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Foot fossil of juvenile hominin exhibits ape-like features

08 July 2018

The study titled, "A almost complete foot from Dikika, Ethiopia and its implications for the ontogeny and function of Australopithecus afarensis", was published July 4 in the journal Science Advances.

"For the first time, we have an fantastic window into what walking was like for a two-and-a-half-year-old, more than 3 million years ago", said lead author Jeremy DeSilva, Associate Professor at Dartmouth College in New Hampshire.

The evidence comes from DIK-1-1 - a relatively complete 3.3 million-year-old skeleton of a 2.5- to 3-year-old female Australopithecus afarensisdiscovered in Dikika, Ethiopia. On the other hand, the researchers discovered that Australopithecus Afarensis primitive humans possessed 12 pairs of ribs and thoracic vertebrae precisely as many as the modern humans.

Although this 3.32-million-year-old fossil from Dikika, Ethiopia, was announced in a previous 2006 study, numerous skeleton's elements, including the partial foot known as DIK-1-1f, were encased in sediment and therefore had to be carefully uncovered. That the little female juvenile that existed 3 million years ago was spending time in the trees shows that she was partially in need of her mother's protection.

Unsurprisingly, this led to it being erroneously called "Lucy's baby" by the popular press - despite this toddler having been around 200,000 years before Lucy. But unlike the chimp's big toe, Selam's is in line with her other toes, similar to toes on a human foot. He unearthed Selam's foot back in 2002.

Without so many amenities in those primitive times, many early humans especially weak toddlers had to climb trees and stay put so that predators remained away from them.

Bridging the gap between humans and chimps, Lucy had slightly curved fingers and toes, with mobile ankles and shoulders that provided more overhead range of movement.

"If you were living in Africa 3 million years ago without fire, without structures, and without any means of defence, you'd better be able get up in a tree when the sun goes down", adds DeSilva. "We think that this helps explain the differences we see between the bones of the Dikika toddler and the more human-like bones of the adults".

The anatomy of Selam's foot was incredibly well-preserved, allowing the researchers to study how a toddler hominin would have walked.

Members of the species had both ape and human characteristics and could walk upright but also live in trees. They found the big toe was more capable of moving side-to-side than skeletons of similar adult feet, meaning it would be better at climbing through branches and latching onto its mother.

These findings could shed light on the evolution of walking upright and shows how crucial the afarensis species was for human evolution. However, the fossil record suggests ancient adults spent more time on the ground.

Foot fossil of juvenile hominin exhibits ape-like features