Taphonomic comparison between large and small vertebrates in cave context (El Harhoura 2, Morocco): palaeontological, environmental and archaeological implications

Résumé En

Recent studies on macro-, meso- and microfaunas in Morocco contribute to obtain new information on the palaeoenvironmental changes during Late Pleistocene and Holocene in this region. Taphonomic analysis of the faunal assemblages allows to determine the origin of the accumulations and detect biases of faunal preservation. However, large and small vertebrates of same levels are rarely studied simultaneously despite the complementary taphonomic and palaeontologic information that they can provide. Because taphonomic agents may act differently on both small and large vertebrate bones, and the latter can be buried in the same times, we employed a comparative approach. We present here the results of the taphonomic studies made on macro-, meso- and microfaunas of the levels 1 to 8 of the El Harhroura 2 cave (Rabat-Témara, Morocco; Late Pleistocene-Holocene). We first attempt to recover the taphonomic histories of pre- and post depositional processes of all vertebrates in order to compare and discuss the different types of accumulations, as well as post-depositional processes having affected bones. At El Harhoura 2, in spite of anthropic marks on bones indicating sporadic human occupations, large carnivores (which have to be determined) seem to be the major accumulators of large mammals in almost all levels (except maybe Level 8). Remains belonging to mesofauna don’t present anthropic marks, but several traces attributed to non human predators. Concerning small vertebrates, they were mainly accumulated by owls (Bubo ascalaphus, Levels 1, 7, 8) and diurnal raptors and/or small mammalian carnivores (Levels 3, 6). In Levels 2, 4 and 5, an unknown predator or several predators could have simultaneously or successively accumulated small vertebrates. Thereby, a large range of predators seems to have occured all along the stratigraphy. Bones of large, medium and small vertebrates display light weathering traces (cracks, splitting, desquamation) and rare trampling striations, indicating a relatively quick burying (< 5 years). On the contrary, no rounding nor polishing by water were observed. Root marks are very numerous in all the material, but large mammal bones present a higher bias due to coating by sediments than for small vertebrate ones. Because of a lack of taphonomic referentials on north-african predators and post-depositional processes (weathering, burying) it is at present time difficult to characterise precisely the taphonomic biases and their impact on fossil communities. However, these biases are probably low and seem not to affect significantly the reliability of palaeoenvironmental reconstructions. Indeed, palaeoecological signals delivered by large and small mammals are very corroborating, indicating an alternation of arid (Levels 2, 5, 7) and relatively humid periods (Levels 1, 3, 4, 6, 8) at the end of the Quaternary in north-atlantic Morocco. We discuss these results at the light of a broader environmental and archaeological context in order to contribute to a better characterisation of the human occupations of this region.