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Nature Study Confirms Adult Nanotyrannus in 'Dueling Dinosaurs,' Naming Second Species

The finding compels a reassessment of decades of T. rex growth studies that relied on misclassified small fossils.

Image
Lindsay Zanno, head of paleontology at the North Carolina Museum of Natural Sciences, poses with the famed dueling dinosaurs fossil.
The snout of Nanotyrannus, which has more teeth than T. rex.
While juvenile T. rex and Nanotyrannus appear similar in the fossil record, they were two separate species, the new study finds.

Overview

  • Researchers concluded the Montana tyrannosaur was about 20 years old and skeletally mature based on growth rings, vertebral fusion, and developmental anatomy.
  • Fixed anatomical traits—longer forelimbs, higher tooth count, fewer tail vertebrae, and distinct cranial nerve and sinus patterns—conflict with a juvenile T. rex identity.
  • A review of more than 200 tyrannosaur specimens led to recognition of a second species, Nanotyrannus lethaeus, from fossils long labeled as teenage T. rex.
  • The results indicate Tyrannosaurus and Nanotyrannus coexisted in Hell Creek near the end of the Cretaceous, implying greater predator diversity than previously thought.
  • Some experts endorse the stronger case for Nanotyrannus yet caution that distinguishing adult Nanotyrannus from true juvenile T. rex will require additional specimens and reanalysis.