Nanotyrannus Officially Revived as Distinct Species from T. rex After “Bloody Mary” Analysis in Montana!

Paleontologists have delivered the final blow to the long-standing “Nanotyrannus is just a baby T. rex” hypothesis with the detailed study of “Bloody Mary,” a spectacular new tyrannosaur specimen from Montana’s Hell Creek Formation.

Described in a October 2025 Nature paper by Lindsay Zanno and James Napoli, “Bloody Mary” (NMMNH P-25000) is a near-complete adult skeleton of Nanotyrannus lancensis that died at approximately 6–7 meters long — far smaller than even subadult T. rex. High-resolution CT scans and bone histology reveal fully fused neurocentral sutures and dense growth rings indicating skeletal maturity at death, not the rapid juvenile growth pattern of Tyrannosaurus.

The specimen shows dozens of anatomical differences from T. rex, including a more gracile skull, proportionally longer arms with three functional fingers, a differently shaped braincase, and unique vertebral laminae. These traits are consistent across multiple Nanotyrannus specimens and cannot be explained by ontogeny.

“This is the smoking gun,” Zanno states. “Bloody Mary proves Nanotyrannus was a fully grown, distinct predator that lived alongside T. rex in the same ecosystem.” The name “Bloody Mary” was given by the field team after the vivid red hemaтιтe staining that preserved the bones in exquisite detail.

The confirmation dramatically increases late-Cretaceous predator diversity in North America and forces a complete re-evaluation of every growth study that previously lumped Nanotyrannus specimens into T. rex ontogeny curves. As more Hell Creek material is re-examined, the “small king” has officially reclaimed its throne as a separate species.