Early hominid rises again.

Fossils unearthed in Kenya between 1995 and 1997 come from a recently identified species in the human evolutionary family that lived about 4.1 million years ago, a research team reports. The creature, dubbed Australopithecus anamensis, was the earliest known human ancestor capable of walking upright.

A. anamensis was first identified from 21 fossils found at two sites near Lake Turkana (SN: 8/19/95, p. 119). An additional 38 specimens from the same locations now flesh out this ancient hominid's mix of chimplike and humanlike features, according to paleontologist Meave G. Leakey of the National Museums of Kenya in Nairobi and her coworkers.

Age estimates for A. anamensis derive from measurements of argon isotopes in crystals removed from volcanic ash that brackets the fossil-bearing sediment. The fossils, which were buried in an upper and a lower soil layer, all date to approximately 4.1 million years ago, Leakey's group reports in the May 7 Nature. Preliminary age estimates for the material ranged from about 4.2 million to 3.8 million years old.

A. anamensis jaw and teeth remains look more like those of chimps than of modern humans, the scientists contend. A wrist bone attributed to the ancient hominid also suggests a chimplike arrangement of the hand and fingers. Large differences in body size and canine tooth shape between A. anamensis males and females appear comparable to those observed in modern gorillas, they add.

However, previously uncovered leg fossils indicate that A anamensis walked upright, a key trait of hominids.

Leakey's group theorizes that the hominid fossil record from nearly 4.5 million to just after 3 million years ago may consist of a single population that began as a separate genus, Ardipithecus, which evolved into A. anamensis and then A. afarensis, the species that includes the partial skeleton of Lucy.

The new fossil finds help to confirm the existence of A. anamensis as a separate species that inhabited eastern Africa before the emergence of Lucy's kind, remarks anthropologist Peter Andrews of the Natural History Museum in London.

A planned analysis of Ardipithecus fossils, which has been slowed by the difficulty of removing surrounding rock from the specimens, may clarify the evolutionary relationship between Ardipithecus and A. anamensis, he says.