New Information on the Cranial Anatomy of Acrocanthosaurus atokensis and Its Implications for the Phylogeny of Allosauroidea (Dinosauria: Theropoda)

摘要: Background Allosauroidea has a contentious taxonomic and systematic history. Within this group of theropod dinosaurs, considerable debate surrounded the phylogenetic position large-bodied allosauroid Acrocanthosaurus atokensis from Lower Cretaceous Antlers Formation North America. Several prior analyses recover as sister taxon to smaller-bodied Allosaurus fragilis known America Europe, others nest within Carcharodontosauridae, allosauroids that attained cosmopolitan distribution during Early Cretaceous. Methodology/Principal Findings Re-evaluation well-preserved skull (NCSM 14345) provides new information regarding palatal complex inner surfaces mandible. Previously inaccessible internal views articular nearly every element are described. Twenty-four morphological characters identified variable in Allosauroidea, combined with 153 previously published characters, evaluated for eighteen terminal taxa. Systematic analysis dataset recovers single most parsimonious topology placing member agreement several recent well Carcharodontosauridae. Conclusions/Significance A revised diagnosis finds species is distinguished by four primary including: presence knob on lateral surangular shelf; enlarged posterior foramen; supraoccipital protruding double-boss nuchal crest; pneumatic recess medial surface quadrate. Furthermore, recovered phylogeny more closely agrees stratigraphic record than hypotheses place related fragilis. Fitch optimization body size also consistent placement clade larger carcharodontosaurid taxa near base Allosauroidea. This supports previous global radiation Cretaceous.