Some 1.5 million-year-old footprints, found in sediment deposits in northern Kenya, are the oldest identified footprints since Mary Leakey found 3.75 million-year-old tracks preserved in volcanic ash in northern Tanzania. Those prints belonged to Australopithecus afarensis, and provided clear evidence of bipedalism.
"In a sense, it's like putting flesh on the bones," said John Harris, an anthropologist with the Koobi Fora Field School of Rutgers University. "The prints are so well preserved." Harris and other colleagues report in the Feb. 27 issue of the journal Science on finding several footprint trails within two sedimentary rock layers.
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.
William L. 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.
The footprints, dated to between 1.51 million and 1.53 million years ago, were discovered at Ileret, Kenya. With a large toe parallel to the other toes, the prints indicate a modern upright stride, the researchers said. They are likely to have been made by the early hominid Homo ergaster or early Homo erectus. This change in locomotive methodology brought with it a host of anatomical changes; our feet, knees, hip, spine, and even our skull all had to change to accommodate this mode of moving.
Footprints reveal a good deal about how a creature walks—they graphically illustrate the pressure distribution generated during a step or stride. Under normal walking conditions, there is a highly predictable movement and pressure distribution. Modern humans begin with our heel making the first contact with the ground; the pressure is then transferred along the outside of the foot, travels across the ball of our foot, and we finally push off using our big toe.
The lead researcher was Matthew R. Bennett of Bournemouth University in Britain. Others taking part included John W. K. Harris of Rutgers University and Brian G. Richmond of The George Washington University and the Smithsonian's National Museum of Natural History.
The authors of the paper conclude that "these prints add to the anatomical and archaeological evidence pointing to a major transition in human evolution with the appearance of hominids with long lower limbs, conferring advantages at a lower energetic cost, and archaeological indications of activities in a variety of ecological settings and the transport of resources over long distances."
