Competing hypotheses about the timing and nature of hominid and carnivore contributions to the formation of the Plio-Pleistocene bone assemblage from FLK Zinjanthropus are tested. The hypotheses advanced by Bunn (1986; Bunn and Kroll, 1986) and Leakey (1971), and by Binford (1981, 1986) are tested using the proportion of long bone specimens bearing hammerstone percussion marks and carnivore tooth marks. Unambiguous test implications based on surface mark frequencies are provided by results of well controlled experiments and naturalistic observations that model three alternative sequences of long bone processing and consumption by hominids and/or carnivores. Percussion mark and tooth mark frequencies, reported systematically for the first time on the assemblage from FLK Zinjanthropus, allow the rejection of the hypothesis that carnivores rather than hominids at FLK Zinjanthropus enjoyed first access to marrow in long bone cavities. This result contradicts Binford's characterization of Plio-Pleistocene hominids as marginal scavengers of carcasses heavily ravaged by bone-crunching carnivores. However, a high proportion of tooth-marked long bone midshaft fragments allows the rejection of the alternative hypothesis that carnivore access to long bones was exclusively or even primarily secondary to butchery and marrow extraction by hominids, as argued by Bunn (1986; Bunn and Kroll, 1986) and Leakey (1971). The results show that the sequence of carnivore and hominid access to long bones, and their respective carcass tissue yields, was more complex, as is consistent with a dominantly passive scavenging mode of carcass acquisition by hominids hypothesized earlier on the basis of skeletal part data and paleoecological considerations. Confidence in these deductions based on surface mark frequencies is increased by demonstrations of (i) a close comparability in agencies of bone fragmentation between the control samples and FLK Zinjanthropus; (ii) the representativeness of the control samples with respect to the process-pattern relationship between marrow/grease extraction and frequencies of surface marking; and (iii) the energetic and mechanical uniformities linking rates of bone surface marking to the timing of carnivore and hominid access to long bone nutrients. (C) 1995 Academic Press Limited
