Format: ORAL

Ronny Roessler

1 Museum für Naturkunde Chemnitz, Moritzstraße 20, D-09111 Chemnitz, Germany, roessler@naturkunde-chemnitz.de 2 TU Bergakademie Freiberg, Department of Palaeontology, Geological Institute, Bernhard-von-Cotta-Straße 2, 09599 Freiberg, Germany

Fossil wood belongs to the most frequent and insightful records of ancient terrestrial life. Although cellular anatomical preservation often provides excellent detail, various alterations of organic matter occur during fossilisation and modify tissue properties. Due to manifold taphonomic pathways, plant tissues experience multiple changes, which may cause a tissue-volume reduction, including desiccation, microbial decay, charcoalification, coalification and mineralisation. A few case studies concerning different geological ages, preservational backgrounds and palaeogeographic occurrences offer evidence of widely distributed but vastly underestimated shrinkage phenomena in fossil woods. Samples from several Paleozoic to Cenozoic fossil lagersttten representing diverse geologic settings are analysed to comprehend putative shrinkage reasons. As a result, volume reduction is more widespread in petrified wood than commonly thought and not easy to recognise. Unexpectedly, tissue contraction varies even in wood from the same fossil site, the same strata and reflecting the same taphonomy. Accordingly, quantitative data on cellular anatomy gained as a routine may be misleading, and cell size and shape modifications affect morphometric purposes, like the interpretation and identification of fossil species. Differences in preservation demonstrate the profound effects of microbial degradation, such as lack of tracheid secondary walls and decayed tissue constituents. Differential shrinkage of silicified wood and stromatolite encrustation help quantify shrinkage by providing graphically measurable, one- and two-dimensional parameters to assess percental volume loss during fossilisation. This study reveals essential shrinkage-related alterations independent of palaeoenvironment, plant material and host rock. The results demonstrate that shrinkage must be considered when comparing fossil and modern wood morphometric data.