A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids

Upper Cretaceous tyrannosauroid material from North America was primarily known from upper Campanian through Maastrichtian formations until the recent discovery of derived tyrannosaurid taxa from lower-to-mid Campanian deposits in the southwestern United States. However, diagnostic material from contemporaneous deposits further north in Alberta (Canada) and Montana (USA) has yet to be documented. Here we report the discovery of a new tyrannosaurine tyrannosaurid from the mid-Campanian Foremost Formation of Alberta, Thanatotheristes degrootorum gen. et. sp. nov, which helps fill this gap. The new tyrannosaurine, diagnosed by five autapomorphies, is found to be the sister taxon to the late Campanian genus Daspletosaurus. Thanatotheristes is distinct from Daspletosaurus based on several features, and lacks at least two apomorphies of the latter taxon. Together, these taxa form the newly established Daspletosaurini, a clade of long-, deep-snouted tyrannosaurines endemic to northern Laramidia during the Campanian. Our study demonstrates that Tyrannosauridae is composed of several geographically-segregated clades rather than a series of monogeneric successive sister taxa as recovered by previous studies. The geographic segregation of tyrannosaurid clades within North America provides renewed evidence for provinciality among large theropods during the Late Cretaceous.