Reanalysis of a dataset refutes claims of anagenesis within Tyrannosaurus-line tyrannosaurines (Theropoda, Tyrannosauridae)

Abstract

The recently described tyrannosaurine (Theropoda, Tyrannosauridae) species Daspletosaurus wilsoni was suggested to show evidence for anagenesis within the genus Daspletosaurus and derived Tyrannosaurinae. Here, we evaluate the methodology and conclusions made by the authors. Reanalysis of their dataset with additions and consistently applied methodologies, shows that there is no strong evidence for a single anagenetic lineage within ‘Tyrannosaurus-line’ tyrannosaurines throughout the latest Cretaceous. Our study demonstrates a cladogenetic Tyrannosaurinae composed of four morphologically and biogeographically distinct clades. Two of these clades are formally defined and diagnosed herein (Teratophoneini clade nov. and Tyrannosaurini). Teratophoneini is currently restricted to the southern latitudes of Campanian Laramidia, while Tyrannosaurini is present in both Campanian and Maastrichtian strata in Asia and Laramidia. Inclusion of a currently unnamed species of Daspletosaurus from the Dinosaur Park and Oldman formations to the dataset reveals that anagenesis is not found to be a driver of speciation within Daspletosaurus. We also demonstrate that all known species of Daspletosaurus do not meet previously established prerequisites for anagenesis and advise against prematurity when making conclusions concerning significant processes surrounding the mode of evolution of extinct genera with sparse and often incomplete fossil records. Future detailed anatomical description of specimens representing the proposed fourth species of Daspletosaurus will further aid in elucidating the evolution of this genus and tyrannosaurines more generally.