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Foot fossil suggests ancient human ancestor had feet like an ape

March 29 (): A fossil unearthed in the Ethiopian desert resembles feet belonging to Ardipithecus ramidus, a species thought to have roamed East Africa a million years before 3.2 million year-old Lucy skeleton and other members of her species, Australopithecus afarensis.

The fossilised bones are dated to be 3.4 million years old. Studying these foot fossils, scientists have obtained a fascinating new insight into the evolution of humans and our ability to walk.

The fossil foot appears to settle the long-disputed question of whether there was only a single line of hominins — species more closely related to humans than to chimpanzees — between four million and three million years ago.

The researchers say they do not have enough remains to identify the species of hominin, or human ancestor, from which the right foot came. But just the shape of the bones shows the creature could walk upright at times.

But they say the foot was strikingly similar to the earlier hominin Ardipithecus ramidus, nicknamed Ardi, which lived 4.4 million years ago, in what is now Ethiopia. Ardi’s foot also had a divergent big toe, similar to those of apes and gorillas, for tree climbing, though Ardi was an occasional upright walker.

The Lucy species had long before evolved almost humanlike upright walking, bipedality, as attested by the Laetoli footprints in Tanzania from as early as 3.7 million years ago. This other species was still built for climbing trees and grasping limbs. It was capable of walking, though less efficiently and probably with an awkward gait.

The new found foot not only belonged to a different species but also had evolved a distinctive mode of locomotion, which scientists described as “equivocal.” It clung to the trees and never adapted to terrestrial mobility outright.

But the fact this creature could and would walk on the ground is evidenced by the nature of the bone joints. These were arranged such that the foot could push off, or toe-off – something only humans do as they walk, and something flat-footed apes cannot achieve.

Still, more bones are needed to get a better sense of how this creature travelled, scientists said.

“You want the rest of the foot,” said Daniel Lieberman, a paleoanthropologist at Harvard University who was not involved in the study. “We also need to do research and understand what these variations mean for performance. … How did these animals walk?”

For now, the scientists can’t say for sure that this foot belonged to an A. ramidus because species classifications are determined by looking at skulls, not feet.

“You have to go back and find more fossils,” Latimer said. “It’d be beautiful to find a skull or a jaw or a knee or a hip. Any of these things will tell us more about this animal.”