Nanotyrannus Officially Confirmed as Distinct Species – “Bloody Mary” and Dueling Dinosaurs End Decades-Long T. rex Debate

In a 2025 scientific bombshell published in Science, paleontologists Lindsay Zanno and James Napoli have definitively proven that Nanotyrannus is a valid genus — not a juvenile Tyrannosaurus rex. The landmark study, based on the spectacular “Bloody Mary” specimen from the Dueling Dinosaurs fossil, ends one of paleontology’s longest-running controversies.

The nearly complete skeleton (NCSM 40000), part of the famous Dueling Dinosaurs pair acquired by the North Carolina Museum of Natural Sciences, belongs to a skeletally mature adult Nanotyrannus lancensis. Histological analysis shows fused growth plates and no evidence of the rapid juvenile growth spurt characteristic of T. rex. Key anatomical differences include more teeth (up to 74 vs. ~60 in adult T. rex), distinct snout nerve patterns, proportionally longer legs, stronger arms with a vestigial third finger, and a more gracile build suited for speed rather than brute force.

The study also names a second species, Nanotyrannus lethaeus, based on the “Jane” specimen, highlighting greater diversity among small tyrannosauroids in the Hell Creek Formation. Nanotyrannus lived alongside T. rex in the final days of the Cretaceous, occupying a different predatory niche as a swift, agile hunter.

Zanno called the Dueling Dinosaurs specimen “the smoking gun that finally settles the debate.” With Nanotyrannus now recognized as a separate lineage, scientists must rethink Late Cretaceous food webs and tyrannosauroid evolution.

The fossils are on public display at the North Carolina Museum of Natural Sciences, where “Bloody Mary” continues to captivate visitors — living proof that even the most famous dinosaurs still hold surprises.