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

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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

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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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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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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