The Digester

Detailed study of a complete small tyrannosaur skeleton from the Duelling Dinosaurs shows anatomical and growth evidence that supports Nanotyrannus as a separate adult species, though some experts still dispute whether all small Hell Creek tyrannosaur fossils are distinct from juvenile T. rex.

New analysis of the Duelling Dinosaurs specimen shows the small carnivore is a grown Nanotyrannus rather than a juvenile Tyrannosaurus rex.
Researchers identified different skull nerve and sinus patterns, more teeth, larger hands and a shorter tail that are not explained by growth from juvenile to adult T. rex.
Limb bone analysis indicates the individual was about 20 years old, roughly 700 kilograms and 5.5 metres long, about one tenth the mass and half the length of a full grown T. rex.
A reanalysis of roughly 200 tyrannosaur fossils led the team to designate a second species, Nanotyrannus lethaeus, based on the
Jane
specimen.
Some paleontologists accept the new conclusions while others remain unconvinced that all small Hell Creek tyrannosaurs are distinct species rather than juvenile T. rex.
The Duelling Dinosaurs were found in 2006 and became available for full study after the North Carolina Museum of Natural Sciences purchased the specimen in 2020.

Complete skeleton supports Nanotyrannus as a distinct small tyrannosaur, not a juvenile T. rex

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