Discovery of T. rex’s cousin upends our understanding of tyrannosaur evolution

A new species of tyrannosaur has been discovered by scientists in Canada. Fossils of the carnivorous dinosaur, a cousin of Tyrannosaurus rex, suggest it lived 77 million years and was 8 metres long with lengthy, lean legs. This is a rare addition to an unusual branch of the tyrannosaur family tree and complicates our understanding of how these dinosaurs evolved. Tyrannosauridae, a family of dinosaurs, split into two subfamilies: tyrannosaurines, made up of T. rex and other stocky, heavy species with relatively long heads, and albertosaurines, which had relatively short skulls and lighter builds. When the first foot fossils of this new predator were uncovered by researchers in southern Alberta, Canada, in 2010 and 2011, it was unclear what subfamily of tyrannosaur they belonged to, says Mark Powers at the University of Alberta. As more of the skeleton has been unearthed and researchers have found additional specimens, it seems that the mysterious dinosaur had features of both. Advertisement Now, Powers and his colleagues have measured its bones and compared the dimensions to other tyrannosaur species. They found that the newly discovered dinosaur had a hole near the front of its upper jaw, like that in the robust Daspletosaurus, a tyrannosaurine – but it also had a small sinus system like Gorgosaurus libratus, an albertosaurine. “It was just so different and so unique that it was very clearly a new species,” says Powers. The researchers’ analysis classified the strange predator as an early member of the albertosaurine group and named it Tromerosaurus solumons. Tromerosaurus means “frightful lizard”, a homage to similar translations of Daspletosaurus and Gorgosaurus. Solumons means “lonely mountain”, a reference to the isolated horn over its eye and to the lair of Smaug, the dragon in J.R.R. Tolkien’s The Hobbit. “Tyrannosaurs do have very similar iconography to dragons,” says Powers. The mixture of features in Tromerosaurus may spur the need to re-examine whether other tyrannosaurs have been properly classified, says Powers. The criteria for defining the subfamilies might be less informative than scientists thought, he says. The discovery also sheds new light on the evolution of tyrannosaur diversity. “Rather than the stepwise growth into T. rex as the culminating endpoint to tyrannosaurs, it might be a bit more complicated than that,” says Powers. “There might be multiple tyrannosaur lineages that continue on until the end-Cretaceous.” Jared Voris at the University of Calgary in Canada says that examining fossils of even earlier albertosaurine species can help researchers iron out their evolutionary story. “We need to go deeper in the rock record,” says Voris. “What will the tyrannosaur species we find in 78- to 79-million-year-old rocks show us?” Journal of Vertebrate Paleontology DOI: 10.1080/02724634.2026.2728669 Dinosaur hunting in the Gobi desert: Mongolia Embark on an exhilarating and one-of-a-kind expedition to uncover dinosaur remains in the vast wilderness of the Gobi desert, one of the world’s most famous palaeontological hotspots.