Overview
- A Nature paper identifies the tyrannosaur in the Montana Dueling Dinosaurs pair as Nanotyrannus lancensis rather than a juvenile T. rex.
- Bone growth rings and spinal fusion show the animal was about 20 years old and had stopped growing at roughly half the length and one-tenth the mass of a mature T. rex.
- Fixed anatomical markers—including longer forelimbs, more teeth, fewer tail vertebrae, and distinct cranial nerve foramina—place it outside the T. rex lineage.
- The authors, led by Lindsay Zanno and James Napoli, surveyed more than 200 tyrannosaur fossils and also named a second species, Nanotyrannus lethaeus.
- The reclassification raises estimates of late‑Cretaceous predator diversity and prompts reevaluation of prior T. rex growth and behavior studies, with some researchers calling for additional specimens to further test the conclusions.