Scientists thought this was a young T. rex. They were wrong
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Scientists thought this was a young T. rex. They were wrong
Not a teen T. rex after all—Nanotyrannus may have been its own fierce, pint-sized predator.
Date:
April 15, 2026
Source:
University of Nebraska-Lincoln
Summary:
A long-running dinosaur mystery may finally be solved: Nanotyrannus, once dismissed as just a teenage T. rex, appears to have been its own distinct species after all. Scientists analyzed a tiny throat bone from the original fossil and discovered growth patterns showing the animal was already mature, not a juvenile giant-in-the-making. This smaller predator—about half the size of a full-grown T. rex—likely roamed alongside its famous cousin, adding a new layer of complexity to prehistoric ecosystems.
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A cast of a Nanotyrannus skull was on exhibit at the Cleveland Museum of Natural History in Cleveland, Ohio. The fossil skull is the holotype for Nanotyrannus lancensis. Credit: Tim Evanson, Wikimedia Commons
A long-running scientific debate may finally be nearing its end. New research involving the University of Nebraska State Museum's Ashley Poust provides strong evidence that Nanotyrannus, often described as a smaller version of Tyrannosaurus rex, was in fact a real and separate species.
The research team, led by Christopher Griffin of Princeton University, focused on the original Nanotyrannus fossil, a skull housed at the Cleveland Museum of Natural History. To determine the animal's age at death, they examined a rarely studied bone known as the ceratobranchial, or hyoid, which was preserved with the skull.
Using bone histology, or the study of fossilized bone microstructure, the team analyzed this small throat bone and identified growth patterns that indicate the animal had reached or was close to full maturity. This finding is critical because it shows the specimen was not a young Tyrannosaurus rex still growing.
These findings were published in Science.
"This small-bodied -- in relation to the T. rex -- meat-eater's hyoid bone showed growth patterns that suggest maturity or approaching maturity," said Poust, Voorhies Endowed Curator of Vertebrate Paleontology. "This lets us be confident in keeping the name Nanotyrannus, because this animal is clearly not on a growth path to becoming a Tyrannosaurus rex."
A Much Smaller Predator
Estimates suggest Nanotyrannus reached about 18 feet in length, making it significantly smaller than a full-grown T. rex, which could exceed 40 feet. This size difference supports the idea that it was not simply a younger stage of the larger species.
A Fossil With a Complicated History
The Nanotyrannus skull was first discovered in 1942 and initially classified as Gorgosaurus. In 1988, further study led scientists to rename it Nanotyrannus lancensis. However, many researchers later argued that it was actually a juvenile T. rex, fueling decades of debate.
The new findings challenge that long-standing assumption.
"At the time, the prevailing consensus was that the Nanotyrannus holotype skull represented an immature Tyrannosaurus rex, and was not a separate species," said Griffin, assistant professor of geosciences at Princeton. "Our expectations were simply following along with that consensus, but once we sampled the hyoid and saw features that strongly indicated maturity, we knew that we had to examine that idea more skeptically."
A New Method for Studying Dinosaur Growth
To strengthen their conclusions, Poust compared hyoid bones from a range of species, including modern relatives of dinosaurs (ostriches, alligators and lizards), as well as other fossil specimens. This approach had not previously been applied to dinosaur fossils and could open up new ways to study fragmentary remains.
"It's expanding, in a small way, the ability to learn about animals' past lives," Poust said. "It was exciting to show that the growth signal is so conserved across the body. Maybe this is a tiny wedge to start investigating that in some different ways."
Poust noted that he did not expect the hyoid to be such a reliable indicator of age. Traditionally, scientists rely on larger bones like ribs or femurs for this type of analysis, but the results suggest the hyoid may be just as useful.
Debate Likely Settled, New Questions Emerge
The question of whether Nanotyrannus existed as a separate species now appears largely resolved. This study follows closely on the heels of another recent paper in Nature that also examined a possible Nanotyrannus fossil discovered in Montana and now housed at the North Carolina Museum of Natural Sciences.
"We investigated the holotype specimen because it is the one fossil that formally defines the species -- any other specimens that are called Nanotyrannus lancensis are being referred to this one specimen, which holds the species name," Griffin said. "Since this specimen is mature, this definitively shows that Nanotyrannus is