Lucy, it turns out, had company — another prehuman that also walked, but spent more of its time in trees.
Until now, there was no proof of another human relative living about the same time as the species made famous by the Lucy skeleton. However, a fossil discovery reveals there was another creature about 3 million years ago and it gives new insight into the evolution of a key human trait — walking on two legs.
The creature came to light when an international team of researchers unearthed a partial foot in eastern Africa. Like Lucy, it walked upright, but had a grasping foot that it used to climb tree branches. Scientists said it is now clear that various human relatives experimented with upright walking.
“This is just another window into solving the problem of how we got from a primitive foot to the modern human foot,” said Bruce Latimer of Cleveland’s Case Western Reserve University, who helped discover the fossil remains.
Various hominin species have co-existed throughout human evolutionary history, but this is the first sign of another during Lucy’s time.
So what was this tree-climbing and ground-dwelling creature? Scientists don’t yet know, because no skull or teeth have been recovered to make a determination. However, it’s clear the foot did not come from Lucy’s species, Australopithecus afarensis.
It’s rare to find prehuman feet because bones are fragile and don’t preserve well. So US and Ethiopian scientists led by the Cleveland Museum of Natural History were excited when they excavated eight foot and toe bones in 2009 in the remote Afar region of Ethiopia, 48km north of where Lucy was discovered in 1974.
By analyzing the bone structure and dating the surrounding dirt, the team concluded the fragments came from the right forefoot of a human relative that lived 3.4 million years ago. While Lucy had humanlike feet, this creature was less advanced.
The discovery was detailed in yesterday’s issue of the journal Nature. The authors did not name the new species because they know so little about it.
“This find is the first good evidence that there was a second, different species lineage” at that time, said Tim White, director of the Human Evolution Research Center at the University of California, Berkeley, who had no role in the discovery.
The ability to walk upright is a key feature that separates humans from other great apes. That a different human relative ambled around the same period as Lucy suggests upright walking evolved more than once, scientists said.