone, shoulder blades and joints.

Although other parts of Little Foot, especially its legs, display human characteristics for upright walking, the shoulder components are clearly ape-like, and the arms are surprisingly suitable for hanging from branches or up and down trees rather than around a projectile to throw or to hang the torso. like people.

The Little Foot fossil provides the best evidence yet of how human ancestors used their arms more than 3 million years ago, said Kristian J. Carlson, lead author of the study and associate professor of clinical integrative anatomical sciences at the Keck School of Medicine. .

“Little Foot is the Rosetta Stone for early human ancestors,” he said. “If we compare the shoulder composition with living humans and monkeys, it shows that Little Foot’s shoulder was probably a good model of the shoulder of the common ancestor of humans and other African apes such as chimpanzees and gorillas.”

The apical properties are likely to attract a lot of intrigue, as science teams around the world have been researching different parts of the skeleton to find clues as to the origin of humans. The USC-led study, which also includes researchers at the University of Wisconsin, the University of Liverpool and the University of the Witwatersrand in South Africa, is today in the Journal of Human Evolution.

The journal devoted a special issue to Little Foot analyzes from a global research group that looked at other parts of the animal’s skeleton. The process is somewhat related to the story of blind men and the elephant, each examining one part in collaboration with another to explain the whole of something not fully understood.

The Little Foot fossil is a rare specimen because it is an almost complete skeleton of an Australopithecus individual that is much older than most other human ancestors. The creature, probably an old female, stood about 4 feet long with long legs suitable for bipedal movement when it lived about 3.67 million years ago. Called ‘little foot’ because the first bones that were repaired consisted of a few small foot bones. The remains were discovered in a cave in South Africa in the nineties. Researchers have spent years digging it out of its rock shell and subjecting it to high-tech analysis.

Although not as widely known as the Lucy skeleton, another Australopithecus person was excavated in East Africa in the 1970s, but Carlson said Little Foot is older and more complete.

The USC-led research team has shrugged its shoulders because Little Foot is the oldest and intact example of this anatomy ever found. These legs give directions on how an animal moves. According to human evolution, these parts had to change shape before our ancestors could live free of trees, walk the open savannah, and use their arms for functions other than supporting the weight of the individual.

The scientists compared the creature’s shoulder parts with monkeys, hominins and humans. Little Foot was a creature adapted to live in trees because the chest belt represented a creature that climbed trees, hung under branches and used its hands above to carry its weight.

The shoulder blade, or shoulder blade, for example, has a large high ridge to attach heavy muscles similar to gorillas and chimpanzees. The shoulder joint, where the humerus connects, sits obliquely and is helpful in stabilizing the body and reducing the tensile load on shoulder ligaments when a monkey is hanging under branches. The shoulder also has a solid, apical reinforcing structure, the ventral beam. And the clavicle has a characteristic S-shaped curve that is common in monkeys.

The conclusions mean that the structural similarities in the shoulder between humans and African apes are much more recent and that they last much longer than suggested, Carlson said.

“We see indisputable evidence in Little Foot that the arm of our ancestors was still used 3.67 million years ago to carry significant weight during tree-like movements in trees to climb or hang under branches,” he said. “Based on comparisons with living humans and apes, we suggest that the shoulder morphology and function of Little Foot is a good model for that of the common ancestor of humans and chimpanzees from 7 to 8 million years ago.”

The scientists were able to obtain remarkably clear images of the fossils. This is because the bones, which have been carefully excavated for years, are in good condition and uniquely finished. The scientists examined them using micro-CT scans, which can detect small features on the surface of an object, peer deep into a bone, measure the density of an object and create a 3D model. generate without harming the fossil.