Early Bipedalism Confirmed - Archaeology Magazine Archive


Early Bipedalism Confirmed	May 27, 1998
by Angela M.H. Schuster

More than 38 new hominid fossils discovered at Kanapoi near Lake Turkana in northern Kenya confirm that our ancestors walked upright more than 4.1 million years ago. According to Meave Leakey of the National Museums of Kenya in Nairobi and her colleagues, the new finds belong to Australopithecus anamensis, the first 22 fossils of which came to light in 1995 (see "Earliest Bipedal Ancestor?", November/December 1995). Among the new finds are numerous teeth, mandible fragments, a humerus which resembles that of a chimpanzee, and a tibia that bears traits clearly associated with the human line.

"The species is quite primitive," says project paleontologist Alan Walker of Pennsylvania State University. "Its jaws are shaped more like those of a chimpanzee than those of a human, and there appear to be large differences between the sexes in both overall body size and dentition." According to Walker, the males have very large canine teeth, and the enamel on them is thinner than that found on the female specimens, a characteristic of male apes, who sharpen their teeth for use as weapons. "These finds demonstrate that all parts of the human body did not evolve simultaneously," adds Walker, "but rather in bits and pieces, much like a mosaic."

The fossils discovered in 1995 were found in two different layers of sediment, leaving it unclear whether whether the remains represented one or two species. "The fossils associated with geologically younger deposits were the most human looking, while those at deeper levels seemed more primitive," says Walker, "which led some of our colleagues to think we were dealing with two species. The new finds, recovered from layers of volcanic ash dated, using an argon40/argon39 method, to between 4.07 and 4.17 million years ago, confirm that we were dealing with a single species."

Leakey and her team believe that A. anamensis is the first of the australopithecines, intermediate in morphology and age between the more primitive 4.4-million-year-old Ardipithecus ramidus, discovered at Aramis, Ethiopia, in 1995 (see "Earliest Known Ancestor," March/April 1995), and the more advanced Australopithecus afarensis, best known by the 3.2-million-year-old female Lucy, discovered in 1974. Leakey and her colleagues published their findings in the May 7 edition of Nature.