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A newly described 8-meter-long (26-foot) tyrannosaur nicknamed the “reaper of death” represents not only the oldest known tyrannosauroid from Canada, but also a new genus and species related to the notorious Tyrannosaurus rex.
The 79-million-year-old fossils of Thanatotheristes degrootorum were discovered in 2010 along the banks of the Bow River in Alberta, Canada. Outfitted with a long snout and unique ridges along the upper jaw, its unique physical features were likely adaptations to different environments, plant-eating prey, and hunting strategies that reduced competition and gave the animal a better chance at survival. The fragmentary fossils, which included parts of the skull as well as the upper and lower jawbones, is the oldest known tyrannosaur discovered in northern North America and the first to be identified in Canada in the last 50 years.
“This is the oldest occurrence of a large tyrannosaur in Canada, found in an older window of time than where previous tyrannosaurs have been found,” said study co-author Dr Darla Zelenitsky, University of Calgary principal dinosaur researcher and assistant professor in the Faculty of Science’s Department of Geoscience, in a statement.
Tyrannosaurs dominated landscapes throughout Laurasia, an ancient continental mass that once included North America and Europe during the Late Cretaceous period between 66 and 145 million years ago. Over time, the group of two-footed predatory dinosaurs likely diversified, evolving distinct skull shapes, body sizes, and other physical features as they spread into different environments.
To better understand the differences between species found in northern and southern North America, researchers took 3D surface scans and measurements of the cranial bones and compared the anatomy of T. degrootorum with published descriptions of other tyrannosaurids. Their unique morphology links them to two other species, and together they form a new clade of dinosaurs called Daspletosaurini, helping to inform understanding of dinosaur evolution during the Late Cretaceous, write the study authors in Cretaceous Research.
“With this new species, we now know that tyrannosaurs were present in Alberta prior to 77 million years ago, the age of the next-oldest tyrannosaur,” said study co-author Dr François Therrien, curator of dinosaur palaeoecology at the Royal Tyrrell Museum. “We can tell from the skull how Thanatotheristes is related to the other, better-known tyrannosaurs from Alberta.”
The researchers hope to continue comparing tyrannosaur species from different geological regions to tell us more about the evolution of these unique beasts.
