Tiny Throat Bone Confirms Nanotyrannus as Own Species — Adding Another Predator to the Late Cretaceous

The identity of Nanotyrannus has long rested on an unresolved question: Was it its own small predator – or just a juvenile? Tyrannosaurus rex who hadn’t finished growing?

Now researchers say a small bone in the throat provided an answer. By analyzing the hyoid, located under the tongue and used to anchor the swallowing muscles, the team discovered that the Nanotyrannus had already reached, or almost reached, skeletal maturity when he died.

Published in Sciencethe results confirm that Nanotyrannus was a distinct species, not a young T. rex – while also revealing a powerful new way to determine a fossil’s age at death.

“This little body – compared to the T. rex “The meat-eater’s hyoid bone showed growth patterns that suggest maturity or near maturity,” Ashley Poust, Voorhies’ curator of vertebrate paleontology, said in a press release. “This allows us to make sure we keep the name. Nanotyrannusbecause this animal is clearly not on a growth path to becoming a Tyrannosaurus rex.”

THE Nanotyrannus The identity debate revisited

The hyoid was preserved intact with the skull when it was discovered in 1942. Since then, the fossil has had several identities. It was first classified as Gorgosaurus, then renamed Nanotyrannus lancensis in 1988, before being reinterpreted by numerous researchers as a Tyrannosaurus rex.

Last month, a fossil of dueling dinosaurs added new weight to the case that Nanotyrannus was its own species. But the discovery did not resolve a key uncertainty: how old the original reference fossil – the holotype skull housed at the Cleveland Museum of Natural History – actually was at the time of the animal’s death.

“At the time, the prevailing consensus was that Nanotyrannus the holotype skull represented an immature Tyrannosaurus rexand was not a distinct species,” said Christopher Griffin, assistant professor of geosciences at Princeton. “Our expectations simply followed that consensus, but once we sampled the hyoid and saw features that strongly indicated maturity, we knew we had to examine this idea with more skepticism.

A new tool for dating dinosaur fossils

Because the hyoid is small and fragile, it is rarely preserved – and has never before been used as a primary aging tool for dinosaurs. Using bone histology, which analyzes frozen microscopic growth layers inside fossilized bones, the team discovered patterns that only appear in late stages of skeletal maturity.

To test whether the method was reliable, the researchers examined the hyoids of modern animals related to dinosaurs, including ostriches, alligators and lizards, as well as other dinosaur fossils. In all cases, the hyoid tracked age as consistently as traditional tools such as ribs and femurs.

“This expands, to some extent, the ability to learn about the past lives of animals,” Poust said. “It was exciting to show that the growth signal is so conserved throughout the body. Maybe this is a little corner to start studying this in different ways.”

An adult Nanotyrannus and Upper Cretaceous ecosystems

With the holotype now confirmed to be mature, the ecological picture of the Late Cretaceous becomes more complete. The adult Nanotyrannus was probably about 18 feet long – dwarfed by the 40+ foot length of T. rexbut remains a formidable predator in its own right.

“You end up with at least two different-sized meat eaters in the same environment, which has big implications for ecology and dinosaur extinction,” Poust said. “Learning more about what once existed gives us an idea of ​​the breadth of the fossil record and how species change over time. And understanding the complexity of an ecosystem is important.”

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