Fossilised remains of a partial foot has led scientists to speculate that there were several species of pre-humans living in Africa at the same time.
What's more, researchers believe these different species had their own way of walking.
The discovery of eight bones from an unknown species of hominin in the central Afar region Ethiopia by a team from the Cleveland Museum of Natural History is reported today in the journal Nature.
"What is neat about this work is that it has a mixture of features that add to a picture that's been emerging over the last few years that the evolution of bipedalism and the evolution of human locomotion has been very complicated and diverse," says Dr Daniel Lieberman, a professor of Human Evolutionary Biology at Harvard University and author of a commentary also appearing in Nature.
"On the one hand the foot has a very divergent big toe, a bit like a chimpanzee. So it was probably very good at grasping and climbing trees."
"But on the other hand the joints between what are called the metatarsals and the phalanges where the base of the toes are, are what we call canted and upright so that they basically look like humans."
"So we have a creature that was walking, clearly, but also very good at climbing and it's the same age as more modern feet of Australopithecus."
Australopithecus afarensis is better known as Lucy - named after the remains that were also found in Ethiopia almost 40 years ago.
"Lucy had ... a big toe that was much more like ours. It was much more in line with the rest of the toes. She didn't walk like us but she had a much more modern gait than this creature," says Lieberman.
Lieberman believes this latest fossil find is part of a series of evolutionary steps in bipedalism, which began as far back as six million years ago.
"Maybe around four million years ago, the Australopith kind of foot evolved. And then sort of the final major stage I think in the evolution of the foot occurred around two million years ago with the origins of the species Homo erectus," he says. "Once you get Homo erectus you begin to get really modern human-like feet."
The find also raises the prospect that there were several pre-human species living in Africa at the same time
"We look around the world today and we see only one species of human. We think it's normal for there to be only one species. But of course it's not normal," says Lieberman.
"For most of human evolutionary history there have been plenty of different kinds of human species living at any one time. If you were to live 50,000 years ago, there would be humans and Neanderthals and maybe even other species living at that time.
"That certainly was the case if you went back a few million years. So we are just finding more fossil evidence of that diversity."