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Silicified wood is one of the most frequent and insightful records of ancient life since the Devonian. Although cellular anatomy is often preserved in great detail, alterations of organic matter occur during fossilisation modifying tissue properties. Due to taphonomic pathways, plant tissues experience multiple changes, which may cause a tissue-volume reduction, including desiccation, microbial decay, charcoalification, coalification and mineralisation. Case studies from different geological ages, fossilisation backgrounds and palaeogeographic positions provide evidence of widely distributed but still underestimated shrinkage phenomena in fossil woods. Samples from seven Paleozoic to Cenozoic localities representing several geologic settings are analysed to understand putative shrinkage reasons. Volume reduction is more widespread in fossilised wood than commonly thought. Accordingly, quantitative data on cellular anatomy 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 lacking tracheid secondary walls and decayed tissue constituents. Differential shrinkage of silicified wood and their encrustation by stromatolites help quantify volume loss during fossilisation. They provide graphically measurable, one- and two-dimensional parameters to assess percental volume loss. Our approach reveals essential shrinkage-related alterations independent of palaeoenvironment, plant material and host rock. Tissue contraction varies considerably: Unexpectedly, variability even occurs in wood from the same fossil site, the same strata and reflecting the same taphonomy. The results demonstrate that shrinkage needs to be taken into account in comparisons of morphometric data obtained from fossil and modern woods, irrespective of their particular provenance. |
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