SYSTEMATIC ASSESSMENT OF A MAXILLA OF HOMO FROM HADAR, ETHIOPIA

The Hadar site in Ethiopia is a prolific source of hominid fossils att ributed to the species Australopithecus afarensis, which spans the per iod 3.4-3.0 million years (myr) in the Sidi Hakoma, Denen Dora and low er Kada Hadar Members of the Hadar Formation. Since 1992 a major focus of field work conducted at Hadar has centered on sediments younger th an 3.0 myr, comprising the bulk of the Kada Hadar Member. Witnessing t he rise of the ''robust'' Australopithecus clade(s), the origin of Hom o, and the first record of lithic artifacts, the period between 3.0 an d 2.0 myr is strategically vital for paleoanthropology. However, in ea stern Africa it is a particularly poorly sampled temporal interval. Th is paper provides a detailed comparative description of a hominid maxi lla with partial dentition found at Hadar in 1994. The specimen, A.L. 666-1, derives from a lithic artifact-bearing horizon high in the Kada Hadar Member, 0.8 m below the BKT-3 tephra, dated by the Ar-40/Ar-39 method to 2.33 +/- 0.07 myr. Our preliminary investigation of the homi nid specimen showed unambiguous affinities with early representatives of the Homo clade (Kimbel et al. [1996] J. Hum. Evol. 31:549-561). Fur ther studies on maxillary and dental morphology lead us to attribute A ,L. 666-1 to Homo aff. H. habilis. The new Hadar jaw is the first pale ontological evidence for the projection of the H. habilis maxillofacia l morphotype well back into the Pliocene. It may represent a male of t his species, whose maxillary hypodigm consists chiefly of females. A s ubsidiary finding of our study is that of the three earliest recorded species of Homo (H. habilis, H, rudolfensis, H. erectus), it is H. hab ilis that exhibits facial morphology closest to that expected in their last common ancestor. (C) 1997 Wiley-Liss, Inc.