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

Bipedalism, baby A. afarensis didn’t roam alone. by Jennifer Walter Updated: Feb. 20, 2024 Originally Published: Dec. 8, 2021 Tim Boyle/Getty Images News/Getty Images

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

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

Shutterstock 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.

Tim Boyle/Getty Images News/Getty Images

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 . Shutterstock

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? altmodern/E+/Getty Images

Carlos Carreno/Moment/Getty Images In the study, the researchers examined several theories for what made the prints including an ancient primate, early human, or even a bear.

Marcia Straub/Moment/Getty Images 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.

Chris Hellier/Corbis Documentary/Getty Images 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

NurPhoto/NurPhoto/Getty Images 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.

Peter Finch/Stone/Getty Images “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.

Richinpit/E+/Getty Images 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.

Ashley Cooper/Corbis/Getty Images

Arterra/Universal Images Group/Getty Images 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.

Viplove Jain / EyeEm/EyeEm/Getty Images 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.

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

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.

The footprints appear somewhat like chimpanzee and human prints.

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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