Taphonomy and palaeoecology of an assemblage of large mammals: Hyaenid activity in the Lower Pleistocene site at Venta Micena (Orce, Guadix-Baza Basin, Granada, Spain)

Abstract

We report taphonomic and palaeoecologic data on the rich, diverse and well preserved assemblage of large mammals from lower Pleistocene deposits at Venta Micena (Orce, Granada, south-east Spain). The biostratinomic and diagenetic characteristics of the assemblage are congruous with the sedimentary context deduced from the study of the site, and both confirm that: (i) the assemblage represents an accumulated taphonomic stage, (ii) it was formed by demic, autochtonous palaeobiologic entities, which were preserved and recorded in situ, and (iii) it is the result of biological processes and agents. Interspecific analysis of size/abundance patterns in ungulates shows that the main taphonomic bias affecting the bones was produced by biological destruction before burial, and that the loss of information was greater for species of smaller body size. Factor correspondence analysis was used to compare the frequencies at which some groups of postcranial elements are represented in several recent and archaeological bone assemblages accumulated by carnivores, rodents and hominids. The results obtained strongly suggest that the bones from Venta Micena were collected mainly by hyaenids, which deposited them near shallow dens excavated around the ponds that surrounded the Pleistocene lake of Orce. An analysis of the abundance of major long bones has shown that differential fragmentation was produced by hyaenas as a function of their structural density and mean marrow content. All these data allow to formulate a descriptive-quantitative model for the characterization of bone assemblages generated from hyaenid activity, in which Venta Micena is an example of bone concentration and modification activities by Pachycrocuta brevirostris. Strong selection of prey by carnivores (which killed preferably juveniles, females and individuals with diminished locomotive capabilities among ungulate prey species of larger body size) is indicated by (i) the abundance of juvenile individuals with deciduous teeth in relation to the average weight estimated for adults in each ungulate species, by (ii) the U-shaped attritional mortality profiles deduced from crown heigth measurements, by (iii) the presence of many metapodials with different osteopathologies, and by (iv) a biased sexual ratio deduced from the metacarpals of large bovids. Comparison between the frequencies in which modern African carnivores kill and scavenge ungulates from different size classes and the abundance of these size categories in the assemblage suggests that the Venta Micena hyaena was a bone-cracking scavenger which fed largely on carcasses of ungulates preyed upon and partially consumed by flesh-eating carnivores such as saber-toothed felids and wild dogs.