Study shows ancient ancestors climbed trees, also walked on two legs

James Marshall
July 8, 2018

Lead author Jeremy DeSilva is an associate professor of anthropology and a world authority on the feet of our earliest ancestors.

Only three years old when she died, Selam was already bipedal. In 2002, archaeologists discovered a well-preserved, partial skeleton of an infant A. afarensis, thought to be around 3-years-old at the time of death. In the capacity of a small foot of an ancient female, it is merely the size of a human thumb and forms a part of an originally larger whole.

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.

The fossil of the toddler's foot was the most intact piece of bone that has ever been unearthed from our distant past.

"For the first time, we have an wonderful window into what walking was like for a 2½-year-old, more than 3 million years ago", Jeremy DeSilva, lead study author and an associate professor of anthropology at Dartmouth College, said in a statement. Alemseged is internationally known as a leading paleontologist on the study of human origins and human evolution. He contributed to the study as a senior author.

Australopithecus afarensis was similar to chimpanzees, growing rapidly after birth and reaching adulthood much earlier than modern humans, The Smithsonian National Museum of Natural History noted. "The Dikika foot adds to the wealth of knowledge on the mosaic nature of hominin skeletal evolution" explains Alemseged.

The fossil record shows that these ancient ancestors were adept at walking upright. At 2½ years old, Selam would've been walking on two legs. "But, walking poorly in a landscape full of predators is a recipe for extinction", DeSilva said in the statement.

The fossil is the same species as the famous Lucy fossil and was found in the same vicinity in Dikika in Ethiopia. Later, Selam was found just a few miles away from Lucy and was then given the nickname "baby Lucy", despite being alive around 200,000 years before Lucy.

Remarkably well preserved, the foot allows researchers to reconstruct a picture of life-specifically for toddlers-millennia ago. After an examination into how the foot developed and what this tells us about human evolution, it can even start to tell the story of how our ancestors survived. It was a female child of nearly two-and-a-half years old. This attribute could have allowed them to cling to their mothers, climb trees and outsmart predators.

"Every fossil gives us some bit of our past, [but] when you have a child skeleton, you can ask questions about growth and development-and what the life of a kid was like three million years ago", DeSilva told National Geographic. So although the afarensis toddlers could walk, they probably spent more time in trees than on foot, unlike adults.

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