The origin of animal phyla was one of the most significant events in the evolutionary history of life, but the mechanism by which this occurred is unclear. Attempts to address this issue have created research links between otherwise disparate disciplines, from developmental biology to palaeontology, and from comparative anatomy to molecular phylogenetics. Because of the apparently sudden appearance of animal phyla in the fossil record, most explanations for the emergence of animals are macroevolutionary, invoking processes that are not apparent today. The alternative is that phyla evolved by the gradual accumulation of small-scale changes, i.e. microevolution. Such gradualistic models require evidence for the step-wise assembly of phylum-level body plans, but there is precious little record of this. This may be because a mineralized skeleton was a relatively late innovation in most phyla and thus their earliest representatives are unlikely to be preserved as fossils. Not so the echinoderms, which have an outstanding fossil record because a mineralized skeleton was among their first derived characters; consequently, there is a rich record from which the assembly of their body plan may be deciphered. The principal aim of the proposed research is to uncover the evolutionary assembly of the echinoderm body plan as an exemplar for understanding the mode of assembly of phylum-level body plans more generally. Indeed, there are reasons beyond their excellent fossil record for focusing on echinoderms as a model system – echinoderms have been a focus of investigation in developmental embryology classically and this remains true today. The central objectives of this project are:
• To elucidate the anatomy of basal fossil echinoderms, thereby resolving their phylogeny and uncovering the sequence in which the defining characteristics of living echinoderms were acquired.
• To test the principal theory of skeletal homologies in echinoderms.
These objectives will be met by marshalling state-of-the-art methods, including X-ray microtomography, scanning electron microscopy and whole-mount in situ hybridization. The proposed programme of research will produce results that have wide ranging implications for understanding animal evolutionary history.
The origin of animals was one of the most significant events in the evolutionary history of life, but the mechanism by which this occurred is unclear. Debate centres on whether this event was the result of numerous small evolutionary changes or relatively few large-scale ones. In theory we can study the fossilized remains of animals to discriminate between these possibilities, but unfortunately the early fossil records of most groups are apparently quite incomplete. The echinoderms (sea urchins, starfish and the like) are an exception to this because they possess a hard, mineralized skeleton and, hence, even their earliest representatives are preserved as fossils. However, to accurately interpret this rich record we also need to understand the anatomy, development and genetics of living animals. The principal aim of the proposed research is to reconstruct the origin and early evolution of echinoderms; this will provide important insights into the emergence of animals more generally. I will achieve this goal by: (1) reconstructing the early evolution of echinoderms and (2) testing the major existing theory for homologies (structures with a shared ancestry) in echinoderms. This research will involve a synthesis of palaeontological, developmental and molecular techniques, which is the most effective means of deciphering animal evolution. Selected fossil echinoderms will be studied using high-resolution micro-CT scanning and computer software to generate 3-D 'virtual fossils'. In combination with images obtained from scanning electron microscopy, this approach will allow previously hidden details of fossils to be studied and illustrated, providing new data on the relationships and mode of life of these extinct animals. The development of living echinoderms from embryo to adult will be studied using high-powered microscopes and a molecular technique for analyzing the expression patterns of genes. In this manner it will be established if the model for determining fundamental homologies in echinoderms is accurate. This project is important as it will help us uncover the morphology and relationships of extinct ancestral animals, and the novelties that arose during their evolution into modern forms. It may also help to infer the pattern and process of deep, fundamental events in animal evolutionary history. Ultimately, this research aims to demonstrate that only by integrating all relevant avenues of enquiry and lines of evidence can we achieve an optimal understanding of organismal evolution.