A new T. rex relative called the ‘reaper of death’ has been discovered in Canada

An illustration of Thanatotheristes degrootorum.

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An illustration of Thanatotheristes degrootorum.
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Julius Csotonyi

The oldest known member of the tyrannosaur family stalked the plains of southern Alberta about 80 million years ago.

That’s the finding of a new study identifying the previously unknown dinosaur. Though the fossils were discovered a decade ago, paleontologists confirmed that it was a new species – and gave it a name – only this week.

The first part of that name, Thanatotheristes degrootorum, means “reaper of death” in Greek.

According to the study, published in the journal Cretaceous Research, the creature was 8 feet tall and the length of a school bus. It weighed 2 tons and sported 2.7-inch-long serrated teeth set into a skull adorned with pronounced ridges along its snout.

“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, a paleoecologist and coauthor of the new study, told AFP.

“The nickname has come to be Thanatos,” she added – the Greek word for “god of death.”

Thanatos is not only the oldest known dinosaur of its kind in North America but also the first tyrannosaur species discovered in Canada since 1970.

The oldest Tyrannosaur on the North American continent

An artist's impression of Thanatotheristes.

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An artist’s impression of Thanatotheristes.
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Julius Csotonyi/University of Calgary

Zelenitsky and her team determined that the Thanatos fossils were 79.5 million years old, making the creature the oldest known tyrannosaur species ever discovered in the US or Canada.

Tyrannosaurs were a type of carnivorous bipedal dinosaur called therapods.

The “reaper of death” lived about 10 million years before the Tyrannosaurus rex, which lived at the tail end of the Cretaceous period 66 million years ago.

It’s also smaller than the T. rex, which could reach lengths of 40 feet and weigh up to 9 tons as a full-grown adult.

A full-grown Tyrannosaurus rex weighed between 6 and 9 tons and was up to 43 feet long.

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A full-grown Tyrannosaurus rex weighed between 6 and 9 tons and was up to 43 feet long.
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Illustration by Zhao Chuang/courtesy of PNSO

Paleontologists have found three other tyrannosaurs in Alberta over the years: Albertosaurus, Daspletosaurus, and Gorgosaurus. Like the T. rex, these three roamed later than Thanatos, between 77 million and 66 million years ago.

‘Scarface’ skull helped paleontologists identify Thanatos

The Thanatos remains discovered in Alberta consist of partial skulls and jaw bones with embedded teeth. They were first uncovered in 2010 by John and Sandra de Groot.

Lead study author Jared Voris holds up a fragment of a Thanatos jaw.

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Lead study author Jared Voris holds up a fragment of a Thanatos jaw.
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Jared Voris

The study authors were able to determine that Thanatos was a new species – distinct from all other tyrannosaurs found in Alberta – by analyzing parts of its skull. The proof beyond doubt, according to lead study author Jared Voris, was a pair of vertical ridges that run the length of Thanatos’ upper jaw.

The researchers also found a 4-inch-long scar on the predator’s right upper jawbone. That’s a clue that the “reaper” might have fought with other dinosaurs.

“It’s a Scarface,” Scott Persons, a paleontologist who isn’t affiliated with the new study, told National Geographic.

An illustration of Thanatos skull fragments superimposed on a full skull.

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An illustration of Thanatos skull fragments superimposed on a full skull.
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Jared Voris

3 Tyrannosaur body types

The study authors said Thanatos’ discovery provides further evidence that different clades, or groups, of tyrannosaurs lived and thrived in separate areas of North America between 80 million and 74 million years ago.

The new finding also gives paleontologists new insights into how the T. rex’s older relatives differed in size and body shape from their successors.

Amateur paleontologist John de Groot holds up a cast of the Thanatos jawbone that he found with his wife, Sandra, in 2010.

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Amateur paleontologist John de Groot holds up a cast of the Thanatos jawbone that he found with his wife, Sandra, in 2010.
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John DeGroot

Each group of these dinosaurs had its own “morphotype,” or body plan, the researchers said.

Thanatos belongs to a group of hefty tyrannosaurs that had long deep-snouted faces and lived in southern Alberta and Montana. The Albertosaurus, meanwhile, was a svelter long-legged tyrannosaur that lived farther north in Canada. The third group, which had stouter, shorter snouts, lived in the southern US.

One possible reason for this variation in tyrannosaur body types is that each clade likely hunted different types of prey.

Pieces of Thanatos' upper and lower jawbones.

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Pieces of Thanatos’ upper and lower jawbones.
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Jared Voris

“Tyrannosaurs had a dynamic evolutionary history,” Steve Brusatte, a paleontologist who wasn’t involved in the study, told National Geographic. He added, “They weren’t all monstrous superpredators like T. rex, but there were many little subgroups that had their own domains and their own distinctive body types.”