Deuterostome decay - taphonomic testing of fossil anatomy and phylogenetic placement

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Questions of how, when and why our earliest fish-like ancestors evolved are fundamental to understanding our place in evolution, but answers remain elusive because the fossil record of these events is hard to read. We will address this problem by investigating how the bodies of our primitive animal relatives change as they decay, shedding new light on controversial fossils that contain important clues to our own deep ancestry.We, and all other animals with backbones, are classified as chordates, and sit together with some rather less familiar animals (sea squirts, acorn-worms, pterobranchs) on a major branch of the Tree of Life known as deuterostomes. This project will address a fundamental evolutionary question: what were our earliest chordate ancestors like, and how did they differ from their nearest deuterostome relatives? The principal difficulty in answering this question is understanding the early deuterostomes: after more than 500 million years of evolution, all the living groups of deuterostomes have modified their bodies in ways that make them quite different to one another. The evolutionary branches that sit between the living groups are all extinct, so the anatomically intermediate animals - which can lead us back down the evolutionary tree to those early ancestors - can exist only as fossils. Unfortunately these animals lacked hard skeletons. Their bodies were made entirely of soft tissues and generally rotted away when they died, leaving nothing for the fossil record. Against the odds, however, fossils have been found which seem to preserve the remains of ancient, long-extinct deuterostomes. The difficult job faced by palaeontologists is to interpret them correctly, and this is the subject of heated scientific debate. Our research project will take a new approach to analysing these controversial yet crucial fossil deuterostomes. We will study the way in which the characteristic soft-tissue features of different deuterostomes - such as muscles, tails, gill-slits and filter-feeding structures - rot and become fossilized, and determine whether we can reliably identify these characters in fossils. Fossils are essentially snapshots where decay has been frozen in time, and by decaying modern deuterostomes we will build up the kind of gory photofit - how important characters look at various stages of decay - that we need if we are to identify the characteristics of the fossils. So we will rot a variety of deuterostomes under controlled laboratory conditions. As they decompose we will carefully record the relative resistance to decay of the key features of their anatomy and how they change in appearance and position. We will also study how the soft-tissue characters of early deuterostomes actually became preserved, using a Scanning Electron Microscope to conduct detailed studies of the rare, exceptionally well-preserved fossil remains. Again, we will concentrate on important deuterostome characters, documenting their visual appearance, position and composition to determine the patterns and variability of preservation of each important feature. By analysing and comparing all these data we will be able to determine whether the fossil record can preserve recognizable early representatives of living deuterostome groups and their ancestors. Or did their remains rot too much, too fast, so that the characters that would allow them to be correctly identified were not fossilized? Nobody has ever investigated deuterostome fossils in this way (except our recent research, focussed on early vertebrates). The new project we propose builds on our expertise in this area and will allow us to develop novel methods and produce new data to address the important evolutionary questions at the heart of our proposal - the how, when and why of our own deep ancestry. Fossils have the potential to provide some answers to these big questions, but not until we learn how to correctly read the fossil record of rotted remains.