Australopithecus garhi, A New Human Ancestor?
A possible human ancestor and the earliest traces of animal butchery were reported from Ethiopia in April of 1999. The discoveries come from Bouri, in the Middle Awash area in the Afar desert of Ethiopia, about 70 km. south of the Lucy A. afarensis discovery at Hadar. The fossils and associated faunal remains date to 2.5 mya. The fossils were dated by the argon-argon method. Anthropologist Berhane Asfaw and colleagues described the fossils in the April 23, 1999, issue of Science. In companion articles, Giday Wolde Gabriel and his colleagues described the paleoenvironment and the geology. The research team reported evidence that antelopes were butchered with the world's earliest known stone tools. There is no direct evidence that A. garhi used stone tools, but the proximal cutmarked bones provide circumstantial evidence.
A. garhi may represent an evolutionary link between the genera of Australopithecus and Homo. It is probably descended from A. afarensis and adds a potential ancestor for the genus Homo. The remains are from the time when there are very few fossils, between 2.0-3.0 mya.
Tim White found the first of the key fossils in 1996 near the Afar village of Bouri. He noticed an arm and leg on a low hill. Excavation at the site produced pieces of a partial skeleton and antelope bones with stone tool marks. Nearby, in 1997, Yohannes Haile-Selassie found the exposed skullcap of the type specimen of Australopithecus garhi. "Garhi" means "surprise" in Afar. The anatomical features of the specimen were a surprise to the investigators. Cranium fragments had scattered down the slope. The researchers recovered a virtually complete upper jaw and skull fragments. Six additional hominids belonging to A. garhi were found, along with thousands of animal fossils.
The fossils were found in an undescribed geological strata. Geologists named the formation the Bouri Formation. They described three stratigraphic subunits, the Herto, Daka and Hata members. A. garhi is from the Hata Member, from sediments near an ancient lake. Unlike today's harsh desert, 2.5 mya herds of antelope grazed the plains surrounding a lake. Volcanic ash and lava are interbedded with the fossil bearing strata, providing accurately datable material. The ash just below the fossils erupted 2.5 mya according to argon-argon dating.
The type specimen is ARA-VP-12/130, an associated set of cranial fragments,
frontal, parietals, and maxilla with dentition. The teeth are larger
than those of the earlier A. afarensis. Its braincase, face and
palate are more primitive than those of later Homo. The known
specimens demonstrate that the thigh bone had elongated a million years
before the Homo forearm shortened. The derived human-like humeral/femoral
ratio together with the ape-like upper arm to lower arm ratio evidence
the mosaic-like evolution of the features that characterize modern humans.
Archaeologist Sileshi Semaw discovered the world's earliest stone tools, at 2.5 mya, from nearby Gona. That location did not evidence what the tools were used for. The faunal remains at Bouri provide an answer to the question and identify A. garhi as the possible toolmaker at Gona. The excavated antelope fossils have cutmarks made by stone tools and some were opened by hammerstones. The new findings evidence use of meat and marrow, high quality dietary resources that probably improved survivability, at an early date.
McHenry, Henry M., Lee R. Berger. 1998. Body proportions in Australopithicus afarensis and A. africanus and the origin of the genus Homo. Journal of Human Evolution 35, 623-651.
Sanders, Robert. 1999. Earliest evidence of animal butchery, new species of human ancestor, found in Ethiopia's Afar desert. http://www.urel.berkeley.edu/urel_1/CampusNews/PressReleases/releases/4-19-1999z.html