Dickinson paleontologist co-authors report on new tyrannosaur species
Nov. 30—DICKINSON — In a recently published paper, Montana State University Researcher Elías Warshaw and Badlands Dinosaur Museum Curator
Denver Fowler
reported the discovery of a new species of Daspletosaurus from Montana: Daspletosaurus wilsoni.
Tyrannosaurids, the family of dinosaurs that includes T. rex, have been known from North America and Asia for over a century, yet many details of their evolutionary history remain unclear. Debates regarding Daspletosaurus have been going on since the 90s. This is the large tyrannosaurid that was known to roam Montana and Alberta.
It has been proposed to be an ancestor of T. rex itself. Reconstructing the evolutionary relationships of Daspletosaurus has been hampered by the rarity of good specimens. 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.
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. Warshaw and Fowler describe D. wilsoni as a "halfway 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.
In North America's Late Cretaceous Period, many dinosaur families are represented by multiple closely-related species. These were previously thought to represent diversity, ie. that they lived at the same time, which would be evidence of branching evolution. However, a wealth of new specimens and a better understanding of their placement in time has changed the game. It has become clear that many of these species are distinctly separated in time, forming consecutive ladder-like steps in a single evolutionary lineage where one ancestral species evolves directly into a descendant species.
This is called the anagenesis mode of evolution, as opposed to cladogenesis, in which successive branching events produce many species that are closely related and therefore look similar to each other, but represent evolutionary "cousins" rather than ancestors and descendants.
"Indeed, as anagenesis continues to be identified among fossil lineages, the predominant relative frequency of strictly cladogenetic evolutionary models (e.g., punctuated equilibria; Eldredge & Gould, 1972) must eventually come under scrutiny," the authors
state
in their paper. "Future explorations of evolutionary mode in fossil taxa, including further tests of the hypotheses presented here,will be important in this regard, and have the potential to refine understanding of the pattern and process of dinosaur evolution."
They said their findings support the addition of tyrannosaurs to a growing list of dinosaurs, including horned and duck-billed dinosaurs, for which anagenesis (linear evolution) has been proposed. This seems to suggest that linear evolution is more widespread in dinosaurs, with branching evolution being less frequent than previously thought. Warshaw is continuing with further research to learn more about the link between T. rex and Daspletosaurus.
The new species is based on a skull and partial skeleton recovered by the Badlands Dinosaur crew from 2017 to 2021. The original discovery was made in 2017 by crewmember John (Jack) Wilson who spotted a small flat piece of bone projecting out from the bottom of a towering cliff. This distinctive flat bone was the middle part of the nostril of a tyrannosaur. Careful digging around the bone revealed a complete premaxilla — the bone at the tip of the snout. As one might have guessed, Daspletosaurus wilsoni is named after Wilson and means "Wilson's frightful reptile."
A few broken vertebrae from around the site showed that this was a large tyrannosaur, but there was 25 feet of rock overlying the bones. Field crews in 2020 and 2021 used a jackhammer to dig down to the bone layer whereupon we discovered a partial skull and skeleton. The seemingly endless task of removing overburden gave rise to the specimen's nickname "Sisyphus," after the figure from Greek mythology.
The Badlands dinosaur crew had a bumper year in 2017, as Fowler and Wilson
found
four tyrannosaur sites in the area. These have been successively excavated over the past five years, revealing three partial skeletons and what appears to be a mostly complete articulated skeleton.
The dinosaur museum is accepting
volunteers
to assist with lab work and collections maintenance duties. Volunteers must be 15 or older and preferably able to work shifts of two hours or more. To learn more call 701-456-6225 or email Denver.fowler@dickinsongov.com.
The Dickinson Museum Center is open Monday through Saturday from 9 a.m. to 5 p.m. It will host a Christmas celebration on Friday, Dec. 2 from 3 to 6 p.m. with live music and free admission.
