For 40 years, dinosaur experts have been locked in a huge debate over diminutive fossils found in the Western United States. Did they belong to a teenage version of Tyrannosaurus rex, or to another species in the tyrannosaur family entirely?

A new study may have settled the dispute. Paleontologists said in the journal Nature on Thursday that a fossil specimen in a North Carolina museum belonged to Nanotyrannus lancensis, part of a distinct group of tyrannosaurs.

“We have this animal that’s been hiding in plain sight, and it raises all kinds of questions that we as paleontologists weren’t asking until now,” said Lindsay Zanno, a paleontologist at the North Carolina Museum of Natural Sciences and an author of the study.

In the 1980s, fossil hunters found a small tyrannosaur skull from the

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