'Reaper of Death' Tyrannosaur That Was Close Relative of T. Rex Discovered

Researchers have discovered a large new species of tyrannosaur that lived around 80 million years ago and was closely related to the iconic Tyrannosaurus rex.

Dubbed Thanatotheristes degrootorum—the first part of which means "reaper of death"—the apex predator measured up to 30 feet in length and may have weighed as much as two tonnes when fully grown, according to a study published in the journal Cretaceous Research.

In the paper, a team of scientists from the University of Calgary and the Royal Tyrrell Museum, Canada, describe the species from fossils that were first uncovered by farmer and palaeontology enthusiast John De Groot in southern Alberta, Canada, in 2010.

According to the team, T. degrootorum is one of the oldest tyrannosaur species ever discovered in North America and is at least 2.5 million years older than its closest relative. Tyrannosaurs—meaning "tyrant lizards"—were a family of large, carnivorous dinosaurs which lived in North America, Europe and Asia near the end of the Cretaceous Period (145 to 66 million years ago.)

Tyrannosaurs tended to have massive skulls with large teeth and walked using their two long legs. The biggest animal of this group was T. rex—one of the largest predators to have ever roamed the Earth, growing up to around 40 feet in length.

"Alberta has a rich dinosaur history, and we have uncovered some of the biggest finds on Earth here in the province," study author François Therrien, from the Royal Tyrrell Museum, said in a statement. "The discovery of Thanatotheristes degrootorum is historic as it marks the first new species of tyrannosaur to be unearthed in Canada in 50 years. The last tyrannosaur described from Canada was Daspletosaurus in 1970."

When De Groot first came across the fossils, he found several skull fragments. By analyzing these bones, the paleontologists were able to identify several unique features, such as prominent vertical ridges running along the length of the upper jaw, enabling them to confirm the specimen as a new species.

"The jawbone was an absolutely stunning find. We knew it was special because you could clearly see the fossilized teeth," De Groot said in the statement.

Thanatotheristes degrootorum
Artist's illustration of Thanatotheristes degrootorum. The Royal Tyrrell Museum

The second part of the dinosaur's name pays tribute to De Groot. The first part is made up the Greek words "Thanatos"—the god of death in ancient Greek mythology—and theristes, which means one who reaps or harvests.

"We chose a name that embodies what this tyrannosaur was as the only known large apex predator of its time in Canada, the reaper of death," Darla Zelenitsky, another author of the study from the University of Calgary in Canada, told AFP.

"There are very few species of tyrannosaurids, relatively speaking," Zelenitsky said. "Because of the nature of the food chain these large apex predators were rare compared to herbivorous or plant-eating dinosaurs."

The researchers say the discovery is significant because it fills a gap in our understanding of tyrannosaur evolution.