Nanotyrannus Officially a Separate Species – Not a Baby T.rex: The “Little Tyrant King” Returns!

In October 2025, two groundbreaking studies in Nature and Science officially ended a nearly 40-year-old debate: Nanotyrannus is not a baby T.rex, but a completely separate genus and species.

The lead study (Zanno & Napoli, Nature, October 30, 2025) analyzed the specimen “Dueling Dinosaurs” (NCSM 40000, nicknamed “Bloody Mary”) – a nearly complete tyrannosaur skeleton. The results showed it was a mature individual of Nanotyrannus lancensis, not a juvenile T.rex. The anatomical features (bone shape, number of teeth, forelimb structure, and bone tissue) are completely different and cannot be explained by age development.

More notably, the research team also described a new species: Nanotyrannus lethaeus (a name reminiscent of the River Lethe in Greek mythology – the “forgotten river”). Thus, at least two Nanotyrannus species coexisted with T.rex in the Hell Creek Formation 66–67 million years ago.

An additional study in Science (December 2025) using hyoid bones to determine maturity confirmed that the Nanotyrannus specimens were mature individuals, not “teen rex”.

Nanotyrannus was a smaller (about 5–6 meters long), agile, long-legged tyrannosaur, suited to swift hunting rather than direct confrontation with the giant T.rex. The coexistence of two tyrannosauroid genera at the end of the Cretaceous period suggests that the North American dinosaur ecosystem was far more complex than previously thought.

As of June 2026, Nanotyrannus has been widely recognized as a valid genus. The “Little Tyrant” is officially back – no longer a baby T.rex, but a distinct, tiny yet extremely dangerous predator.