Thanatotheristes is a genus of tyrannosaurid dinosaur from the Late Cretaceous of Laramidia, approximately 80.1-79.5 Ma. Thanatotheristes contains only one species, T. degrootorum. By early 2018, the University of Calgary master’s student had spent more than a year poring over bones in museum collections, studying how tyrannosaurs matured from hatchlings into hulking terrors. During one visit to the collections of Alberta’s Royal Tyrrell Museum of Palaeontology, he noticed a cabinet with fossils he couldn’t quite place. Now, after two years of careful research, Voris and his colleagues have identified the first new Canadian tyrannosaurid to be found in 50 years. Stretching 26 feet in length, the dinosaur is named Thanatotheristes, Greek for “reaper of death.” Aged roughly 79.5 million years, Thanatotheristes degrootorum sits near the base of the tyrannosaurs’ ascent to ecological domination. The unearthed skull fragments—including upper and lower jawbones, teeth, and a partial cheekbone—sketch out the early pages of how tyrannosaurids, the tyrannosaur subgroup that includes T. Rex, rose to power and became top predators.“I tried to be really meticulous with identifying features that made it unique,” says Voris, who is now a Ph.D. student at the University of Calgary. “It’s interesting to have the opportunity to name a new species—and I’m hoping it isn’t all downhill from here.” A partial skull and the upper and lower jaw bones of the new tyrannosaur were found by farmers and paleontology enthusiasts John and Sandra De Groot in 2010 near the town of Hays. Alberta is a tyrannosaur graveyard. There rest great carnivores of the Cretaceous, such as Albertosaurus, Gorgosaurus, Daspletosaurus and, of course, Tyrannosaurus Rex. Now, paleontologists in the province have announced the discovery of Canada’s oldest known tyrannosaur: Thanatotheristes degrootorum, or “the Reaper of Death.”With its razor-sharp teeth and formidable two-ton frame, the newly discovered species terrorized the region some 79.5 million years ago. Though smaller than T. rex, it still measured about 30 feet long and about 8 feet tall. The new species was at least 2.5 million years older than its closest relatives, which may provide insight into when tyrannosaurs grew from small carnivores into the apex predators that perished 66 million years ago.“Prior to the discovery, we knew all the most famous tyrannosaurs like T. rex, Albertosaurus, Gorgosaurus, were all coming from the last 10 or so million years of the Cretaceous,” said François Therrien, a paleontologist at the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta, and an author on the paper. “Now, with the new species we’ve actually pushed back the record of tyrannosaurs.” Thanatotheristes contains only one species, T. degrootorum. Fossils of this taxon are found in the Foremost Formation of Alberta, Canada, coexisting with medium-sized ceratopsids like Xenoceratops Foremostensis and small pachycephalosaurids.

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