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Phylogeny of Allosauroidea (Dinosauria: Theropoda): comparative analysis and resolution
Allosauroidea, a clade of large-bodied theropod dinosaurs that ranged from the Middle Jurassic until the Late Cretaceous, has been the subject of extensive phylogenetic study. However, despite the publication of 12 cladistic analyses little phylogenetic consensus has emerged, frustrating attempts to use these dinosaurs to study character evolution, biogeography and the quality of the fossil record. Here we analyse a core subset of allosauroids using cladistic methodology and several comparative methods. After reviewing previous studies and their points of disagreement, we present a new cladistic analysis that integrates data from these studies with new characters. This analysis finds strong support for placing Sinraptor as a basal allosauroid, Neovenator as a basal member of Carcharodontosauridae and Acrocanthosaurus as amore derived member of Carcharodontosauridae, rather than the sister taxon of Allosaurus as sometimes advocated. The current dataset is compared in detail to those of previous studies to determine the degree of overlap and the basis for differing topologies. These comparisons show that scoring differences, character choice and taxonomic sampling all play a major role in generating incongruence. Finally, the recovered most parsimonious topology is used to assess character evolution, stratigraphical congruence and biogeography. This topology shows a strong overall match with the stratigraphical record and is much more congruent with stratigraphy than any alternative topology. The biogeographical history of core allosauroids is found to be congruent with the breakup sequence of Pangaea, but more complete assessment is hampered by sampling biases.
Stratigraphically calibrated phylogeny of Allosauroidea, based on the results of the current analysis. Thick lines indicate major ghost lineages, while thin lines reflect error in the temporal resolution of taxon occurrences (not true time ranges). Absolute dates for point occurrences are taken as the midpoint of the stage (or stages, depending on stratigraphical resolution) in which the taxon first appeared. All absolute dates based on the time scale of Gradstein et al. (2004).