Researchers at the University of Southern California (USC) have analyzed the upper body of a 3.67 million-year-old fossil called Little Foot, and the published findings offer insight into the time when humans separated from apes, according to a study published in Journal of Human Evolution.
‘Rosetta Stone for Early Human Ancestors’
The long-awaited analysis is based on the scientific achievements of clear images of fossils. Little Foot is a rare, almost complete fossil skeleton of Australopithecus discovered in the Sterkfontein cave system in South Africa in 1994, and unlike the widely known Lucy, it is older and more complete. Probably an old female person, she stood about 4 meters long with long legs suitable for two-legged movement, according to a USC press release.
It got its name because the first bones recovered were a few small foot bones. The excavation of the concrete-like stone took years, and so did the high-tech analysis of its uniquely complete bones, which are in good condition.
“A small foot is a Rosetta stone for early human ancestors,” said Christian J. Carlson, lead author of the study and associate professor of clinical integrative anatomical sciences at Keck Medical School. “When we compare the shoulder assembly with living humans and monkeys, it shows that the Little Foot shoulder is probably a good shoulder model of the common ancestor of humans and other African monkeys like chimpanzees and gorillas.”
The bones were examined using technology that can detect tiny characteristics on the surface of the object, examine the inside of the bone and generate a 3D model without damaging the fossil called a micro-CT scan.
Determining the moment when humans and monkeys parted ways
The team of scientists focused their research on the shoulder area, especially on the collarbones, shoulder blades and joints, which gives indications of how the animal moves. At that time, the shoulder area was compared to monkeys, hominins and humans.
While the other limbs of the fossil, especially the legs, showed human traits that could allow him to walk upright, his shoulders were distinctly ape-like and showed that the Little Leg was adapted to life on trees. Carrying arms can allow him to hang from branches, use his arms above his head to lower himself to a load, or go up and down trees.
“In Little Foot, we see irrefutable evidence that the hand of our ancestors from 3.67 million years ago was still used to carry significant weight during tree-lined climbing or hanging under branches,” Carlson explained. “In fact, based on comparisons with living humans and apes, we suggest that shoulder morphology and the function of the Little Foot are a good model for the common ancestor of humans and chimpanzees 7 to 8 million years ago.”
This could mean that structural similarities in the shoulder area between humans and monkeys have occurred much more recently than previously suggested.