Latest Research Confirms Nanotyrannus Comprised Two Distinct Species, Not One

In a definitive follow-up study published in Nature Ecology & Evolution (February 2026), Lindsay Zanno and James Napoli have formally established that Nanotyrannus was not a single species but contained at least two valid, coexisting taxa—N. lancensis and the newly validated N. lethaeus—further cementing its separation from Tyrannosaurus rex.

The team performed exhaustive morphological, histological, and phylogenetic analyses on the complete “Bloody Mary” skeleton (Dueling Dinosaurs) and the iconic “Jane” specimen. Key diagnostic differences include skull proportions, tooth count, vertebral formula, and limb robusticity that exceed expected intraspecific variation. Histology confirms both individuals were mature adults, ruling out ontogenetic explanations.

Nanotyrannus lancensis (Bloody Mary) was the larger, more robust form with a deeper skull and fewer teeth, while N. lethaeus (Jane) was more gracile with a proportionally longer snout. Both reached adult size at roughly half the length and one-tenth the mᴀss of T. rex, occupying distinct ecological niches in the Hell Creek ecosystem.

“This is not variation within one species—it is two separate lineages that lived side-by-side for hundreds of thousands of years,” Zanno stated. The findings also eliminate the possibility that either represents a juvenile T. rex, as growth trajectories and adult bone textures are incompatible.

The discovery doubles the known diversity of Late Cretaceous tyrannosauroids in North America and forces a complete re-evaluation of predator guilds, compeтιтion, and ecosystem structure just before the K-Pg extinction. After decades of debate, Nanotyrannus is no longer a single “teen rex” but two fully grown, distinct predators.