Rolling bones: A preliminary study of micromammal abrasion on different initial taphonomic stages

Abstract

The identification of transport process is key to interpret the palaeoecology, the dating and the site formation. Apart from dispersal and size/shape selection, bone abrasion by water and sediment is an acquired taphonomic modification that makes transport recognizable in bone assemblages. Previous experiments with rodent bones used non-digested bones or emphasized abrasion on teeth to distinguish abrasion from digestion. Experiments with large mammals included different types of taphonomically modified bones. Following this procedure, two main aspects are here studied for the first time. On the one hand, we have focused on small mammal humeri and femora, which are also used to characterize digestion. We have also included different initial states or types of bones, such as digested, weathered or fossil bones to observe differences in abrasion behaviour that may help interpreting processes of water abrasion. On the other hand, we propose an easy test methodology to quantify the amount of surface loss. The resulting index to quantify surface loss shows light changes on bones abraded by clay and silts, in contrast to a more rapid and intense rounding of the salient angles by gravels. The latest yields a greater rounding and, therefore, surface loss, statistically significant. Cancellous tissues appear exposed after 72 hours of abrasion on proximal ends of femora and distal ends of humeri, mimicking corrosion produced by digestion. In this paper we describe key traits and quantify surface loss to distinguish between digestion and abrasion in postcrania, more specifically on proximal femora and distal humeri.