Australopithecus garhi: A New Species of Early Hominid from Ethiopia

Summary of article appearing inScience Vol.284; 23 April, 1999

Article by B. Asfaw, T. White, O. Lovejoy, B. Latimer, S. Simpson, and G. Suwa.

From the Awash region of Ethiopia, a new species of early human was recovered by a University of California at Berkeley excavation in the field seasons of 1996 and 1997. The most important of the finds came on November 20, 1997, when the partial cranium BOU-VP-12/130 was found, although numerous fossils from other individuals of the same species were also recovered it the same basin. The species has been named Australopithecus garhi due to its surprising morphology ("garhi" means surprise in the local Afar language). The sediments in which the fossils were found have been dated to roughly 2.5 million years ago.

Australopithecus garhi is distinguished from other species of Australopithecus, by its unique combination of dental and facial features. The cheek teeth are absolutely larger than Australopithecus afarensis, and can be said to be "megadont" (see the Robust Debate). However, Australopithecus garhi lacks derived characters of the robust early human lineage, leaving it as a sister taxon to the gracile forms. The morphology of the face retains primitive characteristics of Australopithecus afarensis to the exclusion of Australopithecus africanus. It is believed that Australopithecus garhi is part of the eastern African lineage descended from A. afarensis. The cranial capacity of the partial skull has been estimated at 450 cc. (under such Australopithecine individuals such as Mrs. Ples but slightly larger than modern chimpanzee capacities). However, aspects of the dentition are very similar to early specimens of the genus Homo. Postcranially, the A. garhi material shows human-like ratios for femur to humerus length (but see OH 62!) while retaining ape-like proportions for the length of the forearm to the upper arm (the brachial index). Thus, BOU-VP-12/130 and the associated material show a strange admixture of traits recalling earlier A. afarensis and traits pointing toward later Homo.

This would place Australopithecus garhi very close to the origination point of our genus. The authors argue that Australopithecus garhi may represent the evolutionary step between A. afarensis and Homo. It possesses derived traits that are seen in Homo, yet it is most definitely not related to A. africanus. The authors would now place A. afarensis as the stem of a radiation that would include both Paranthropus aethiopicus and Australopithecus garhi, the former leading to the robust Paranthropus boisei and possibly P. robustus, the later leading to early Homo. This would make A. africanus a dead-end branch of the human lineage.

The authors also note that further consideration may actually place Australopithecus garhi within the genus Homo at a later date, but at this time they have chosen to stay with a conservative classification, noting its small cranial capacity, and prognathic Australopithecine face. In other publications on the finds, the authors identify evidence for use of tools in associated sediments. Bones were found with evidence of cut marks and damage indicative of being smashed open for the marrow inside. An assemblage of stone tools was also found. The link between Australopithecus garhi and the tool use is still unproved, but it is interesting to note that tool use may precede increase in brain size in early human evolution.

The combination morphological ape-like and human-like traits and the possible association with tool use make Australopithecus garhi has thrown many of the notions of human evolution into question.

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