Taphonomic significance of sub-aerial transport of vertebrate fossils on steep semi-arid slopes



Burial and fossilization of terrestrial vertebrate remains may be a singular process, but is more likely to involve several phases of re-exhumation and sedimentary displacement, especially in arid environments. Each exhumation offers the opportunity for selective entrainment of sub-aerial slope processes which leave slopes-the principal collecting ground-impoverished of certain fossils and enriched in others. Fossil shape is shown to be a major determinant of displacement on steep slopes, with rod-like particles (e.g., limb-bones) and spheroids (e.g., joints and some vertebrae) vying for downslope evacuation at mean rates up to 1.85 m.a-1 and 1.14 m.a-1. Disc-and blade-like fossils (e.g., cranial fragments and scapulae) arc concentrated in the talluvium. Transport is shown to vary directly with size on steep slopes, but the relationship is confused by the complicated shapes of fossil material. The post-exhumation sub-aerial displacement of vertebrate fossils not only determines the constituents of a collection, so influencing palacoecological reconstruction, but reduces biostratigraphical resolution. Fossils of different shape are given stratigraphical (i.e. vertical) ‘aging rates’ (up to 0.47 m.a-1) that can be used as correction factors at frequently visited sites.Vertebrata, taphonomy, sub-aerial transport.