Nanotyrannus: the skeleton of a dinosaur settles a long debate on the fossils of the “little T. rex”

A dinosaur fossil believed to be juvenile Tyrannosaurus rex is actually an adult carnivore of a different species, according to researchers who believe they have finally settled a fierce and long-running debate in paleontology.

The dispute stems from a skull discovered in Montana’s Hell Creek Formation in the 1940s, originally classified as a Gorgosaurusthen suggested being a minor T. rex. In 1988, other researchers claimed that the fossil was actually an adult of a smaller, related species, which they named Nanotyrannus lanceensis.

A number of additional fossils have since been identified as Nanotyrantbut many paleontologists believe they are actually miners T. rex specimens.

Now, for the first time, researchers have analyzed a complete skeleton that appears to show beyond doubt that Nanotyran is a distinct species.

The skeleton is one of a pair of fossil specimens dubbed the “duel dinosaurs”, which was discovered by commercial fossil hunters in 2006. The fossil features a Triceratops buried alongside what was originally thought to be a miner T. Rex about 67 million years ago.

It wasn’t until 2020, when the fossil was purchased by the North Carolina Museum of Natural Sciences, that paleontologists were able to comprehensively study the remains.

“When we acquired the specimen, we knew it was exceptional,” says Lindsay Zanno of the North Carolina Museum of Natural Sciences. “Little did we know that this would upend decades of research into the world’s most famous dinosaur.”

Zanno, who conducted the analysis with colleague James Napoli of Stony Brook University in New York, says she initially joined the juvenile delinquency program. T. rex theory, but the evidence forced her to reconsider her decision.

“Nanotyran has different nerve and sinus configurations in the skull, more teeth, larger hands and a shorter tail,” she says. “We know that these characteristics don’t change as animals grow from baby to adult.”

According to Zanno and Napoli, detailed analysis of the dinosaur’s limb bones confirms that it was an adult individual around 20 years old, weighing around 700 kilograms and measuring around 5.5 meters long. “This is about a tenth of the body mass and half the length of a full-grown adult. Tyrannosaurus“, says Zanno.

Zanno and Napoli also reanalyzed 200 tyrannosaur fossils and concluded that another nearly complete skeleton from the Hell Creek Formation, known as Jane, which was thought to be a T. rex adolescent, was also misclassified. It is said that Jane is actually a new species in the genus Nanotyranthat they call Nanotyrannus letaeus.

“We only have one skeleton of N. lethaeus“, but its anatomy suggests that it was a larger species,” says Zanno. “The patterns of the sinuses in the palate and the shape of the bone behind the eye are unique.”

Scott Persons of the South Carolina State Museum says new study resolves debate over Nanotyran being a distinct genus and species.

“For my money, Nanotyran was one of the scariest dinosaur predators,” Persons says. “It’s the one I would least like to be chased by. It had extremely long legs and was armed with a wicked thumb claw.

“We can think of Nanotyran And Tyrannosaurus as analogous to modern cheetahs and lions. Yes, they have a generally similar body plan, but they were specialized for different ways of hunting.

Thomas Carr of Carthage College in Wisconsin, who long served on the T. rex camp, says the new evidence is “pretty conclusive” that the Dueling dinosaur specimen is a “near-adult of a species that is not T. rex“.

And Holly Ballard of Oklahoma State University, who led a 2020 study refuting the Nanotyran ” says she “agrees” with the team’s conclusion that the fossil is that of an individual approaching adult size.

But neither Ballard nor Carr are convinced that the other fossil, Jane, represents a new Nanotyran species. “Jane continues to grow and is already taller than N. lancensistherefore say that it is a new taxon instead of a juvenile T. rex“, says Ballard. “We’re back to the same old debates.”

“On top of that, if every little tyrannosaur in the Hell Creek Formation is Nanotyranso where are the miners T. rex” says Carr. “That part of the picture doesn’t add up. In terms of fossils, we simply haven’t collected enough tyrannosaurs from the Hell Creek Formation to really understand what was happening during the early stages of growth of T. rex.»

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