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EXPERIMENTAL DECAY OF SOFT TISSUES !ROBERT S. SANSOM !Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, M13 9PT, UK <robert.sansom@manchester.ac.uk> ABSTRACT .ÑThe exceptionally preserved fossil record of soft tissues sheds light on a wide range of evolutionary episodes from across geological history. Understanding how soft tissues become hard fossils is not a trivial process. A powerful tool in this context is experimentally derived decay data. By studying decay in a laboratory setting and on a laboratory timescale, an understanding of the processes and patterns underlying soft-tissue preservation can be achieved. The considerations and problems particular to experimental decay are explored here in terms of experimental aims, design, variables, and utility. Aims in this context can relate to either reconstruction of the processes of soft-tissue preservation, or to elucidation of the patterns of morphological transformation and data loss occurring during decay. Experimental design is discussed in terms of hypotheses and relevant variables: i.e., the subject organism being decayed (phylogeny, ontogeny, and history), the environment of decay (biological, chemical, and physical) and the outputs (how to measure decay). Variables and practical considerations are illustrated with reference to previous experiments. The principles behind application of experimentally derived decay data to the fossil record are illustrated with three case studies: the interpretation of fossil color, feasibility of fossil embryos, and phylogenetic bias in chordate preservation. A rich array of possibilities for further decay experiments exists and it is hoped that the methodologies outlined herein will provide guidance and a conceptual framework for future studies. !INTRODUCTION !Fossils are old. At first, it would seem that they are so old that researchers would have no hope of experimentally investigating the patterns and processes of fossilization. After all, research proposals for projects on the scale of millions of years are unlikely to be awarded funding. Fossilization, however, is not a linear process with respect to time. The majority of anatomical change and loss occurs in the early stages in the formation of a fossil, after which little change generally takes place. These early stages can be experimentally investigated on a laboratory timescale ranging from hours to months. This is especially relevant to the exceptionally preserved soft-tissue fossil record. Non-biomineralized tissues such as cuticle, muscles, and nerves are lost to decay relatively quickly following death and as such, the soft anatomy of an organism is locked in a post-mortem race between decay and fossilization (Briggs, 1995). In those rare instances that preservation wins, the spectacular fossils that result shed unique and powerful light on a wide range of evolutionary events ranging from the Cambrian explosion of animal life to the origin of bird flight in dinosaurs (Briggs et al., 1994). Soft tissues, however, are extremely labile. They are never preserved as an accurate facsimile of the original organismÕs in-vivo anatomy in the way that skeletons can be; instead, they have been distorted and changed by the processes of decay and loss that are intrinsic to their fossilization. To make sense of exceptionally preserved fossil soft tissues, we need an understanding of the processes that led to their formation and how the data they provide might have been transformed by their formation. In fact, it is difficult to interpret this class of fossils without experimentally derived data. This review will discuss how experimental taphonomy aims to unlock both the processes and patterns of decay, i.e., the processes that make it possible for soft tissues to become part of the fossil record and the patterns of data loss and transformation that can occur during fossilization. The nature of experimental design and the multitudinous variables involved in taphonomic experiments are also addressed. Finally, examples are used to illustrate how the findings of taphonomic experiments can be applied to paleontological data, and in some instances, transform our interpretation of fossils. In: Reading and Writing of the Fossil Record: Preservational Pathways to Exceptional Fossilization. The Paleontological Society Papers, Volume 20, Marc Laflamme, James D. Schiffbauer, and Simon A. F. Darroch (eds.). The Paleontological Society Short Course, October 18, 2014. Copyright © 2014 The Paleontological Society.
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