A transitional species of Russell, 1970 from the Judith River Formation of eastern Montana.

Here we describe a new derived tyrannosaurine, sp. nov., from Judithian strata (~76.5 Ma) intermediate in age between either of the previously described species of this genus. displays a unique combination of ancestral and derived characteristics, including a cornual process of the lacrimal reduced in height relative to and more basal tyrannosaurines, and a prefrontal with a long axis oriented more rostrally than in and more derived tyrannosaurines. The description of this taxon provides insight into evolutionary mode in Tyrannosaurinae, lending strength to previous hypotheses of anagenesis within and increasing the resolution with which the evolution of this lineage can be reconstructed. Cladistic phylogenetic methods, stratigraphy, and qualitative analysis of the morphology of relevant taxa supports an anagenetic model for the origin of morphological novelty in this genus, highlighting the predominance of anagenetic evolution among contemporary dinosaur lineages.