Collaborative research: Robust estimation of biodiversity dynamics: Global versus regional patterns in the end Ordovician mass extinction of graptolites
Charles Mitchell Principal Investigator
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Intellectual Merit- Ceratopsians are among the best known of dinosaur clades due to their<br/>relative abundance, and the remarkable diversity of cranial synapomorphies such as horns<br/>and frills that diagnose more derived members of the clade. Gigantism is a trend in<br/>ceratopsian evolution that is accompanied by the evolution of progressively more<br/>complex feeding mechanisms and cranial display diversity. Heterochrony, and in<br/>particular peramorphosis have been proposed as major influences in ceratopsian<br/>evolution to explain the evolution towards large size and late ontogenetic genesis of the<br/>display in advanced forms. Likewise, the apparent hierarchical complexity of the feeding<br/>apparatus suggests an evolution of character integration through both ontogeny and<br/>phylogeny. All of these evolutionary hypotheses require detailed knowledge of both the<br/>development and phylogeny of ceratopsian dinosaurs, but so far age estimates have been<br/>poorly constrained and non-quantified and rigorous reliance on detailed phylogenies<br/>limited.<br/>In this study, an innovative approach to developmentally staging fossils based on<br/>histological sectioning and Developmental Mass extrapolation is combined with novel<br/>tree-based methods toward studying heterochrony and integration using a well-<br/>established phylogeny of Ceratopsia. Based on well-sampled growth series of seven<br/>-backbone taxa representing the diversity of the clade, and a detailed phylogeny of<br/>ceratopsians, we will examine whether there are correlated shifts in developmental timing<br/>of synapomorphies (heterochrony) relative to growth strategies, and also if blocks of<br/>characters represent integrated modules that fulfill criteria for being phylogenetically and<br/>ontogenetically constrained. These quantitative studies will allow us to evaluate previous<br/>hypotheses on the role heterochrony and integration have played in ceratopsian evolution.<br/>By providing a quantified understanding of when in ontogeny synapomorpies are<br/>expressed this research will help to resolve several taxonomic quandaries related to the<br/>validity of species based on juvenile holotypes and provide a more accurate<br/>understanding of ceratopsian diversity.<br/>Broader Impact: This research represents a new integrative exploration of evolutionary<br/>processes in a well-known group of dinosaurs. The novel methods and the results of this<br/>research promise to be widely applicable to fields as diverse as population biology,<br/>developmental biology, macroevolution and evo-devo, and will be disseminated through<br/>peer -reviewed journals, presentations at professional meetings and professional web-<br/>sites. Two graduate and two undergraduate students will be trained through this project,<br/>and aspects of the research will be incorporated into university courses taught by both<br/>PIs. Both PIs are involved with developing exhibits for natural history museum, and<br/>parts of this research will be incorporated into two ongoing exhibit projects, and<br/>associated educational web-sites and programming. Given the media interest in dinosaur<br/>research, many opportunities to disseminate results of this work to the public will no<br/>doubt arise.