No larger than a human thumb, it belonged to a primate type called the hominid - who would have likely been our precedents - and it sheds some light on how our early ancestors could have been.
The fossil of the toddler's foot is not only the same species as the famous Lucy fossil, but was also found in the same vicinity in Ethiopia.
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.
The tiny foot, about the size of a human thumb, is part of a almost complete 3.32-million-year-old skeleton of a young female Australopithecus afarensis discovered in 2002 in the Dikika region of Ethiopia by Zeresenay (Zeray) Alemseged, a professor of organismal biology and anatomy at the University of Chicago and senior author of the study. ScienceDaily. ScienceDaily, 4 July 2018.
This is the 3.32 million-year-old Australopithecus afarensis foot from Dikika, Ethiopia, superimposed over a footprint from a human toddler. But unlike the chimp's big toe, Selam's is in line with her other toes, similar to toes on a human foot.
Although Lucy and Selam were found in the same area, Selam is not "Lucy's baby".
"So, it's human-like in not sticking out to the side, but it had much more mobility and could probably wiggle and grab on to stuff".
According to the lead author of the paper, Jeremy DeSilva from Dartmouth College, the features of Selam's foot seem to suggest that while being fully adapted to standing and walking on two feet, this infant A. afarensis could climb the trees easily.
The anatomy of Selam's heel was also surprising, he said.
"Walking on two legs is a hallmark of being human, but walking poorly in a landscape full of predators is a recipe for extinction", DeSilva said. "Even though we have the same anatomy they had, we got it differently".
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. That's an inference based on the fact there is no evidence of fire or construction for another million years in Africa, said DeSilva. "I can't image how they would have survived if they didn't go into the trees at night". However, there was something more that puzzled the researchers, in the first phase. "We conclude from this, and from previous studies on the shoulders of the Dikika child that she would have been able to climb, and to also grasp onto her mother during travel". "But, you work with what you have, and make adjustments as new fossils are inevitably discovered", DeSilva told Gizmodo.
Nonetheless, this discovery is unprecedented and "allows us to study the growth and development of our ancestors in a way we haven't", said DeSilva.