Anagenesis and the tyrant pedigree: A response to “Re-analysis of a dataset refutes claims of anagenesis within Tyrannosaurus-line tyrannosaurines (Theropoda, Tyrannosauridae)”

Abstract

Taxonomic diversity in the derived tyrannosaurine Daspletosaurus has been hypothesized to represent a variety of evolutionary patterns by different authors. The recent description of D. wilsoni, the third species of this genus, was proposed to support the paraphyly of Daspletosaurus and participation of its species within a single anagenetic lineage terminating at the base of a clade formed by Tyrannosaurus and other gigantic tyrannosaurines (Tarbosaurus, Zhuchengtyrannus). However, a recent reanalysis including additional data has challenged this interpretation, instead recovering Daspletosaurus as a monophyletic sister group to Tyrannosaurus and its closest relatives, characterized by several cladogenetic events. Here we show that incorporating further data and correcting erroneous interpretations of relevant anatomical features overturns this result. Using a novel phylogenetic analysis including additional specimens, we recover a paraphyletic Daspletosaurus, with species of this genus forming successive sister taxa to Tyrannosaurus-line tyrannosaurines. This result facilitates an interpretation of currently recognized Daspletosaurus species as representing a single anagenetic lineage, in agreement with the stratigraphic distribution of relevant specimens and a qualitative analysis of the range of morphological variation observable within D. wilsoni.