Jared Voris, a PhD student at the University of Calgary, made the miraculous discovery. The physical fossil was found by a hiker in Hays, Alberta. The Thanatos fossil has the long, deep snout characteristic of other early tyrannosaur species that roamed North America during the Cretaceous. Paleontologists attribute regional differences in skeletal morphology (skull shape) to differences in local diet. Voris explained how he arrived at the conclusion that Thanatos was an altogether new species of tyrannosaur: “Thanatotheristes can be distinguished from all other tyrannosaurs by numerous characteristics of the skull, but the most prominent are vertical ridges that run the length of the upper jaw.”

Aside from claiming the title of oldest known tyrannosaur, Thanatos is also the first new tyrannosaur discovered in fifty years. Zelenitsky explains that large carnivorous dinosaur fossils are relatively rare compared to their herbivorous cousins because of the position they occupied atop the food chain. Alberta, Canada has been a hotbed for tyrannosaur fossil discovery. Thanatos joins the ranks of Tyrannosaurus rex, Albertosaurus and Daspletosaurus, the last novel tyrannosaur discovered in Canada.