African fossils flesh out humanity's past.

Scientists have announced the discovery of 2.5-million-year-old fossils in East Africa belonging to a new species in the human evolutionary family. The evolutionary status of the species, dubbed Australopithecus garhi, remains unclear, although it may represent an ancestor of the Homo lineage, to which modern humans belong.

The same 2.5-million-year-old sediment that yielded these fossils contains animal bones bearing the earliest known traces of butchery, reports a team headed by anthropologist Berhane Asfaw of the Rift Valley Research Service in Addis Ababa, Ethiopia. Either A. garhi or an as yet unknown but related species of that time used stone tools to remove meat and marrow from antelope and wild horse carcasses, the scientists assert.

The find signals an early shift to meat and marrow consumption for obtaining the energy needed to support long-range migrations of human ancestors, Asfaw and his coworkers contend in the April 23 SCIENCE.

"The development of stone-tool technology allowed for this dietary revolution," says team member Tim D. White of the University of California, Berkeley. "This is the earliest evidence of a key adaptation that let our ancestors spread beyond Africa."

A meager fossil record exists for human ancestors that lived from 3 million to 2 million years ago. Attempts to reconstruct their evolutionary relationships and pinpoint the roots of the Homo genus routinely trigger scientific disputes (see story, p. 267).

The new discoveries come from a site in Ethiopia's Middle Awash research area, where three desert valleys intersect. Beginning in 1996, team members found limb and skull fossils in soil located next to what was once an ancient lake.

The remains show novel combinations of anatomical traits, inspiring the species' designation as A. garhi. The word "garhi" means "surprise" in the language of Ethiopia's Afar people.

The new species possesses much larger teeth than Australopithecus afarensis, the species best known for the specimen called Lucy. A. afarensis lived in East Africa from 4 million to 3 million years ago. Much like A. afarensis, A. garhi's face projects forward and its small braincase features a crest.

Lower-body fossils from the Ethiopian site include a long, apelike forearm and a relatively long upper leg similar to that of later human ancestors. These finds have not been firmly assigned to the same species as the skull remains.

Analyses of volcanic ash just below the finds, bones of extinct animals found near them, and remnants of Earth's, magnetic signal trapped in soil layers at the site independently confirm the fossils' age.

Numerous bones of antelope and wild horses dating to the same time as A. garhi exhibit incisions made by stone tools during meat removal as well as breakage attributed to marrow extraction. Stone tools previously found at a nearby 2.5-million-year-old site were also probably used to extract marrow, the researchers suggest (SN: 4/15/95, p. 237).

Anthropologist Daniel E. Lieberman of George Washington University in Washington, D.C., calls the new finds "exciting," but he cautions that "it's still anybody's guess" as to the position of A. garhi in the human evolutionary family.