Ancient human ancestor ‘Little Foot’ probably lived in trees, new research finds

Around 3.67 million years ago, an ancient human ancestor nicknamed Little Foot fell about 30 feet down into a deep shaft of a cave. Today, she represents the most complete Australopithecus (pronounced aa-struh-luh-pi-thuh-kuhs) skeleton and is helping researchers to learn more about our chimpanzee-like ancestors.

Little Foot likely stood over just four feet tall. She would have slept in trees to remain safe from giant predators like sabre-toothed cats. And she was likely a vegetarian who munched on plants. Little Foot had powerful hands and a special big toe that allowed for better climbing.

This week, researchers studying her skeleton learned something new. They shared that Little Foot was capable of different head movements than modern humans. This was likely due to the fact that Little Foot spent so much time in trees and was an expert climber. Humans have lost those special abilities and don’t need their heads to move as far back or forward.

That discovery is thanks to the fact that Little Foot retained her atlas, or the topmost cervical vertebrae between the head and neck.

In addition to understanding more about head movements, the atlas can also share information about blood flow to the brain through vertebral arteries.

The researchers discovered that the facets allowing for articulation between the head, first vertebra and second vertebra are more concave for Little Foot than modern humans, said Amélie Beaudet, study author and researcher at the University of the Witwatersrand in Johannesburg, South Africa.

This controls how the head moves up and down.

“These features might be useful for Australopithecus when climbing trees,” Beaudet said.

Little Foot’s atlas is similar to those in modern chimpanzees, as are her ligaments. Chimpanzees spend about eight or nine hours a day in trees and sleep in nests they’ve built there to remain safe from predators. Australopithecus likely did the same.

The researchers were also able to estimate blood flow to the brain, based on the skull and vertebrae. Little Foot’s blood flow to the brain, and likely the use of glucose by the brain, was three times lower than modern humans. This is also similar to chimpanzees.

“The low investment of energy into the brain of Australopithecus could be tentatively explained by a relatively small brain of the specimen, a low quality diet [low proportion of animal products] or high costs of other aspects of the biology of Australopithecus [such as upright walking],” Beaudet said. “In any case, this might suggest that the human brain’s vascular system emerged much later in our history.” The study published this week in the journal Scientific Reports.

Previously, Beaudet studied the endocast of Little Foot, or the imprint of the brain preserved on the inside of the skull, along with her inner ear structure. Little Foot’s inner ear provided insight not only about her hearing, but her sense of balance.

“I could demonstrate that the shape of the inner ear was compatible with activities in the trees and the ground, which is confirmed by our new study of the atlas,” Beaudet said. “Moreover, the reconstruction of the brain showed that it was three times smaller than ours and that the organization was very different from us, meaning that the emergence of a human-like brain occurred later in our history.”

Compared with younger Australopithecus skeletons, Little Foot spent more time in trees.

“A southern African Australopithecus specimen [later] than ‘Little Foot’ [probably younger by about 1 million years] may have partially lost this capacity and spent more time on the ground, like us today,” Beaudet said.

Who was Little Foot?

Australopithecus is thought to be our potential direct ancestor, the researchers said. Studying Little Foot provides researchers with an opportunity to look back at ancient ancestors who walked upright — long before the rise of the first humans.

These fossils have been found in South Africa over the years, leading to its naming as the “cradle of humankind.”

Little Foot got her name because she was first known based on the discovery of four foot bones found in 1995 by University of Witwatersrand researchers Ron Clarke and Philip Tobias. Tobias died in 2012.

From those four bones alone, they were able to determine that the creature combined both human and ape-like traits, Beaudet said. The bones also revealed Little Foot walked on two legs.

Most of her skeleton was found embedded in sediment of South Africa’s Sterkfonetin Cave, including a complete skull. It took Clarke and his colleagues 20 years to painstakingly unearth it.

“She may not be perfect in formed body, with some bones missing, but Little Foot is our great-great aunt many times removed and she is perfect to me,” Clarke famously said when Little Foot was revealed to the world in 2017.

Since then, Little Foot has been scanned and studied by researchers at the University of Witwatersrand, which remains her home. Beaudet began studying Little Foot in 2017.

Multiple Australopithecus species lived in Africa around three million years ago, including anamensis, africanus and afarensis like the famed Lucy skeleton. It’s possible that Little Foot belonged to the prometheus species, but it hasn’t been confirmed by the researchers yet.

” Australopithecus had a small brain, large teeth and males and females were really different from each other — while humans have a large brain, smaller teeth and human males and females are less distinct,” Beaudet said. “Australopithecus could climb trees and walk on the ground while we, humans, have lost the capacity of climbing and moving in trees like Australopithecus.”

More questions remain about Little Foot and the researchers will continue studying her unique fossil. Her crushed and deformed skull presents a challenge, so they are using scans to virtually separate and reassemble the bone fragments. This will better allow them to have a complete picture of what the Australopithecus skull looked like and compare it to others. Her hip bones will also need to be virtually reconstructed. And they can also learn more about her diet based on her teeth.