Paleontologists have examined an exceptionally well-preserved, close to somatically mature tyrannosaur skeleton from the Hell Creek Formation of Montana. Their outcomes present that the specimen shares options with the holotype specimen of Nanotyrannus, and show that this lineage is distinguishable from Tyrannosaurus.
A pack of Nanotyrannus overtly assaults a juvenile Tyrannosaurus rex. Picture credit score: Anthony Hutchings.
“This fossil flips a long time of Tyrannosaurus rex analysis on its head,” stated Dr. Lindsay Zanno, a researcher at North Carolina State College and the North Carolina Museum of Pure Sciences.
Utilizing development rings, spinal fusion information and developmental anatomy, the researchers demonstrated that the brand new specimen was round 20 years previous and bodily mature.
Its skeletal options — together with bigger forelimbs, extra tooth, fewer tail vertebrae, and distinct cranium nerve patterns — are options fastened early in growth and biologically incompatible with Tyrannosaurus rex.
“For Nanotyrannus to be a juvenile Tyrannosaurus rex, it will must defy every thing we find out about vertebrate development. It’s not simply unlikely — it’s not possible,” stated Dr. James Napoli, a researcher at Stony Brook College.
For years, paleontologists have used Nanotyrannus fossils to mannequin Tyrannosaurus development and habits.
This new proof reveals that these research have been primarily based on two totally completely different animals — and that a number of tyrannosaur species inhabited the identical ecosystems within the ultimate million years earlier than the asteroid influence.
As a part of their analysis, Dr. Zanno and Dr. Napoli examined over 200 tyrannosaur fossils.
They found that one skeleton, previously thought to characterize a teenage Tyrannosaurus rex, was barely completely different than the previously-described species Nanotyrannus lancensis, which is a part of the well-known Dueling Dinosaurs fossil.
The authors concluded that the specimen represents a brand new Nanotyrannus species and named it Nanotyrannus lethaeus.
Affirmation of the validity of Nanotyrannus implies that predator range within the final million years of the Cretaceous interval was a lot increased than beforehand thought, and hints that different small-bodied dinosaur species may additionally be victims of mistaken id.
“This discovery paints a richer, extra aggressive image of the final days of the dinosaurs,” Dr. Zanno stated.
“With monumental dimension, a robust chew pressure and stereoscopic imaginative and prescient, Tyrannosaurus rex was a formidable predator, but it surely didn’t reign uncontested.”
“Darting alongside was Nanotyrannus — a leaner, swifter and extra agile hunter.”
The findings seem at this time within the journal Nature.
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L.E. Zanno & J.G. Napoli. Nanotyrannus and Tyrannosaurus coexisted on the shut of the Cretaceous. Nature, revealed on-line October 30, 2025; doi: 10.1038/s41586-025-09801-6
