The fossil, known as “Selam,” is from the same species as the famous Lucy fossil, and was found in the same vicinity. The popular press erroneously labeled it “Lucy’s baby,” though Selam lived more than 200,000 years before Lucy.
In studying the fossil foot’s remarkably preserved anatomy, the research team reconstructed what life would have been like years ago for the toddler, and how our ancestors survived. They examined how the foot would have been used, how it developed, and what it tells us about human evolution.
“For the first time, we have an amazing window into what walking was like for a two-and-a-half-year-old more than three million years ago,” said Jeremy DeSilva, associate professor of anthropology at Dartmouth College and lead author of the study, published in Science Advances. “This is the most complete foot of an ancient juvenile ever discovered.”
The fossil record indicates that these ancient ancestors were quite good at walking on two legs. “Otherwise, if you are a bad upright walker, you are going to get eaten by leopards and go extinct,” DeSilva said.
At two-and-a-half years old, Selam was already walking on two legs too, but there are hints in her fossil foot that she was still spending time in the trees and hanging onto her mother as she foraged for food. Based on the skeletal structure of the child’s foot, specifically a more movable big toe which allowed them to grasp branches and climb, the kids probably spent more time in the trees than adults.
This lasting ability to climb gave the younger, more vulnerable juveniles a backup plan to walking.
“If you were living in Africa three million years ago without fire, without structures, and without any means of defense, you’d better be able get up in a tree when the sun goes down,” DeSilva said.
The new findings give researchers greater insight into the workings of evolution, not just in human ancestors but in general.
“These findings are critical for understanding the dietary and ecological adaptation of these species and are consistent with our previous research on other parts of the skeleton, especially the shoulder blade,” Alemseged said.
“Placed at a critical time on the cusp of being human, Australopithecus afarensis was more derived than Ardipithecus, a facultative biped that walked on two legs some of the time, but not yet an obligate strider like Homo erectus," he added. "The Dikika foot adds to the wealth of knowledge on the mosaic nature of hominin skeletal evolution.”
—Story first appeared on the UChicago Medicine website.