Overview
- The tyrannosaur from the Dueling Dinosaurs fossil is identified as an adult Nanotyrannus lancensis, about 20 years old, based on growth rings, spinal fusion and developmental anatomy.
- Researchers compared more than 200 tyrannosaur fossils and designate a second species, Nanotyrannus lethaeus, reclassifying the debated “Jane” specimen.
- Nanotyrannus shows fixed differences from T. rex, including more teeth, distinct cranial nerve and sinus patterns, larger forelimbs with a vestigial third finger, and fewer tail vertebrae.
- Estimated adult size is roughly 18 feet and 1,500 pounds—about one-tenth the mass of T. rex—indicating multiple tyrannosaur predators coexisted late in the Cretaceous.
- The findings mean studies using Nanotyrannus as a stand-in for teenage T. rex need review, while some experts urge further work to sort small tyrannosaur specimens and pinpoint true juvenile T. rex fossils.