Another reconstruction of Lucy the Australophitecus, Natural History Museum, Washington DC Mpinedag

‘Lucy’ Walked Upright but Baby Australopithecines Lurked in Trees

Nearly-complete fossil foot found in Ethiopia shows young Australopithecus afarensis retained ape-like ability to grip branches

A rare fossil foot of a toddler Australopithecus indicates that while the adults walked upright on two legs and apparently lived on the ground, their kids may have clung to the trees for protection, says a paper published Wednesday in Science Advances, by Jeremy DeSilva of Dartmouth College and colleagues.

This was deduced from primitive, chimp-like characteristics of the baby’s foot, which would have been lost by adulthood if the child had survived. Which it didn’t.

Fossils of hominins are extraordinarily rare. Only 10 fossils of australopithecine afarensis have been discovered so far, none complete, says Prof. Yoel Rak of Tel Aviv University, an expert on the subject. The first was “Lucy,” the partial skeleton of a female found in Ethiopia, which was dated to 3.2 million years ago.

The remains are of a toddler around 2 to 3 years old, still with a full mouth of milk teeth. Found in Dikika, Ethiopia in 2002, the skeleton of young Selam – as the juvenile has been dubbed – has been dated to 3.3 million years.

Selam has been categorically identified as belonging to the same species as Lucy, despite being around 100,000 years older.

Sure, the australopithecines could have developed a lot during that 100,000 year difference, but there is no question that Selam is the same species because the archaeologists found critical mass of his remains, explains Rak, who has studied Lucy extensively. Extraordinarily, they didn’t find isolated bones scattered about; they found almost the whole skeleton in a single body of rock – skull, vertebrae, feet and all.

Lucy’s feet were not found, Rak clarifies. But the feet of other adult australopithecines were discovered, enabling the comparison with the juvenile.

Adult Australopithecus afarensis feet were very human-like. The baby’s feet were a little more ape-like. It could grasp branches with its feet.

Baby had chimp-ish feet

Archaeologists today concur that Lucy and her brethren were bipedal like us, a conclusion based on multiple avenues of evidence.

One is fossil footprints preserved in volcanic ash found in Laetoli, Tanzania, and dated to about 3.6 million years ago.

The 27-meter (88-foot) trail of prints is believed to have been made by early Australopithecus afarensis on the grounds that its remains were found in the same sediment layer, and no other hominins are known to have existed at that time. These proto-people were definitely walking upright.

A second avenue of evidence is the fossil feet of adult australopithecines. The adults’ feet were like ours and unlike those of our cousin the chimpanzee in two chief ways, explains Rak (who was not involved in this research).

One very human characteristic that Lucy shared was a massive heel. Knuckle-walking apes don’t have that.

Humans need robust heels because our step begins with our heel striking the ground, Rak explains: that load needs to be dissipated. Apes have relatively gracile heel bones.

Having struck the ground with our heel, we then propel ourselves forward using our big toe, which is in line with the sole and also grouped with our other toes.

“Our big toe does not deviate medially from the sole,” Rak says. “This is crucial because that’s what enables us to propel the body and progress forward with each step.”

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