New Study Confirms Nanotyrannus as Distinct Species from T. rex

Paleontologists have reached a significant conclusion regarding the classification of the “dwarf” tyrannosaur, Nanotyrannus lancensis. A study published in the journal Science asserts that this species, which existed alongside Tyrannosaurus rex, is not merely a juvenile version of T. rex but a distinct species in its own right. This finding aligns with a previous study in Nature that also advocated for the recognition of Nanotyrannus as a separate species.

The question of whether different dinosaur specimens represent various growth stages of the same species has been a longstanding debate in paleontology. Christopher Griffin, the first author of the study and a curatorial affiliate at the Yale Peabody Museum, highlighted the challenge as a persistent issue within the field. He stated, “This finding gives us a new way to gauge maturity in individuals lacking limb bones. We think it can be broadly applicable to similar problems throughout the dinosaurian fossil record.”

Determining the maturity of a dinosaur typically involves studying growth rings in limb bones, akin to counting tree rings in trees. However, the holotype of Nanotyrannus, the specimen that defines the species, only includes an isolated skull without any limbs. To overcome this limitation, Griffin and his team focused on the throat bones, known as hyoids, which can also indicate maturity.

To validate their approach, the researchers examined hyoid bones from modern relatives of dinosaurs, such as birds and crocodiles, as well as fossil specimens like Allosaurus. Their analysis of the hyoid from Nanotyrannus revealed all the characteristics indicative of a fully mature individual, reinforcing the classification of this creature as a distinct species.

“This is the first direct determination of maturity for the holotype specimen, the specimen that holds the name Nanotyrannus lancensis and defines the species,” Griffin remarked. He emphasized that while previous research on other specimens identified as Nanotyrannus had been valuable, this new study confirms that the holotype itself represents a mature individual.

The research was largely conducted at Yale, with many analyses performed on the hyoid at the Peabody Museum. The museum’s extensive collections provided essential samples, including hyoids, limb bones, and ribs from crocodilians and birds, along with an Allosaurus specimen collected by the renowned paleontologist Othniel Charles Marsh in the 1800s. Griffin noted, “The Peabody collections were a crucial piece in showing that this new method was viable.”

This new insight into Nanotyrannus raises important questions regarding the growth and development of Tyrannosaurus, as much of the previous information had been based on assumptions about Nanotyrannus. The findings suggest a greater diversity among carnivorous dinosaurs, hinting at more complex ecological interactions during the late Cretaceous period in North America.

Funding for this significant study was provided through a National Science Foundation Postdoctoral Research Fellowship, underscoring the value of continued research in understanding the complexities of dinosaur evolution.