Little Foot, one of the most complete hominid fossils in the world, may be a new species of human ancestor, according to a study that raises questions about our evolutionary past.
Little Foot, publicly unveiled in 2017, is the most comprehensive Australopithecus skeleton ever found. The foot bones that give the fossil its name were first discovered in South Africa 1994, leading to a painstaking 20-year excavation of the Sterkfontein cave system.
Professor Ronald Clarke, a paleoanthropologist from the University of the Witwatersrand who led the team that excavated the skeleton, attributed to Little Foot to mind Australopithecus Prometheus. Others thought it was Australopithecus africanusa species first described in 1925 and previously discovered in the same cave system.
Australopithecus – meaning “southern ape” was a group of hominins that existed in Africa as early as 4.2 million years ago.
But a new study by Australian researchers published in the journal American Journal of Biological Anthropologyfound that Little Foot's traits differed from both species, raising a third possibility.
“We think this is a previously unknown, unstudied species of human ancestor,” said Dr Jesse Martin, an associate professor at La Trobe University in Melbourne who led the study.
“It doesn't look like Australopithecus Prometheus … but it's also not like everyone else African leave Sterkfontein.”
Martin, also a research fellow at the University of Cambridge, added: “This thing will be part of the hominin lineage, so it's possible that we don't just have a point in our human family tree that we haven't discovered before, but a whole branch of that tree.”
Martin said that Clarke was “one of the few who argued that there were two species of hominins at Sterkfontein” and that he was “proven right” in this regard.
“Where [Clarke] and I'm leaving. I'd say definitely not Prometheus“, he said.
Researchers have identified key differences that differentiate Little Foot from Australopithecus africanusincluding the longer occipital plane, the area at the back of the skull.
“The lower part of the skull is supposed to be fairly conserved during human evolution, meaning it doesn't change as quickly,” Martin said. “If you find differences between objects at the base of the skull… those differences are likely to be across species because they just don't change easily, evolutionarily speaking. All the differences we found are in that area.”
“To find evidence of an entirely new species hiding in plain sight at Sterkfontein is kind of remarkable and counter-intuitive,” Martin added, given that “this is the most complete fossil of human ancestors in history.”
“We should be able to figure out where he fits in the human family tree.”
The study authors did not formally reclassify Little Foot, suggesting: “It is more appropriate that the new species be named by the research team that has spent more than two decades excavating and analyzing the remarkable Little Foot specimen. We hope that they will regard our proposal in this regard as well-intentioned advice.”
There is also disagreement among scientists regarding the age of Little Foot. The fossil skeleton has been dated 3.67 million yearsbut other scientists have suggested that Little Foot cannot be older 2.8 Ma.
Professor Ronald Clarke, who discovered the skeleton, has been contacted for comment.
