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.

Patterns of aquatic decay and disarticulation in juvenile Indo-Pacific crocodiles (Crocodylus porosus), and implications for the taphonomic interpretation of fossil crocodyliform material

“…(2) microbial mat formation (Hellawell and Orr, 2012;Schwermann et al, 2012;Iniesto et al, 2013), and (3) adipocere formation (O''Brien and Kuehner, 2007;Ubelaker and Zarenko, 2011;Schwermann et al, 2012). However, these stagnation scenarios do not account for the likelihood that even in low energy conditions, vertebrate carcasses may float and then disarticulate upon sinking.…”

Isotope compositions (C, O, Sr, Nd) of vertebrate fossils from the Middle Eocene oil shale of Messel, Germany: Implications for their taphonomy and palaeoenvironment

“…Anoxic bottom water along with a lack of bioturbation and reduced degradation by anaerobic microbes led to the undisturbed deposition of macrofossils of vertebrates at Messel (Schmitz, 1991;Schaal and Ziegler, 1992;von Koenigswald and Storch 1998;Franzen, 2007;Gruber and Micklich, 2007;Mayr, 2009;Joyce et al, 2012;Micklich, 2012;Schwermann et al, 2012;Smith and Wuttke, 2012), plants (Wilde, 1989(Wilde, , 2004Collinson et al, 2012) and invertebrates (Neubert, 1999;Wedmann, 2005), as well as microfossils such as pollen and spores (Thiele-Pfeiffer, 1988;Lenz et al, 2007Lenz et al, , 2011, algae (Goth, 1990;Lenz et al, 2007) and sponge spicules and gemmules (Richter and Wuttke, 1999;Richter and Baszio, 2009). The preservation of the fossils is exceptional with beetles still displaying structural colours (McNamara et al, 2012); feathers featuring preserved arrays of fossilised melanosomes, allowing reconstruction of the original colouration (Vinter et al, 2010); and plant macrofossils preserved as remnants of the original organic material in various stages of compression and degradation (Wilde, 1989;Collinson et al, 2012).…”

Patterns of Aquatic Decay and Disarticulation in Juvenile Indo-Pacific Crocodiles (Crocodylus Porosus), and Implications for the Taphonomic Interpretation of Fossil Crocodyliform Material

“…The benefit of actualistic taphonomy is that the time taken to progress through the five stages of vertebrate decay --(1) fresh, (2) bloated, (3) active decay, (4) advanced decay, and (5) remains (modified from Payne, 1965;Anderson and Hobischak, 2004;Cambra-Moo et al, 2008) --along with the level of skeletal articulation during these five stages, can be observed in real time, providing an "…empirical database of cause (taphonomic process) and effect (preservational bias)" (Allison et al, 1991, p. 78). A combination of relational analogies and actualistic taphonomy have been successfully used to interpret the taphonomic histories of fossil fish (Elder and Smith, 1984;Elder, 1985;Elder et al, 1988;Hellawell and Orr, 2012;Iniesto et al, 2013), reptiles (Brand et al, 2003a,b;Beardmore et al, 2012a,b;Meyer, 2012;Richter and Wuttke, 2012;Smith and Wuttke, 2012), mammals (Weigelt, 1989;Brand et al, 2003b;Noto, 2009;Behrensmeyer and Miller, 2012;Schwermann et al, 2012), and avian dinosaurs (Davis and Briggs, 1998;Brand et al, 2003b;Cruz, 2007;Faux and Padian, 2007;Prassack, 2011). Even with the potential pitfalls of assuming taphonomic uniformitarianism (see discussion in Gifford, 1981;Elder et al, 1988;Brasier et al, 2011), actualistic taphonomy can provide a more powerful analytical tool than analogical reasoning alone (Young, 1989;Denys, 2002;Noto, 2009).…”