Virtopsy of the controlled decomposition of a dormouse Eliomys quercinus as a tool to analyse the taphonomy of Heterohyus nanus from Messel (Eocene, Germany)

Abstract

Fossil vertebrate skeletons from subaquatic sediments display a melange of decomposition processes, compaction and diagenesis, which have to be discriminated for a detailed taphonomic analysis. The sequence of decomposition and disarticulation of skeletal elements is controlled intrinsically by the different resistances of soft tissues to decay, as well as extrinsically by temperature and oxygen availability. Water pressure has a significant influence on the extent of bloating caused by gases of putrefaction. Bloated carcasses float at the surface, or can refloat from the bottom of the water body (depending on the water pressure), where they can be moved by currents or wind. During the last decade, forensic radiographic examinations by computed tomography (CT; Virtopsy) have evolved into a new approach for actuopalaeontological experiments, which allow a continuous insight into the decay process. In order to elucidate the taphonomy of the apatemyid mammal Heterohyus, we investigated the controlled decay of a dormouse (Eliomys quercinus) carcass in detail, using high-resolution micro-CT. Taphonomic study of a fossil specimen of a Heterohyus nanus from Messel revealed that decomposition came to a premature halt, as indicated by the disarticulation sequence of the skeletal elements, which stopped after a while. Little information is available about internal decay processes affecting the coherence of the skeletal system. The results of the actualistic study were compared with the state of disarticulation of the fossil apatomyid. The combination of different indicators of the decomposition process, the lack of skeletal disintegration in Heterohyus and palaeo-environmental data lead to the assumption that Heterohyus went through an adipocere forming phase before embedding.