DISCOVERY! Nanotyrannus isn't a 'mini T. Rex' after all — it's a new species, '

Here's another amazing scientific finding- a NEWLY discovered species of dinosaur called the Nanotyrannus. As someone who loved dinosaurs as a kid and had a little fossil collection and tons of plastic dinosaurs, I love palentology. So each time I read about a new species discovered, I have to share it!

(IMAGE: An illustration of a pack of Nanotyrannus dinosaurs attacking a young Tyrannosaurus rex. A new study finds that the controversial Nanotyrannus is a real species and not simply a juvenile T. rex. (Image credit: Anthony Hutchings)

Nanotyrannus isn't a 'mini T. Rex' after all — it's a new species, 'dueling dinosaurs' fossil reveals

By Chris Simms, Live Science, October 30, 2025

An argument over whether fossils from several small dinosaurs represent a juvenile Tyrannosaurus rex or smaller adults of a separate species may finally be settled.

A pivotal new dinosaur study is finally settling a fierce, four-decade-long debate: Was the small tyrannosaur Nanotyrannus a distinct species or merely a teenage Tyrannosaurus rex? Now, a remarkably complete fossil reveals that Nanotyrannus was real.

For years, key fossils were thought by many paleontologists to be juvenile examples of Tyrannosaurus rex, which lived between 67 million and 66 million years ago in western North America. Rather than settling all arguments, however, this "nano" discovery opens a new chapter in understanding T. rex biology and further debate.

A key source of the argument has been a small 67 million-year-old tyrannosaur skull found in the Hell Creek Formation of Montana in 1942. It was given its own species name Nanotyrannus lancensis, in 1988, meaning that the species was based on a single skull, and no one knew what the rest of its body looked like.

"This has been one of the most controversial topics in all of dinosaur paleontology," study co-author Lindsay Zanno, a paleontologist at North Carolina State University and North Carolina Museum of Natural Sciences, told Live Science.

Apart from the isolated skull, the best skeleton of one of these small-body tyrannosaurs came from the Hell Creek Formation, which also spans parts of North Dakota, South Dakota and Wyoming. This specimen, known as Jane, was still rapidly growing and aged about 11 when it died, and differed in several ways from the lone skull.

Now, Zanno and study co-author James Napoli, an anatomist at Stony Brook University in New York, have described a complete tyrannosaur skeleton that is part of the "Dueling Dinosaurs" fossils, the 67 million-year-old remains of what seemed to be the most complete, yet small, T. rex on record and a Triceratops, possibly locked in combat when they died.

(IMAGE: Study co-author Lindsay Zanno, a paleontologist at North Carolina State University and and head of paleontology at the North Carolina Museum of Natural Sciences, sits next to the famous "Dueling Dinosaurs" specimen from the Hell Creek Formation of eastern Montana. (Image credit: N.C. State University)

The case for Nanotyrannus

Zanno and Napoli say this "Dueling Dinosaurs" skeleton of a tyrannosaur, also from the Hell Creek Formation, isn't a T.  rex and instead shares features with the N. lancensis skull. Crucially, their analysis of growth rings in the bones, spinal fusion data and developmental anatomy indicates that the fearsome dinosaur was about 20 years old and almost fully grown when it died, rather than being a juvenile.