The evolution, palaeoecology and biogeography of titanosaurian dinosaurs

Overview Titanosaurs were a group of sauropod dinosaurs (gigantic, long-necked herbivores) comprising at least 50 genera. Jurassic titanosaurs were rare, but in the Cretaceous they became diverse, abundant and geographically widespread. Titanosaurs represent a major component of many Cretaceous terrestrial ecosystems and have therefore played an important role in hypotheses relating to the diversity and biogeography of the late Mesozoic. For example: i. Biogeography - Titanosaurs are known from all continents (except Antarctica) and have played a prominent role in hypotheses linking organismal distribution during the Cretaceous to Pangaean fragmentation and sea level. For example, it has been proposed that marine regression and tectonic activity in the Late Cretaceous formed landbridges that enabled South American titanosaurs to invade North America and African titanosaurs to invade Europe. ii. Diversity - The Cretaceous diversification of titanosaurs, apparently at the expense of other groups, has generated several competing explanatory hypotheses, including: (i) adaptations, such as body armour, gave titanosaurs a competitive advantage; (ii) other groups went into decline because of environmental change, enabling titanosaurs to diversify via invasion of vacant niches; and (iii) the relative success of titanosaurs is an artefact created by a biased fossil record. Unfortunately, the taxonomy and evolutionary relationships of titanosaurs are poorly understood compared to other dinosaurs. Only one previous study has attempted a detailed reconstruction of their evolutionary relationships, and this failed to produce clear results because of methodological flaws. The lack of a well-supported taxonomic and phylogenetic framework for titanosaurs severely hampers attempts to test the numerous hypotheses that explain the evolutionary history of the group. The Project The Natural History Museum, London, has collections of titanosaur material from the UK, India, South America and Romania. In particular, it has important remains of the Late Cretaceous titanosaur Magyarosaurus. These specimens have received little if any attention since their collection in the late 19th and early 20th centuries. A detaled re-evaluation of this material promises to reveal important new information on the anatomy and relationships of titanosaurs and should enhance the scientific value of the Natural History Museum's dinosaur collection. Aside from the currently untapped potential of the London specimens, there has also been a great influx of new data during the past decade (e.g. the number of titanosaur genera has increased by approximately 50% in this period). A project that examines titanosaur taxonomy and phylogeny is thus overdue and has the potential to modify or overturn several palaeoecological and biogeographic hypotheses. This project has two main aims. First, the student will collect information on the anatomy and geographic/stratigraphic distributions of titanosaurs, revise the taxonomy of several problematic forms, and build a detailed evolutionary tree using the most up-to-date phylogenetic methods. This work will provide the essential foundations required to achieve the second aim - the testing of biogeographic and evolutionary hypotheses using distributional data and the evolutionary tree. For example, comparisons of diversity curves for titanosaur and non-titanosaur sauropod groups can test the hypothesis that the former drove the latter to extinction through competitive displacement. Similarly, application of biogeographic methods (such as TREEFITTER and PACT) will enable statistical tests of hypotheses that claim that titanosaur evolution has been constrained by geographic events (e.g. Pangaean break-up). The results of this project should have a significant impact on our understanding of titanosaur evolution, and will also have wider implications for studies of Mesozoic terrestrial ecosystems and extinctions.