Foot Bone Find a ‘Missing Link,’ Scientists Say : Evolution: Fossils discovered in South Africa may help pinpoint when human ancestors began walking upright.

South African scientists said Friday that they have found important new evidence revealing how humanity’s earliest ancestors started to walk upright.

In quarry rubble at the bottom of a cave at Sterkfontein, near Johannesburg, they unearthed the oldest known set of connected pre-human foot bones. Scientists say the bones, which apparently belonged to a creature that walked sometimes on all fours like an ape and at other times on two feet like a human, are about 3.5 million years old.

“Here in this one combination of four bones we have a real missing link,” said paleoanthropologist Ronald Clarke, who dubbed his find Little Foot. “It combines a human type of anklebone with apelike bones leading up to the big toe.”

Phillip Tobias, director of Witwatersrand University’s Palaeo-Anthropological Research Unit in Johannesburg, said the discovery may solve the dispute over whether early African hominids, as early pre-human primates are called, were adapted to walking upright on only two limbs (bipedal) or retained some tree-climbing features and sometimes moved on all fours (quadrupedal).

“The new foot bones, . . . comprising a row of articulating bones on the inner side of the foot that leads down to the great toe, provide the best evidence yet found on this question,” he said.

“Our studies of these foot bones show clearly that the early ape-man of Sterkfontein had a foot which equipped it to walk on two feet, as in humans, but also its big toe was highly mobile and was set at a wide angle to the toes as in apes,” he said. “It’s important because of the light it throws on the way in which the transition occurred from the quadrupedal gait of chimps and gorillas to the bipedal gait of humans.”

Standing earlier this week at a point about 100 feet deep in the cave, Clarke pointed to white bones protruding from the layer of red earth from which the Little Foot bones were unearthed by quarry workers in the 1920s.

The discarded rubble lay at the excavation site until the rocks were chipped up for fossils in 1980. But again, Little Foot was overlooked.

The four bones, about 2.8 inches in total length, were thought to be just animal bones and were kept in boxes until Clarke decided to look through them last September.

“First I found the perfectly preserved anklebone. When I looked some more I found the next bone perfectly fitting into the first. That in itself would have been a marvelous find. But then there were still two more. All of them belonging to the same chap.”