The discovery supports the thesis that the great Tyrannosaur emerged in North America
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The discovery supports the thesis that the great Tyrannosaur emerged in North America
10:25 AM • March 17 2026 IST
A shin bone found in New Mexico belonged to an early but unusually large tyrannosaur, according to new analysis of an old bone published Thursday in Scientific Reports.
How big is an "unusually large tyrannosaur"? Its shinbone is 96 centimeters long, more than three times longer the corresponding human equivalent.
It's not the longest tyrannosaur shinbone ever discovered: That honor remains with Sue, whose shin was estimated to have stretched somewhere between 112 to 120 centimeters in length.
The newly reported animal lived about 74 million years ago and was on the large side as tyrannosaurs went. Early tyrannosaurids tended to be smallish, such as China's Dilong paradoxus which was just two meters in length and lived about 130 million years ago – any self-respecting saltwater crocodile today is double that and counting. But mainly, this new dinosaur adds to other Tyrannosaurinae variants identified in New Mexico and Texas.
There is an argument to this day about where Tyrannosaurus evolved – in what are today Asia or North America. The authors propose that their dinosaur had a common ancestor with these other Tyrannosaurinae, and suggest these discoveries together support the thesis that Tyrannosaur emerged in what is today North America.
The newly reported remains were found in the Kirtland Formation, New Mexico and date to about 74 million years ago, a time called the Late Campanian age in the Late Cretaceous, explain Nicholas Longrich of the University of Bath, UK and colleagues in the article.
Based on the actual bones and postulated tyrannosaurid dimensions, the team estimates that the animal weighed about 4.7 tons, making it the largest known tyrannosaur from its period.
We note that Sue lived in South Dakota seven million years later and is estimated to have weighed at least double that. (Was Sue actually female? Identifying gender from fossils is notoriously difficult and in this case, paleontologists point to the animal's medullary bone which is more typical of les femmes dinosaures than les hommes, but the answer is – we don't know if Sue was female.)
Whatever Sue was, the authors suggest that new tyrannosaur may be an early member of Tyrannosaurinae (or Tyrannosaurini) – a group of specifically large tyrannosaurs. The group includes Tyrannosaurus rex itself as well as Tarbosaurus of Mongolia and Zhuchengtyrannus, known from Late Cretaceous China.
Tyrannosaurinae were variations on a theme, famed for their large heads and teeth, towering height and tiny, seemingly vestigial forelimbs. The earliest known is Lythronax which lived about 82 million years ago.
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, further study is needed and more specimens of this type would be helpful.
Meanwhile it seems that Tyrannosauridae emerged as the dominant predators in the supercontinent of Laurasia in the Late Cretaceous, about 68 millionyears ago. In North America, they replaced other large carnivores such as Albertosaurinae which look like T-rexes, Daspletosaurinae which look like T..rexes, and Teratophonei – guess what they looked like?
But all those weighed only two to three tons and when tyrannosaurini got big, they weighed over 10 tons.
The one reported today was a big one. Was it a hitherto unknown species? Maybe. It could be an unusually beefy Bistahieversor (which looked like a T.rex), an early Tyrannosaurinae (ditto) or a previously unknown species of tyrannosaur, the team suggests, but it's leaning towards it being an early Tyrannosaurinae based on its sheer size, robust proportions, and the shape of the distal shaft. So, a close relative of the famed Tyrannosaurus rex of which Sue was a member.
Apropos newly discovered tyrannosaurids, just last December, the decades-long argument over what wee Nanotyrannus lancensi may have been resolved.Nanotyrannus is not, repeat not, a teenage T. rex or a baby or a dwarf. It is a proud stand-alone small-sized tyrannosaur that lived in Cretaceous North America, Christopher Griffin and colleagues reported.
The latest opinion, that Nanotyrannus was not a juvenile rex, was based on analysis of ceratobranchial throat bones. In birds and reptiles today, the ceratobranchial bone evinces signals of growth and maturity, helping science to determine a given animal's developmental stage.
Conclusion: The toothy predator Nanotyrannus may have been small, no bigger than a Great Dane standing on its hind legs, but it was adult or approaching it. Tyrannosauruses, as a group, were not entirely as we have been thinking.
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