Thanatotheristes degrootorum is a tyrannosaurid that lived 80 million years ago

Thanatotheristes degrootorum fossil bonesAn article published in the journal “Cretaceous Research” reports the identification of a new species of tyrannosaurid that lived in today’s Canada about 80 million years ago, in the Cretaceous period. A team of researchers named it Thanatotheristes degrootorum after examining a partial skull with the bones of the upper and lower jaws, discovered in 2010 near the city of Hays. The characteristics of the available fossils convinced the researchers that it was a tyrannosaurid of a different species from the ones already known, the oldest discovered in Canada, useful to understand the evolution of the family to which the iconic T. rex belongs.

The tyrannosaurid (Tyrannosauridae) family, carnivorous theropod dinosaurs, is made up of large predators that lived in the Cretaceous period. Tyrannosaurus rex is by far the most famous but over the past few decades various species have been discovered that are adding a lot of information on their evolution and diversification. Often the fossils studied are partial skeletons and this makes it difficult to establish the various relationships with certainty, also leading to discussions among paleontologists and to different proposals from their family tree.

Jared Voris, a PhD student at the Canadian University of Calgary, examined the fragmentary fossils attributed to the new species after seeing them at the Royal Tyrrel Museum, where they were placed in a drawer after they were found. Fossil hunters John and Sandra De Groot discovered them in 2010 near the Canadian city of Hays and now the new species bears their name.

The top image (courtesy Jared Voris. All rights reserved) shows the jaw bones found and a drawing of their complete shape. The bottom image (courtesy of the Royal Tyrrell Museum. All rights reserved) shows an artistic reconstruction of Thanatotheristes degrootorum’s head.

Thanatotheristes degrootorum shows similarities with the genus Daspletosaurus, created in 1970 for the species Daspletosaurus torosus, to which the species Daspletosaurus horneli was added after its identification was reported in an article published in March 2017 in the journal “Scientific Reports”. The differences were still considered enough by the researchers to create a new taxonomic genus but they also created a new group that includes both genres that they called Daspletosaurini.

These recent discoveries show anatomical differences in the various groups of tyrannosaurids which may be due to adaptations to different environments, with different prey and different hunting strategies. Thanatotheristes degrootorum had a long snout, similar to that of the primitive tyrannosaurs that lived in the south of today’s USA. Other species that evolved in a more southerly area had a shorter bulldog-like snout.

The availability of few bones makes the extrapolations of other characteristics of Thanatotheristes degrootorum approximate. Based on information about other tyrannosaurids, the researchers estimated that this dinosaur was around 8 meters long and probably hunted large herbivores such as Xenoceratops and Colepiochephale, which were present in its ecosystem.

Jared Voris intends to explore other areas of the rock formation where Thanatotheristes degrootorum’s fossil bones were found hoping to discover other specimens. Discovering more bones could provide new information on the differences between the various species, important to understand the evolution of tyrannosaurids and how these large carnivorous dinosaurs’ hunting strategies.

Artist's reconstruction of Thanatotheristes degrootorum's head

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