Maker of 1.5 million-year-old African footprints had a modern gait

By John Noble Wilford
The New York Times Media Group
International Herald Tribune

Footprints uncovered in Kenya show that as early as 1.5 million years ago an ancestral species, almost certainly Homo erectus, had already evolved the feet and walking gait of modern humans.

An international team of scientists, in a report published Friday in the journal Science, wrote that the well-defined prints in an eroding bluff east of Lake Turkana "provided the oldest evidence of an essentially modern humanlike foot anatomy" and added to the picture of Homo erectus as the prehumans who took long evolutionary strides - figuratively and, now it seems, also literally.

Where the individuals who made the tracks were going, or why, is beyond knowing by the cleverest scientist. The variability of the separation between some steps, researchers said, suggests that they were picking their way over an uneven surface, muddy enough for leaving a mark as an unintended message from an extinct species for the contemplation of its descendants.

Until now, no footprint trails had ever been associated with early members of our long-legged genus Homo. Preserved ancient footprints of any kind, sometimes called
"fossilized behavior," are rare indeed.

The only earlier prints of a protohuman species were found in 1978 at Laetoli, in Tanzania. Dated at 3.7 million years, they were made by Australopithecus afarensis, the diminutive species to which the famous Lucy skeleton belonged. The prints showed that the species already walked upright, but its short legs and long arms and its feet were in many ways apelike.

Studying the more than a dozen erectus prints, scientists determined that the individuals had heels, insteps and toes almost identical to humans, and that they walked with a long stride similar to human locomotion.

The researchers who made the discovery, as well as independent specialists in human origins, said the prints helped explain fossil and archaeological evidence that erectus had adapted the ability for long-distance walking and running. Erectus skeletons from East Asia revealed that the species, or a branch of it, had migrated out of Africa as early as 1.8 million years ago.

The lead author of the journal report was Matthew Bennett, a dean at Bournemouth University in England, who analyzed the prints with a new laser technology for digitizing their precise depths and contours. The tracks were excavated over the last three years by paleontologists and students directed by John Harris of Rutgers University in collaboration with the National Museums of Kenya.

Daniel Lieberman, a professor of biological anthropology at Harvard who studies the evolution of human locomotion but was not a member of the research group, said the prints established what experts had suspected for some time. Erectus, he said, "probably looked much like us, both walking and running over long distances."

Although the discoverers were cautious in attributing the prints to Homo erectus, Lieberman and other experts said in interviews that it was highly unlikely they could have been made by other known hominid contemporaries.

"The prints are what you would expect from the erectus skeleton we have," said Leslie Aiello, president of the Wenner-Gren Foundation for Anthropological Research, which supported the research. "We are seeing erectus in motion," she added.
William Junger, a paleoanthropologist at Stony Brook University in New York, said the footprints were further evidence that erectus had "undergone a major structural change in body plan, and it's much like our own."

One obvious exception: the erectus brain, though advanced from previous ancestors, was still well below the size of the Homo sapiens brain.

No erectus foot bones have yet been found anywhere, but other well-preserved skeletons showed the species to be taller, less robust than earlier hominids.