The ontogeny of the dwarf sauropod Europasaurus holgeri and the phylogeny of basal Macronaria (Saurischia, Sauropoda)

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The evolution of the sauropods, the group that contains the largest land animals of all times, is still only partly understood. Especially the basal forms of the subgroup Macronaria have been studied only exemplarily, but details of their phylogeny, character evolution, distribution, and palaeobiology are largely unknown. The wealth of new finds in recent years allows for a detailed investigation of these issues by means of two closely related approaches: 1) As a starting point, ontogenetic variations in the anatomy of the exceptionally well preserved basal macronarian Europasaurus holgeri from the Upper Jurassic of northern Germany will be studied in detail to get a better understanding of the phylogenetic significance of sauropod (especially macronarian) anatomical characters. Moreover, for the first time osteological changes related to island dwarfism can be described for dinosaurs. 2) Based on this knowledge about the anatomy of Europasaurus, the anatomy of a high number of basal macronarian taxa will be (re-)examined and coded in a newly developed character matrix, to produce a detailed phylogeny of basal Macronaria. The better understanding of phylogenetic relationships within this group will clarify the position of Europasaurus, and will make possible the development of palaeobiogeographical models of origin and distribution of this important group of sauropods. The understanding of time, tempo and ecological context of dwarfing in Europasaurus will also highly depend on these results.