SHAKING THE TREES: FURTHER ANALYSIS OF THE MANIRAPTORIAN EVOLUTIONARY FRAMEWORK IN REGARDS TO THE “ALLIED PLUNDERER”, DAKOTARAPTOR STEINI (THEROPODA: DROMAEOSAURIDAE)

The Hell Creek Formation (Maastrichtian; 66 ma) preserves a detailed record of the last 1.3 million years of life in Laramidia before the Cretaceous-Paleogene extinction. Understanding the ecological diversity during this critical window of geologic time is essential to resolving the effects of the K/Pg extinction in this region, as well as the origins of its inhabitants. As such, close examination of the Hell Creek fauna has become an important focus for researchers. One recent update to the Hell Creek fauna, is, Dakotaraptor steini a large maniraptoran. Dakotaraptor, with a reconstructed length of 5.5m, is among the largest of any known maniraptoran, and thereby revises our understanding of the paleoecology and biodiversity of the Hell Creek biota. Contrary to other giant maniraptorians such as Achillobator and Utahraptor; D. steini possesses morphology that would have been well suited for an agile lifestyle. The two synergic characteristics of a large body size and sleek body plan make Dakotaraptor a deadly addition to the Hell Creek biota. Dakotaraptor’s phylogenetic affinities, may have further implications for the origins of the taxon. Herein we present a more thorough and inclusive analysis based on multiple phylogenetic analyses. Using phylogenetic modeling software and several data matrices from recent literature, we demonstrate a clear separation between Dakotaraptor and its coeval maniraptoran form, Acheroraptor, and resolve Dakotaraptor’s position within the maniraptora. Retesting the alpha branches of the trees support these preliminary findings. We ran three different matrices of at least 116 unordered and unweighted characters with supporting methods, resulting in consistent resolution. This more robust phylogeny reinforces the increased known diversity of maniraptorans in the formation, and provides an evolutionary framework for their origin and their extinction at the end of the Maastrichtian.