Meet Thanatotheristes degrootorum: T. Rex's Older Cousin "The Reaper of Death"

Tuesday, February 11, 2020

Thanatotheristes degrootorum. Image credit: Julius Scotonyi, Royal Tyrrell Museum.

A new species of tyrannosaurine dinosaur that lived about 79.5 million years ago (Cretaceous period) has been identified from fossils found in Alberta, Canada.

“We are thrilled to announce the first new species of tyrannosaur to be discovered in Canada in 50 years,” said Dr. François Therrien, curator of dinosaur paleoecology at the Royal Tyrrell Museum.

“The last tyrannosaur described from Canada was Daspletosaurus in 1970.”

The newly-identified species was approximately 8 m long (26.2 feet) and likely preyed on large plant-eating dinosaurs, such as the horned Xenoceratops and the dome-headed Colepiochephale.

Dubbed Thanatotheristes degrootorum, the ancient creature is the oldest tyrannosaur known from Canada and northern North America.

Researchers said Thanatotheristes degrootorum was around eight metres long and hunted around 80 million years ago

“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 Dr. Darla Zelenitsky, a dinosaur researcher at the University of Calgary.

“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,” Dr. Therrien added.

“We can tell from the skull how Thanatotheristes degrootorum is related to the other, better-known tyrannosaurs from Alberta.”

The jaw bones of Thanatotheristes degrootorum. Image credit: Jared Voris.

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.

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

“John always said that one day he would find a dinosaur skull. Finding the jaw was exciting. Hearing that it is a new species, and seeing it given our family name, was beyond belief,” added Sandra De Groot.

The paleontologists found features of Thanatotheristes degrootorum’s skull that had not been seen before in other tyrannosaurs.

The fossil has several physical features, including ridges along the upper jaw, which clearly distinguishes it as being from a new species.

The diagnostic evidence showed that Thanatotheristes degrootorum is a close relative of two other well-known tyrannosaur species, Daspletosaurus torosus and Daspletosaurus horneri. All three species form a newly named group of dinosaurs called Daspletosaurini.

“This group had longer, deeper snouts and more teeth in the upper jaws than tyrannosaurs found in the southern U.S., which had shorter, bulldog-like faces,” said Jared Voris, a Ph.D. student at the University of Calgary.

“This discovery is significant because it fills in a gap in our understanding of tyrannosaur evolution,” Dr. Therrien said.

Thanatotheristes degrootorum provides scientists with insights into the tyrannosaur family tree, and shows that tyrannosaurs from the Cretaceous of Alberta were more diverse than previously known.”

The discovery is reported in a paper in the journal Cretaceous Research.


Jared T. Voris et al. A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids. Cretaceous Research, published online January 23, 2020; doi: 10.1016/j.cretres.2020.104388