Overview
- The Hell Creek tyrannosaur entombed with a Triceratops is identified as Nanotyrannus lancensis rather than a juvenile Tyrannosaurus rex.
- Fixed anatomical differences from T. rex include a higher tooth count, proportionally longer forelimbs, fewer tail vertebrae, and distinct cranial nerve and sinus patterns.
- After examining more than 200 tyrannosaur fossils, the authors also name a second species, Nanotyrannus lethaeus, proposing that the well‑known “Jane” specimen belongs to this taxon.
- The findings call for a re‑evaluation of decades of T. rex research that relied on small specimens now reassigned, and they indicate multiple tyrannosaur predators coexisted in late Cretaceous ecosystems.
- Several experts welcome the evidence for Nanotyrannus yet urge caution on broader claims, with forthcoming material such as a potential teen T. rex in Denver expected to further test the conclusions.