Reconstructing the evolutionary relationships of Daspletosaurus has been hampered by the rarity of good specimens, and many researchers disagree as to whether these tyrannosaurids represent a single lineage evolving in place, or several closely related species that do not descend from one another.

In research published today in PeerJ, Elías Warshaw and Denver Fowler report the discovery of a new species of Daspletosaurus from Montana: Daspletosaurus wilsoni, found in rocks intermediate in age between other tyrannosaurs found in the region.

The new species displays a mix of features found in more primitive tyrannosaurs from older rocks, like a prominent set of horns around the eye, as well as features otherwise known from later members of this group (including T. rex), like a tall eye socket and expanded air-pockets in the skull. In this way, D. wilsoni is a "half way point" or "missing link" between older and younger tyrannosaur species.

These findings suggest that previous research was correct in identifying several species of Daspletosaurus as a single evolving lineage, and supports the descent of T. rex from this group.