A new species of North American, Late Cretaceous tyrannosaur has been announced. It is the third species in the Daspletosaurus genus. Daspletosaurus wilsoni is older than D. horneri, but geologically younger than D. torosus. The skull demonstrates a mix of traits found in primitive tyrannosaurs as well as several more derived characteristics associated with later members of the Tyrannosauridae such as Tyrannosaurus rex.
Writing in the on-line, open access journal PeerJ, the researchers from the Badlands Dinosaur Museum (North Dakota), suggest that the discovery of a tyrannosaur intermediate in age between the previously described species of this genus, supports earlier research identifying several species of Daspletosaurus as a single evolving lineage, and supports the descent of T. rex from this group.
From the Judith River Formation (Campanian Faunal Stage)
The fossil specimen was discovered in 2017. It consists of a partial, disarticulated skull and jaw bones with an exceptional degree of preservation along with vertebrae, a rib and the first metatarsal. The material comes from Judith River Formation exposures in north-eastern Montana. The fossil was found by John Wilson and the species name has been erected in his honour.
The new species displays a mix of characteristics found in more primitive, geologically older tyrannosaurs. For example, D. wilsoni sports 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, this newly described species represents a transitional form between older and younger tyrannosaur species.
Several tyrannosaurs have now been named from the Upper Cretaceous of North America. The researchers note that many of the species are very closely related, forming consecutive sequences where one species evolves into another species over time. When one ancestral species evolves into a second descendant species, this is referred to as anagenesis, as opposed to cladogenesis when successive branching events produce many species that are closely related to each other but not direct descendants of a single species.
The authors of the scientific paper conclude that anagenesis might be the driver of evolutionary change within the Dinosauria at the end of the Cretaceous rather than cladogenetic evolutionary models.
The first species of Daspletosaurus (D. torosus) was named and described in 1970, the second species, the geologically youngest species, D. horneri was named in 2017. Few models of this tyrannosaur existed but in 2013 CollectA added a Daspletosaurus model to their Prehistoric Life model range. More recently (2021), Safari Ltd introduced a Daspletosaurus figure into their Wild Safari Prehistoric World range.
To view the Wild Safari Prehistoric World range of models available from Everything Dinosaur: Safari Ltd Dinosaur and Prehistoric Animal Models.
The scientific paper: “A transitional species of Daspletosaurus Russell, 1970 from the Judith River Formation of eastern Montana” by Elias A. Warshaw and Denver W. Fowler published in PeerJ.