Return of the short (tyrant) king: A new paper by Dinosaur Institute researcher shows Nanotyrannus was not a juvenile T. Rex
Peer-Reviewed Publication
Updates every hour. Last Updated: 9-Dec-2025 12:12 ET (9-Dec-2025 17:12 GMT/UTC)
For decades, paleontologists argued over the lone skull used to establish the distinct species Nanotyrannus. Was it truly a separate species or simply a juvenile Tyrannosaurus rex? A new paper published in Science has definitively shown that Nanotyrannus is, in fact, nearly fully grown and not an immature T. rex, at the same time revealing new insights into how these giant predators achieved such terrifying sizes so quickly.
A multi-institutional team, including Dinosaur Institute Postdoctoral Fellow, Dr. Zach Morris, examined the much-debated Nanotyrannus holotype—the specimen used to name a new species—particularly its throat bone. The team examined the bone’s microscopic structure, comparing it to those of living birds, crocodilians, and extinct dinosaurs—including the Dino Hall’s singular T. rex growth series—to establish that Nanotyrannus, while smaller, was a fully grown and distinct predator in an ancient ecosystem more diverse than previously imagined. Slightly less than half the size of their massive adult cousins, Nanotyrannus competed with juvenile T. rex for prey in Late Cretaceous North America.
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