Bipedalism, baby

Look: 3.6-million-year-old prints likely belong to an undiscovered ancient human

A. afarensis didn’t roam alone.

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In the late 1970s, paleoanthropologists digging in modern-day Tanzania discovered something remarkable.

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They unearthed a series of fossilized footprints made 3.6 million years ago and preserved in volcanic ash.

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At the time, they weren’t sure who the footprints belonged to.

Were they made by animals, or perhaps an early human ancestor?

Some of the tracks were later identified as footprints of Australopithecus afarensis, a hominin species that lived in Eastern Africa between 3.85 and 2.95 million years ago.

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But there was another set of prints — and it has perplexed researchers for decades.

The prints appear to have been left by an individual walking on two legs with wide, small feet, and a strange, cross-stepping gait.

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McNutt et. al, Nature

A team of researchers recently went back to the site to investigate further — discovering the prints may be a sign of a totally unknown hominin species.

The ancient hominin that left these tracks is a mystery, but they can help answer a fundamental enigma in the human story.

Specifically: When did hominins — and humans — first walk upright?

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In the study, the researchers examined several theories for what made the prints including an ancient primate, early human, or even a bear.

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They watched black bears for more than 50 hours — they walk upright sometimes, but it doesn’t seem habitual enough to suggest bears are the culprit.

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And finding fossils of bear relatives that fall in the genus Ursus is extremely rare in Eastern Africa, so the researchers ruled that hypothesis out.

The footprints appear somewhat like chimpanzee and human prints.

McNutt et. al./Nature

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In a Nature column, paleoanthropologist Stephanie M. Melillo notes the footprints have a mix of human and chimp-like features we don’t see in any living creature today.

“The footprints themselves are oddly wide and short, and the feet responsible for their creation might have had a big toe that was capable of thumb-like grasping, similar to the big toe of apes.

Paleoanthropologist Melillo, writing in Nature.

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Melillo also writes that scientists don’t typically define new species based off footprints alone.

In order to determine if the tracks represent a new type of hominin, researchers would need to identify other remains, such as skulls, jawbones, or teeth.

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The simplest explanation, the researchers argue, is that we have another ancestor we don’t know about — and an exciting future discovery for paleoanthropologists to make.

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If that’s the case, this archaic hominin would have likely coexisted with A. Afarensis — offering new insight into intra-species cooperation between our ancestors.