A new large tyrannosaur from Alberta, a predatory dinosaur whose name means “reaper of death,” was found by palaeontologists from the University of Calgary and the Royal Tyrrell Museum.
The 79-million-year-old fossil, named Thanatotheristes, is the oldest tyrannosaur reported from northern North America and the first new tyrannosaur species found in Canada in 50 years, according to the research team’s report.
“It’s the oldest example of a large tyrannosaur in Canada found in an older window of time than in previous tyrannosaurs,” says Dr Darla Zelenitsky, a co-author of the study, PhD, Principal Dinosaur Researcher of the University of Calgary and Assistant professor in the Department of Geoscience.
Study lead author Jared Voris, shown above, a PhD student of Zelenitsky’s whose analysis identified the new species, says the fossil specimen is very important to understanding the Late Cretaceous period when tyrannosaurs roamed the Earth. It gives us a new understanding of tyrannosaur evolution and how these animals interacted with their ecosystem.
“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,” says study co-author Dr. François Therrien, PhD, 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 research team also included Dr.Caleb Brown, PhD, curator of dinosaur systematics and evolution at the Royal Tyrrell and a co-author of the study.
Thanatotheristes degrootorum is named after John and Sandra De Groot, who found the fossils.
The team’s study, “A New Tyrannosaurine (Theropoda: Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, Provides Insight into the Evolution and Biogeography of Tyrannosaurids,” is published in the peer-reviewed journal Cretaceous Research.
New species have distinct physical features
Thanatotheristes degrootorum, a new genus and species, was identified from a fragmentary fossil consisting of parts of the skull and the upper and lower jawbones. The bones, which had apparently tumbled from a cliff and shattered on the shore of the Bow River, were found by John and Sandra De Groot (after whom the new species was named) in 2010 near the town of Hays, about 200 kilometres southeast of Calgary.
The specimen lay in a drawer at the Royal Tyrrell Museum until last spring, when Voris examined it. “We found features of the skull that had not been seen before in other tyrannosaurs,” he says. “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 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, Voris says.
Research indicates diversity among tyrannosaurs
Thanatotheristes, which Voris estimates were approximately eight metres long, likely preyed on large plant-eating dinosaurs, such as the horned Xenoceratops and the dome-headed Colepiochephale that were part of the ecosystem.
The differences in size, skull shape and other physical features among tyrannosaur groups from various geographical regions may be adaptations to different environments, available prey type and hunting strategies, Zelenitsky says.
“Some species are better suited to certain environments,” Voris says. “This reduces competition and gives species a better chance of survival.”
Such “provinciality” can also be seen in modern ecosystems with lions and tigers, he adds. Lions are found in Africa and favour open, savanna-type environments, while tigers are found in Asia and prefer forested environments.
Darla Zelenitsky, Jared Voris and François Therrien stand with the Thanatotheristes fossils.
Royal Tyrrell Museum
The team’s research also suggests tyrannosaurs didn’t share one general body type. Instead, groups of different tyrannosaur species evolved distinct skull forms, body sizes and other physical features, spreading into different environments where each group thrived.
“The next step is to test that hypothesis further and compare how tyrannosaur species from various geological regions differed,” Voris says.
The team’s research was supported by the Natural Sciences and Engineering Research Council of Canada, an Eyes High Doctoral Recruitment Scholarship for Voris, and the Royal Tyrrell Museum Cooperating Society.