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An 80-year debate among paleontologists has just ended: Nanotyrannus was not a T. rex cub, but rather a distinct predator that lived alongside it — more agile, with larger claws, and ten times lighter
Since 1942, when a mysterious skull was unearthed in the Hell Creek Formation, in Montana, United States, paleontologists debated whether that fossil belonged to a young Tyrannosaurus rex or a completely different species.
The debate lasted eight decades.
Now, studies published in the journals Nature and Science between 2024 and 2025 have proven that Nanotyrannus lancensis — the “dwarf tyrant” — was indeed its own species of tyrannosaurid.
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According to Christopher Griffin, a paleontologist at Princeton University, analysis of the original fossil’s throat bone revealed growth rings indicating a mature individual aged 15 to 18 years.
“The main discovery is that the holotype specimen represents a mature individual and therefore cannot belong to an immature Tyrannosaurus rex,” Griffin stated.
Ten times lighter than T. rex, but with larger claws
The Nanotyrannus measured between 5 and 9 meters in length and weighed 1 to 2 tons.
For comparison, an adult T. rex reached 12 meters and could weigh up to 9 tons.
That is, the Nanotyrannus had one-tenth the mass of its giant cousin.
But it wasn’t just a smaller version.
The finger bones and claws of Nanotyrannus were proportionally larger than those of T. rex.
This suggests it was an agile hunter, likely capable of grasping prey with its hands — something the T. rex, with its short and famously useless arms, could not do.
While the T. rex dominated by brute size, the Nanotyrannus competed with speed and precision.
The story of the fossil that went by three names in 80 years
The original skull was found in 1942 by researchers from the Cleveland Museum of Natural History.
In 1946, paleontologist Charles W. Gilmore described it as Gorgosaurus lancensis.
Forty-two years later, in 1988, Robert T. Bakker reclassified the specimen and created the name Nanotyrannus — “dwarf tyrant.”
At the time, Bakker estimated the animal measured 5.2 meters at the time of death.
But in 1999, Thomas Carr argued that it was merely a juvenile T. rex.
In 2020, Holly Woodward reinforced this theory by showing that the specimens were ontogenetically immature.
The pendulum only swung the other way in 2024.
The proof that ended the debate: rings in the throat bone
The turning point came when Christopher Griffin, from Princeton University, decided to analyze the hyoid — a small throat bone — from the original 1942 skull.
Using tomography and thin sections, he found annual growth rings.
These rings function like tree rings: each one represents a year of life.
The result showed that the animal was between 15 and 18 years old — it was already an adult.
If it were a young T. rex of that age, it should have been much larger.
A 15-year-old T. rex would already weigh several tons and measure over 8 meters.
The fact that the specimen was mature and yet small proved it was a different species.
“There’s no way to scientifically defend that this is a T. rex,” said James Napoli, from the North Carolina Museum of Natural Sciences.
Two apex predators in the same territory
The confirmation of Nanotyrannus as its own species has important implications.
It means that at the end of the Cretaceous, 67 million years ago, two large carnivorous predators coexisted in the same region.
The T. rex occupied the absolute top of the food chain.
The Nanotyrannus, lighter and faster, probably hunted smaller prey or competed for different niches.
It’s like lions and leopards sharing the savanna — the larger dominates, but the smaller survives through agility.
Researchers have already identified a possible second species of the genus: Nanotyrannus lethaeus, based on the fossil known as “Jane.”
The “Dueling Dinosaurs” fossil that helped solve the case
One of the most important specimens for resolving the debate was the so-called “Dueling Dinosaurs.”
Found in the Hell Creek Formation, it shows a Nanotyrannus and a herbivorous dinosaur preserved together, as if they had died in combat.
This fossil preserved rare parts, including the complete tail of the Nanotyrannus.
Lindsay Zanno, from the North Carolina Museum of Natural Sciences, used this specimen — nicknamed “Bloody Mary” — to confirm that it was an adult Nanotyrannus.
Analysis of more than 200 fossils from the region reinforced the conclusions.
Why it matters: the Cretaceous was more diverse than we thought
If Nanotyrannus is definitively confirmed as a valid genus, this changes the understanding of the Late Cretaceous ecosystem.
Previously, it was believed that the T. rex was the only large predator in North America during this period.
Now, the carnivorous fauna was more diverse than imagined.
This brings the North American Cretaceous ecosystem closer to the Asian model, where multiple species of tyrannosaurids coexisted in Mongolia.
Paleontology gains a missing piece in the puzzle of dinosaur extinction.
What could still change
Despite the new evidence, not all paleontologists are convinced.
The previous consensus, which lasted from 1999 to 2023, favored the juvenile T. rex theory.
Few complete Nanotyrannus skeletons have been found so far.
New discoveries in the Hell Creek Formation could reinforce or complicate the classification.
Still, the evidence published in Nature and Science is considered robust by the scientific community.
Nanotyrannus, after 80 years in the shadow of the T. rex, finally has its identity recognized.
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