Little Foot kicks more great big evolutionary clues our way
New evidence tells us more about our ancestors’ transition from tree-dwelling apes to walking upright
While most of us are preoccupied with a birth in the Middle East 2,000 years ago, scientists are counting their blessings for a death in South Africa 3.67 million years earlier.
Little Foot, a skeleton from the Sterkfontein caves, is yielding an avalanche of clues to the ancestry of modern man, and two of them have just emerged.
The first shows that our ancestors learned to walk upright even when they were still primarily living in trees, while the second provides insight into the early hominin brain and its large visual cortex, which is more similar to chimpanzees than to humans.
Little Foot, found in 1994, is unusually complete and well-preserved, allowing scientists to make accurate measurements of its bones.
Their findings have now changed our understanding of the evolutionary move from climbing in trees with longer arms than legs to being bipeds with longer legs than arms and walking upright.
The new finding is by an international team that includes Professor Ronald Clarke from Wits University, who discovered Little Foot. The research is on the brink of being published, but awaiting peer review.
Professor Robin Crompton, lead author from the University of Liverpool, said: “This hominin, for the first time in the fossil record, had longer lower limbs than upper limbs, like ourselves.
“That means she was being selected for long stride length in bipedalism. Moreover, Little Foot had a hip joint like our own, able to transmit large forces from the trunk to the leg and vice versa.”
Although her legs were longer than her arms, they had “not yet achieved the great relative leg length found in humans”.
“Thus, she would not have been as good at carrying objects as we are,” but she would have been much better at climbing trees than modern humans.
The finding about Little Foot’s brain is based on the first cast of the inside of her cranium – known as an endocast – which has allowed scientists to reconstruct the fossil’s nearly complete brain.
The endocast was virtually extracted, described and analysed by Wits University researcher Amélie Beaudet and the Sterkfontein team, based on MicroCT scans of the fossil.
It shows Little Foot’s brain was small and had some features similar to human brains, while others were closer to the ancestor humans share with chimpanzees.
The scans reveal impressions left on the skull by the brain and the vessels that feed it, as well as the shape of the brain.
Beaudet’s research has been released as the first in a series of papers planned for a special issue of the Journal of Human Evolution about Little Foot.
“Our ability to reconstruct features of early hominin brains has been limited by the very fragmentary nature of the fossil record. The Little Foot endocast is exceptionally well preserved and relatively complete, allowing us to explore our own origins better than ever before,” said Beaudet.
The endocast showed that Little Foot’s brain was asymmetrical, as are the brains of humans, living apes and younger hominin endocasts. Little Foot’s early asymmetry supports suggestions that the feature was probably present in the last common ancestor of hominins and other great apes.
Other brain structures, such as an expanded visual cortex, suggest the brain of Little Foot probably had some features that are closer to the ancestor we share with chimpanzees.
“In human evolution, we know that a reduced visual cortex, as we can see in our own brain, is related to a more expanded parietal cortex – which is a critical cerebral area responsible for several aspects of sensory processing and sensorimotor integration,” said Beaudet.
The study also showed that the vascular system in Australopithecus was more complex than previously thought.
“This would mean that even if Little Foot’s brain was different from us, the vascular system that allows for blood flow and may control temperature in the brain – both essential aspects for evolving a large and complex brain – were possibly already present at that time,” said Beaudet.
Little Foot’s brain suggested younger hominins evolved greater complexity in certain brain structures over time, perhaps in response to increasing environmental pressures.
“Such environmental changes could also potentially have encouraged more complex social interaction, which is driven by structures in the brain,” said Beaudet.
The latest discoveries provide further proof of the incalculable value of Little Foot to palaeontologists: it was a single moment in time millions of years ago when she was on the run, possibly from a predator, and made a misstep that saw her plunge down a 20m shaft and die.
Her mishap gave scientists millions of years later the gift of a skeleton preserved by layer upon layer of natural material that shifted around and encased her.
LITTLE FOOT, GIANT LEAP
The modern-day story of Little Foot began in 1994 when Professor Ronald Clarke from Wits University discovered four bones from a left foot lying in a box of animal bones from the Sterkfontein cave system.
Three years later, in another box, he found more bones from the same foot and set out to find the skeleton they came from.
He and his assistants located a single bone sticking out of a rock, and it took a further two decades to extract the Little Foot skeleton from her rocky matrix and then clean, restore and analyse the bones.
The bone is very delicate and in some cases paper thin, which makes analysis a painstaking process. But it has paid off.
Little Foot was officially unveiled last year when Clarke and his team had removed enough bones to reconstruct more than 90% of the skeleton.
According to science journal Nature, “no other Australopithecus fossil comes close to that level of completeness”.
Lucy, the most famous Australopithecus found in Ethiopia, is by comparison only 40% complete.
Little Foot’s birthday was only confirmed in 2015 when scientists finally concluded, after furious debate, that she was 3.67 million years old.
The dating changed our understanding of our ancestry because Lucy was previously pegged as being much older than Little Foot.
But when it was confirmed that they were contemporaries, it told us there could well have been many species of Australopithecus (an upright walking hominid with human-like teeth and hands) extending over a much wider area of Africa.