Faculty members from Case Western Reserve University's School of Medicine are members of a research team which discovered a new species of human ancestor called "Australopithecus garhi." Researchers found the 2.5 million-year-old fossils in the Bouri region of the Afar Desert of Ethiopia.
Scott W. Simpson and Bruce Latimer, both assistant professors in the medical school's Department of Anatomy, say that these fossils fill a major gap in our understanding of the dynamic evolutionary period of 2.5 million years ago -- the time our own genus, "Homo," first appeared.
Findings appeared in the the journal "Science." Simpson and Latimer were among authors of the research paper and were part of the team of paleontologists who conducted the fieldwork and analysis of the fossils. Latimer is also curator of physical anthropology and assistant director for science at the Cleveland Museum of Natural History.
Between 1996 and 1998, a partial cranium, a partial fossil skeleton, a jaw, and other fossils were found in 2.5 million-year-old lake margin deposits in Ethiopia. In addition to the hominid fossils, the oldest evidence of stone tool use was discovered when a series of battered and cut bovid and horse bones were uncovered.
The new species name, "garhi," means "surprise" in the local Afar language. Researchers chose "garhi" because the anatomy of this species was a surprise to them.
The hominid fossil record has few fossils between 2.9 million and 2 million years ago in East Africa. "We know what kind of species went into that period and what kind of species came out, so scientists created links, mentally, between what you started with and what you ended up with. This one caught us off guard. It has a combination of traits we did not expect to find," Simpson said.
A striking characteristic of "A. garhi" is the unique combination of a small brain and very large and unusually proportioned teeth. The partial skeleton is also notable for having a relatively long femur (thigh bone). The ratio in length of the humerus (upper arm bone) to the femur is identical to that found in modern humans. However, the length of the forearm is much longer than in modern humans and more similar in length to chimpanzees and gorillas.
This find demonstrates that the thigh elongated to modern human proportions by 2.5 million years ago, a million years before the forearm shortened. This ratio of the arm bone to thigh bone in "A. garhi" is markedly different from its short-legged immediate ancestor from 3.6 million to 2.9 million years ago -- "Australopithecus afarensis," popularly known as "Lucy."
In a companion paper, some members of the research team announce evidence that antelopes and horses were butchered with the world's earliest stone tools.
Evidence of large-mammal butchery shows that the earliest stone technologies were aimed at getting meat and marrow from large mammals. This signals a dietary revolution that may have eventually paved the way toward an invasion of new habitats and continents.
The co-directors of the research project are Berhane Asfaw of the Rift
Valley Research Service in Addis Ababa, Ethiopia, and Tim White of the
University of California at Berkeley.
Other members of the research team are Owen Lovejoy of Kent State
University and Gen Suwa of the University Museum at the University of Tokyo.
Journal
Science