One of the Most Complete Human Ancestors Ever Found Isn’t Who We Thought It Was

In 1998, researchers discovered one of the most complete known human ancestral fossils in South Africa’s Sterkfontein Caves. Almost two decades later, Ronald Clarke, the paleoanthropologist who had led the excavation and analysis, identified the remains as an Australopithecus prometheus, while others argued it was an Australopithecus africanus. New research suggests it’s neither.

In research published last month in the American Journal of Biological Anthropology, researchers have challenged the classification of StW 573, nicknamed “Little Foot,” pointing to the possibility of a previously undocumented human species.

A new human relative?

“This fossil remains one of the most important discoveries in the hominin record and its true identity is key to understanding our evolutionary past,” Jesse Martin, lead author and University of Cambridge postdoctoral research fellow, said in a La Trobe University statement. “We think it’s demonstrably not the case that it’s A. prometheus or A. africanus. This is more likely a previously unidentified, human relative.”

Australopithecus is an extinct group of ape-like modern human relatives—or potentially ancestors—that walked upright and existed in South Africa between 3 and 1.95 million years ago. Martin and his colleagues concluded that Little Foot and A. prometheus, as well as Little Foot and A. africanus, do not have a unique set of characteristics in common. They are the first to question the remains’ identification since they were revealed to the world in 2017.

“Our findings challenge the current classification of Little Foot and highlight the need for further careful, evidence-based taxonomy in human evolution,” explained Martin, who is also an adjunct at La Trobe University. Moving forward, Martin and La Trobe University students will investigate Little Foot’s species and its position in the human family tree.

Insight into early humans

According to La Trobe paleoanthropologist Andy Herries, the remains are among the most complete and important fossils ever found, offering key insights into early human diversity and how our ancestors adapted to the different environments of southern Africa. At La Trobe, Herries directed an Australian Research Council grant that supported the new research.

“It is clearly different from the type specimen of Australopithecus prometheus, which was a name defined on the idea these early humans made fire, which we now know they didn’t,” Herries explained. “Its importance and difference to other contemporary fossils clearly show the need for defining it as its own unique species.”

It remains to be seen what Martin and the students’ investigation will conclude about Little Foot—the most complete known ancient hominin fossil—and how the rest of the scholarly community will take it.