An experimental study of large mammal bone modification by crocodiles and its bearing on the interpretation of crocodile predation at FLK Zinj and FLK NN3

摘要

The taphonomic signature of crocodiles as agents of bone modification has been previously identified by specific tooth mark types (e.g., bisected pits) and by a conspicuous presence of these marks: more than 75% of bones modified by crocodiles bear at least one of these distinctive marks. Therefore, crocodile tooth-marking would be notably prevalent in bone assemblages resulting from crocodile predation and active scavenging. The present study contributes to refine this diagnosis by showing greater variability of these types of marks, a different degree of tooth-marking intensity, and a somewhat different distri-bution of tooth-marked elements according to skeletal parts from previous experiments with crocodiles. Some of these differences are due to different experimental variables and conditions and this highlights the need to understand behavioral variability in crocodile ecological settings. This variability in crocodile tooth-marking probably results from several as-yet-inadequately measured behavioral and ecological factors, such as intensity of feeding competition and differences between male and female crocodile feeding behaviors, among others. Furthermore, this study also contributes to a better definition of the microscopic criteria that can be used to distinguish crocodile-inflicted marks from other types of bone surface modifications. In light of these and previous experimental frameworks, we reevaluate the application of these analogs to modifications documented in hominin fossils from Olduvai Gorge (OH8 and OH35) and the resulting inferences about the hazard posed by crocodiles on the paleolandscape where FLK North North and FLK Zinj (Bed I) were formed. The taphonomic analysis also shows that Olduvai OH8 and OH35 were probably not preyed upon by crocodiles. It is concluded that no tangible evidence can be used to support the interpretation that OH35 was modified by crocodiles and that the overall presence of crocodiles in FLK North North and FLK Zinj was rather marginal, based on the virtual absence of crocodile-modified bones in both archaeofaunal assemblages.