For almost 30 years, paleontology has been divided by a fascinating dilemma: did Nanotyrannus exist or was it just a young version of Tyrannosaurus rex? Now, a study led by Lindsay E. Zanno and James G. Napoli provides compelling evidence that tips the balance. After analyzing the fossils known as the “dueling dinosaurs,” the researchers conclude that the alleged adolescent T. rex was not such, but a completely different predator.
The discovery that reopened an old discussion
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In 2006, a group of amateur fossil hunters discovered in the Hell Creek Formation (Montana, USA) the remains of a juvenile Tyrannosaurus rex and an adult Triceratops, apparently caught in the middle of a fight 67 million years ago.
Both were buried together, probably by a flood or a sandslide, and went down in history as the “grieving dinosaurs.”
Almost two decades later, the study published in Nature reviews that finding and offers a completely different interpretation: the predator was not a young T. rex, but an adult specimen of a separate species, Nanotyrannus lethaeus.
A controversy that has been going on for more than 30 years
The debate about Nanotyrannus began in 1942, when a tyrannosaur skull was discovered in the same geological formation.
It was initially classified as Gorgosaurus, but in 1988 it was reidentified as Nanotyrannus lancensis. Many experts, however, considered it a mistake, arguing that it was simply a growing T. rex.
Since then, the scientific community has been divided: some defended that the smallest specimens belonged to a different species; others, that they were juveniles of the most iconic predator of the Cretaceous.
The evidence that changes the story
When the North Carolina Museum of Natural Sciences acquired the fossil in 2020, Zanno and Napoli’s team was able to examine it in detail and compare it to more than 200 tyrannosaur skeletons.
The result was revealing: the supposed juvenile T. rex showed longer forearms, more teeth and fewer caudal vertebrae than Tyrannosaurus rex.
These differences do not correspond to maturity or growth, but to fixed anatomical features, typical of another species. In addition, analyzes of the bones of its legs indicated that the animal was around 20 years old when it died, which rules out that it was a young specimen.
In other words, it was already an adult, but smaller, more agile and with different proportions than the giant T. rex.
The reinterpretation of the “Jane” fossil
The study also reviews the famous skeleton known as Jane, found in 2001 and preserved at the Burpee Museum of Natural History (Illinois). Until now it was believed to represent a juvenile T. rex, but new comparisons place it within the same category as Nanotyrannus lethaeus.
The name of the species—from the Latin Lethaeus, in reference to the river of oblivion in Greco-Roman mythology—alludes to the “rebirth” of the fossil: a reinterpretation that erases its previous identity to give it a new one.
Two predators, two strategies
If Tyrannosaurus rex and Nanotyrannus coexisted, they must have shared an ecosystem without directly competing. Researchers maintain that Nanotyrannus was a pursuit hunter, capable of running long distances and catching fast prey.
The T. rex, for its part, would have been a slower but more powerful ambush predator, specializing in large or injured animals.
This ecological balance would explain how both species were able to thrive simultaneously in North America during the last million years of the Cretaceous.
A new page in the history of the Cretaceous
Zanno and Napoli’s study not only revives the name Nanotyrannus, but also provides a more complex look at the diversity of tyrannosaurs.
Far from being a simple “adolescent T. rex,” this small predator would represent a parallel and more agile branch within the family of large Cretaceous carnivores.
If confirmed with future findings, Nanotyrannus lethaeus would become one of the greatest taxonomic readjustments in recent paleontology, giving us a much more varied ecosystem than was believed in the last days of the dinosaurs.
Source: Infobae.