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Palaeontology: Study ends decades-long dispute over Nanotyrannus
A new fossil from Montana is causing a stir in the world of palaeontology: a comprehensive study has settled the long-standing debate about the so-called ‘juvenile Tyrannosaurus rex’. The result: the supposedly young specimens do not belong to the family of the famous predatory dinosaur – they are representatives of their own genus, Nanotyrannus.
A discovery that rewrites the history of tyrannosaurs
An exceptionally well-preserved Tyrannosaurus skeleton has been discovered in the middle of the Badlands of Montana. What was initially thought to be another ‘teenage T. rex’ turned out, after intensive analysis, to be an adult representative of a previously controversial genus. In the journal Nature, researchers present evidence that the animal differs significantly from Tyrannosaurus rex in almost every bone.
The finest differences in skull structure, nerve pathways and limbs reveal that this animal was not a juvenile, but a fully grown specimen. This disproves one of the most persistent theories in palaeontology – the assumption that smaller tyrannosaurs were merely immature T. rexes.
‘The evidence has always been there, but now it’s overwhelming,’ says British palaeontologist Nicholas Longrich. ‘This specimen differs from the T. rex in almost every bone in its body.’
Nanotyrannus: From taboo subject to recognised species
The name Nanotyrannus is a controversial term in scientific history. Since its first description in 1946 by US palaeontologist Charles Gilmore, the ‘dwarf tyrannosaur’ has been considered a questionable classification. For decades, the prevailing opinion was that it was merely a juvenile T. rex – until now.
The new study not only confirms the independence of Nanotyrannus, but also suggests that there may have been two different species within this genus.
‘Nanotyrannus is real – and that forces us to completely rethink the evolution of tyrannosaurs,’ explains Steve Brusatte, palaeontologist at the University of Edinburgh.
The turning point: the ‘duelling dinosaurs’
The key specimen comes from the so-called ‘Duelling Dinosaurs’ site, which was acquired by the North Carolina Museum of Natural Sciences in 2021. The fossils – around 30,000 pounds of bone and rock – show a Nanotyrannus and a Triceratops that apparently died in battle.
Detailed examination revealed several anomalies: for example, the hand of the supposedly young T. rex was larger than that of a fully grown T. rex – a clear sign that it could not have been the same animal.
Analysis of the growth rings in the bones also confirmed that the animal was about 20 years old and fully grown. So it was not a young animal – but a small, agile predator species that lived at the same time as the gigantic T. rex.
The Jane case: A second Nanotyrannus
The research team led by Lindsay Zanno and James Napoli then examined more than 120 known fossils and came across further surprises. The well-known skeleton ‘Jane’, long considered to be a juvenile T. rex, turned out to be a representative of a second Nanotyrannus species.
It was given the scientific name Nanotyrannus lethaeus – named after the mythological river Lethe, whose waters bring forgetfulness. ‘A fitting name for an animal that remained hidden from view for decades,’ said Zanno.
Not all researchers are convinced. US palaeontologist Thomas Carr, who long argued that Nanotyrannus was a young T. rex, now at least acknowledges that the new specimen represents a separate species. But he remains sceptical that ‘Jane’ is a second species.
‘Science means being willing to give up your beliefs when new evidence emerges,’ says Carr. ‘I thought we had the answer – but apparently we still know very little about the evolution of tyrannosaurs.’
Why the dispute lasted so long
One reason for the decades of uncertainty is that many fossils of young T. rex are privately owned and not accessible to researchers. This meant that important comparative samples were missing. In addition, the topic was politically charged in academic palaeontology – proponents of the Nanotyrannus concept were often considered outsiders.
‘Some of my colleagues even made fun of us online,’ recalls Peter Larson, who has believed in the existence of Nanotyrannus since the 1990s. ‘Now the tide seems to have turned.’
A new look at the Cretaceous period
If the new findings are confirmed, it means that 67 million years ago, at least two species of tyrannosaur roamed the North American plains – the massive, multi-ton Tyrannosaurus rex and the smaller, faster Nanotyrannus.
‘Nanotyrannus was probably more agile and hunted different prey than the T. rex,’ says Longrich. ‘It was the predator that stood between Velociraptor and T. rex – a true medium-sized hunter.’
And while experts are still sorting things out, Longrich is delighted with the new insights: ‘The beauty of science is that it constantly reminds us how little we know. Nanotyrannus is real – and it makes the Cretaceous period a lot more exciting.’
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