Palaeontology: An unusually large North American tyrannosaur (Scientific Reports)
13 March 2026
The discovery of a leg bone belonging to an unusually large tyrannosaur — the group of dinosaurs that includes Tyrannosaurus rex — is described in a study published in Scientific Reports. The authors suggest that the tyrannosaur may represent an early member of Tyrannosaurini — a group of large tyrannosaurs including Tyrannosaurus, Tarbosaurus, and Zhuchengtyrannus.
Nicholas Longrich and colleagues examined the fossilised shinbone after it was previously discovered in the Kirtland Formation, New Mexico, USA. Based on the age of this formation, they date the bone to 74 million years ago in the Late Campanian age. The shinbone is 960 millimetres long and 128 millimetres in diameter, which the authors note is 84% the length and 78% the diameter of the shinbone of the largest known Tyrannosaurus, known as ‘Sue’. They propose that the bone may belong to a close relative of Tyrannosaurus based on its large size, dimensions, straight shaft, and the triangular shape of its lower end. Based on its dimensions, they estimate that the tyrannosaur weighed approximately 4,700 kilograms, which would make it the largest tyrannosaur from this period reported so far. By comparing the characteristics of the shinbone with those of other tyrannosaurs, the authors propose that it may have shared a common ancestor with T. rex and Tyrannosaurus mcraeensis and speculate that it may have been an early member of the Tyrannosaurini group.
The authors suggest that the discovery of this bone, along with previous discoveries of giant Tyrannosaurus-like dinosaurs — including T. mcraeensis — in New Mexico and Texas, could support the hypothesis that Tyrannosaurus may have evolved in what is now southern North America. However, they note that further study of the dinosaur record in this region is needed. Additionally, more complete remains are needed for definitive identification of the dinosaur, its relationships with other tyrannosaurs, and more accurate estimates of its size.
- Article
- Open access
- Published: 12 March 2026
Longrich, N.R., Dalman, S., Lucas, S.G. et al. A large tyrannosaurid from the Late Cretaceous (Campanian) of North America. Sci Rep 16, 8371 (2026). https://doi.org/10.1038/s41598-026-38600-w
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