It has been for a while since scientists were aware that the early ape-like hominid A. afarensis was part of our family tree, and walked on two feet.
A almost complete foot from Dikika, Ethiopia and its implications for the ontogeny and function of Australopithecus afarensis.
"For the first time, we have an awesome window into what walking was like for a (2.5)-year-old, more than 3 million years ago", Jeremy DeSilva, an associate professor of anthropology at Dartmouth College, in Hanover, N.H. and lead author in the study, said in a statement.
"Studying younger individuals is important because the morphology that you see in adults is the result of both their evolution through time and how they changed as they grew", Alemseged, senior author of the study, wrote in an email.
An ancient 3-year-old was a tree climber, experts have deduced after studying her fossils dating back to more than 3 million years ago.
This is the 3.32 million-year-old Australopithecus afarensis foot from Dikika, Ethiopia, superimposed over a footprint from a human toddler.
However, juvenile specimens of most human hominin ancestors are scarce, and thus, it has been hard to trace how important traits are selected in animals, over time.
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.
According to CNN, Selam was similar in size to a chimpanzee and depended on her mother for survival.
The group took a close look at the rare toddler skeleton, named Selam, and noted signs of ape-like features on its foot.
They examined what the extremity would have been used for, how it developed, and what it tells us about human evolution (spoiler: our progenitors were "quite good" at walking upright).
"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. What's more, the toddler found in Dikika, Ethiopia, was probably better at climbing than her parents. 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. But fossilized hints-namely the base of the big toe-hint that children spent more time in trees than adults.
Although skeletons like Selam and Lucy are incredibly important for anthropologists, they also show just how little scientists know about our ancestors.
Alemseged believes that all of this evidence combined shows what a critical, pivotal species afarensis was for human evolution. The new study supports many previous studies that the foot in A. afarensis was adapted for upright walking and was largely human-like.