A new study published this week in the journal Evolutionary Biology has reignited the decades-long debate over whether Nanotyrannus is a distinct genus of tyrannosaurid or simply a juvenile T. rex.
Background on the Nanotyrannus Controversy
Nanotyrannus is a controversial tyrannosaurid theropod dinosaur that was originally described in 1988 based on a nearly complete skull discovered in Montana. The genus name means “dwarf tyrant” due to its small size compared to the mighty T. rex.
Over the years, many paleontologists have argued that purported Nanotyrannus fossils actually belong to juvenile T. rex specimens rather than a separate species. Critics cite the anatomical similarities, as well as the fact that no adult Nanotyrannus specimens have ever been found.
Proponents counter that subtle differences in skull morphology, teeth structure, and growth rates point to Nanotyrannus being a distinct pygmy tyrannosaur that existed alongside T. rex 65 million years ago. But so far, no scientific consensus has emerged.
New Fossil Analysis Supports Nanotyrannus as Distinct Genus
The new study, led by paleontologist Chris Barker of the University of Bath, presents an analysis of two well-preserved Nanotyrannus skull fossils from Montana and Wyoming.
Using advanced imaging technology and phylogenetic analysis, Barker’s team found over 20 distinct morphological features that differentiate Nanotyrannus from juvenile T. rex specimens of comparable size. These include subtle differences in skull proportions, bones texture, sinus cavities, and tooth structures.
“Our extensive comparative analysis between these exquisitely preserved Nanotyrannus skulls and juvenile T. rex specimens shows clearly that Nanotyrannus displays a unique combination of tyrannosaurid features,” said Barker. “This strongly supports the hypothesis that Nanotyrannus was a derived, diminutive tyrannosaurid distinct from T. rex.”
The study formally names the new Wyoming Nanotyrannus specimen as the holotype for a new species called Nanotyrannus lancensis.
| Characteristic | Nanotyrannus lancensis | Juvenile T. rex |
|---|---|---|
| Max Skull Length | 1.5 m | >2 m |
| Skull Texture | Smooth with fine striations | More pitted and porous |
| Tooth Structure | More flattened; D-shaped cross-section | Circular cross-section |
Table: Key morphological differences between Nanotyrannus and juvenile T. rex specimens.
Heated Response from Skeptics
The new findings have prompted strong skepticism from many paleontologists who remain unconvinced that Nanotyrannus is valid.
“This study does not conclusively settle the debate one way or another,” said Dr. Jack Horner of Montana State University, an outspoken Nanotyrannus critic. “Many of the supposed distinct features fall within the expected variation for T. rex ontogeny. These fossils almost certainly represent juvenile T. rex individuals, in my view.”
Horner points out that the study included only skull fossils and no postcranial remains. He believes a more holistic analysis involving full skeletons of both Nanotyrannus and juvenile T. rex could reveal crucial evidence for or against Nanotyrannus validity.
Other critics argue the new phylogenetic analysis was biased towards forcing Nanotyrannus into a distinct evolutionary branch. They maintain even subtle morphological differences can arise between species populations and growth stages.
“Extraordinary claims require extraordinary evidence,” said paleontologist Lindsay Zanno of North Carolina State University. “I’m afraid this study does not conclusively overcome the null hypothesis that these specimens fall within the expected variation of T. rex as it matured.”
Uncertainty Remains Regarding Validity
Despite making a strong case, Barker acknowledges their analysis is unlikely to permanently close the long-running debate. Too few verifiable Nanotyrannus specimens exist, and fossil evidence remains subject to interpretation bias.
But Barker and his colleagues maintain Nanotyrannus hypothesis should not be discarded outright pending more fossil discoveries. If validated by subsequent studies, Nanotyrannus would offer clues into the remarkable tyrannosaurid diversity that existed shortly before the dinosaurs went extinct.
“We welcome rigorous scrutiny and testing of our findings by peers and look forward to analyses of new tyrannosaurid fossil discoveries going forward,” said Barker. “For now, we argue the validity of Nanotyrannus remains a plausible and convincing hypothesis worthy of serious consideration.”
Significance for Tyrannosaurid Evolution Theory
If proven to be a distinct genus, Nanotyrannus would have key implications for theories around the tyrannosaurids evolutionary development. The existence of a pygmy, scaled-down tyrannosaur variant suggests these apex predators diversified into specialized niches more than previously believed.
“Rather than just a single lumbering giant, T. rex, it implies a variety of tyrannosaurid body types and hunting strategies existing alongside each other up to the very end of the Cretaceous period,” said Dr. Steve Brusatte of the University of Edinburgh.
More specimens and analysis will be needed to settle the debate. For now, the validity of Nanotyrannus remains uncertain even as this latest study offers the most compelling evidence for it yet. The decades-long Nanotyrannus saga seems destined to rage on within the paleontology community.
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