Hominid butchers and biting crocodiles in the African Plio-Pleistocene

Abstract

Zooarchaeologists have long relied on linear traces and pits found on the surfaces of ancient bones to infer ancient hominid behaviors such as slicing, chopping, and percussive actions during butchery of mammal carcasses. However, such claims about Plio-Pleistocene hominids rely mostly on very small assemblages of bony remains. Furthermore, recent experiments on trampling animals and biting crocodiles have shown each to be capable of producing mimics of such marks. This equifinality-the creation of similar products by different processes-makes deciphering early archaeological bone assemblages difficult. Bone modifications among Ethiopian Plio-Pleistocene hominid and faunal remains at Asa Issie, Maka, Hadar, and Bouri were reassessed in light of these findings. The results show that crocodiles were important modifiers of these bone assemblages. The relative roles of hominids, mammalian carnivores, and crocodiles in the formation of Oldowan zooarchaeological assemblages will only be accurately revealed by better bounding equifinality. Critical analysis within a consilience-based approach is identified as the pathway forward. More experimental studies and increased archaeological fieldwork aimed at generating adequate samples are now required.

Keywords: Oldowan; cutmarks; equifinality; taphonomy; zooarchaeology.

Fig. 1.

Bone surface modification marks on Pliocene hominid humeri from the Middle Awash study area, Ethiopia, visualized by photographs, SEM, and confocal microscopy. (A and B) The ∼4.2-Ma-old ASI-VP-2/420 distal humerus bears a jagged matrix-filled pit, shallow U-shaped grooves, and a long, straight score with snag pits at both ends. Straight, deep, V-shaped, intersecting linear marks with internal striae are illustrated. (C–I) The anterior surface of Maka humerus MAK-VP-1/3 exhibits linear bone modifications and bisected pits near its distal epiphysis. Note the presence of multiple internal striae and the deep, V-shaped profiles of most linear marks. Formerly thought diagnostic of cutmarks made by stone tools, such linear features are now known from crocodilian feeding experiments. Note that an interpretation of any one of these marks in isolation would lead to the impasse of equifinality described in the text. The anatomical, associational, geochronological, stratigraphic, and sedimentological contexts of these hominid fossils are interpreted as constituting a preponderance of evidence that the modifications are best attributed to crocodiles. F and G are casts. See text and SI Appendix, Figs. S4 and S5 for further details.

Fig. 2.

Fossilized crocodile teeth and inferred crocodile biting damage to a fossil equid tibia from the Hadar A.L. 339 Pliocene locality illustrate the potential and probable effects of ancient crocodile feeding on a large mammal carcass. (A) Line drawings of two small bone shaft fragments from Dikika inferred to be evidence of the earliest butchery with stone tools (1). (B and C) Unworn large and small fossil crocodile teeth from Hadar that exhibit anatomy capable of modifying bone surfaces during biting. Even individual teeth can feature dozens of raised and serrated enamel edges that can each produce cutmark and percussion mimics upon contact with bone surfaces. Crocodile biting can therefore leave a variety of marks on bones of prey, depending on the age, size, and taxon of the individual crocodile (SI Appendix, Fig. S2). (D and E) A fossilized equid tibia from Hadar with extensive surface modifications. Some marks on this specimen are indistinguishable from traces that have been produced experimentally with stone tools used for slicing and percussion. Note the presence of striae fields, pits with internal striae, extensive ectocortical flake scars, and V-shaped, internally striated linear grooves. Numerous bisected and rounded pits and punctures, drag-snags, and hook marks are more diagnostic of crocodile biting. In the context of the damage pattern observable across the intact limb bone, the most likely bone modification agent was crocodile. Absent the context of the intact specimen with its diverse modifications, smaller bone shaft fragments such as the Dikika ones remain subject to equifinality.

Fig. 3.

Bone surface modifications on ∼2.5-Ma-old fossilized ungulate bones from Bouri, visualized by photographs, SEM, and confocal microscopy. (A–E) The BOU-VP-11/14 bovid tibia showing numerous marks. (F–H) The BOU-VP-11/12 alcelaphine mandible exhibits long curvilinear marks across its posteromedial surface. Before experimental work on crocodile bite marks (refs. , , and and SI Appendix, Figs. S1 and S2), such deep, V-shaped, internally striated marks and forceful production of jagged pits with internal striae and large external cortical flaking were considered diagnostic of stone tool use by early hominids and differentiated from marks made by mammalian carnivores. However, even the limited currently available experimental data on crocodilians indicate that assessment of individual marks on small fragments drawn from inadequate samples of fossil bones (1) can be problematic. See text for a detailed consideration of the equifinality plaguing behavioral interpretation of such specimens and SI Appendix, Figs. S7–S13 for a broader consideration of spatial, stratigraphic, and taphonomic contexts.