Throat Bone Evidence Confirms Nanotyrannus as Distinct Tyrannosaur
New research published on December 4, 2025 found that a throat bone from the Nanotyrannus holotype shows growth markers consistent with a mature animal, bolstering the case that Nanotyrannus was a separate species rather than a juvenile Tyrannosaurus rex. The findings force a rethink of predator dynamics in Late Cretaceous western North America and will prompt museums and researchers worldwide to reexamine collections and ecological models.
Scientists released two complementary studies this week that together overturn a decades long consensus that Nanotyrannus represented juvenile individuals of Tyrannosaurus rex. The most recent paper published on December 4 in the journal Science analyzed the hyoid bone, a small throat element, from the Nanotyrannus holotype skull and identified growth ring like markers consistent with an animal approximately 15 to 18 years old. That age places the specimen at or near adult size under conventional tyrannosaur growth trajectories, calling into question the long standing hypothesis that Nanotyrannus was simply an immature T. rex.
An earlier study published in October documented a suite of anatomical differences between Nanotyrannus and T. rex. Those differences include distinct tooth counts, differences in skull crests and air sinuses, and variances in vestigial digits. Taken together the two papers present converging lines of evidence from bone microstructure and comparative anatomy that support the recognition of Nanotyrannus as a separate lineage of large tyrannosaur.
The consensus among many paleontologists since the 1980s favored synonymy with T. rex, in part because juveniles of large theropods can look markedly different from adults. The new hyoid analysis is notable because throat bones are rarely preserved and because growth markers in that element provide an independent test of age that does not rely solely on limb bone histology. By showing that the holotype was not a very young animal, the Science paper weakens the primary argument for synonymy and strengthens the case for taxonomic separation.
If Nanotyrannus is accepted as distinct, the paleontological picture of Late Cretaceous ecosystems in western North America becomes more complex. The idea that two large apex predators coexisted raises questions about how they partitioned prey, habitat and behavior. Ecological models of the time will need revision to account for potential niche differentiation, seasonal resource use, or other mechanisms that allowed two similar sized predators to coexist without driving one lineage to extinction.
The implications extend beyond academia. Museums that display tyrannosaur fossils will face decisions about labeling and interpretation, and collections around the world may be reexamined for overlooked Nanotyrannus material. The debate also highlights the iterative nature of science, as new techniques and rare preserved elements can overturn long held views.
Researchers caution that taxonomic decisions require broad review and that further studies of additional specimens will be needed to solidify Nanotyrannus as a distinct species across its known range. Still, the combination of anatomical differences documented in October and the new hyoid age signal a significant shift in the field. For students of deep time and the public alike, the discovery reshapes a familiar image of the Cretaceous world and opens fresh lines of inquiry into how large predators lived and interacted on ancient landscapes.
