Rodents, rabbits and pellets in a fluvial terrace (PRERESA site, Madrid, Spain)

The aim of this work is to study from a taphonomic view the small mammals assemblage located on the Pleistocene site known as PRERESA. The small mammal fossiliferous layer is a silt level located at a fluvial terrace. The samples studied included remains from rodents (Minimum Number of Elements: MNE = 373) and lagomorphs (MNE = 372). During the excavation seasons, a distinct high concentration of small mammals was recovered apart, named as fossil ‘pellet’. We consider this ‘fossil pellet’ to be an aggregation of several pellets and it has been taphonomically analyzed apart and included in this study. The presence of such concentrations/aggregations is uncommon in this type of open-air sites. This aggregation contains 253 MNE fossil bones. The taphonomic study has considered three main aspects: anatomical representation, fragmentation, and corrosion by digestion. Due to the location of the site on a fluvial system, transport effects and abrasion were analyzed as well. The results obtained show a high representation of cranial elements (especially lagomorphs) as well as a high fragmentation of both cranial and postcranial elements. Digestion observed in this assemblage affects dental remains below 30% in both rodents and lagomorphs, being light and moderate digestion the most frequent degrees, but all samples reach extreme grades of digestion (in molars < 3%). Transport was analyzed using Voorhies groups (1969). All groups were present, even the easiest to transport. Group III (cranial remains) was the best represented. The simultaneous presence of all Voorhies groups suggests a low or null rate of transport. Results could indicate that the small mammal assemblage of PRERESA were produced by a nocturnal raptor, most likely an Eagle owl (Bubo bubo), whose nest or roosting site was installed near the fluvial channel.