For decades, paleontologists have debated whether the meat-eating dinosaur Nanotyrannus was actually just a juvenile Tyrannosaurus. But in a span of five weeks, the question appears to have been definitively resolved by two new studies that show that Nanotyrannus was clearly distinct from T. rex.
The most recent study, published Thursday, focused on a throat bone called the hyoid from the first Nanotyrannus fossil ever discovered — a skull unearthed in Montana in 1942. The researchers detected a record of growth on the hyoid, similar to the annual growth rings of a tree, showing that this individual was between 15 and 18 years old, and therefore fully grown or nearly so.
The discovery follows a study published on October 30 by different researchers who used other bones to establish a growth record and identified anatomical differences in the fossils of Nanotyrannus and Tyrannosaurus, also contradicting the notion that they were the same dinosaur.
The hyoid was part of a skull fossil that was the “holotype” (official reference for the description of a species) specimen of Nanotyrannus, stored at the Cleveland Museum of Natural History.
“The main discovery is that the holotype specimen of Nanotyrannus lanceensisthe fossil that formally defines the species, represents a mature individual and therefore cannot belong to an immature Tyrannosaurus rex, as has often been interpreted in the past. Instead, it shows that Nanotyrannus is a distinct species of carnivorous dinosaur that lived alongside T. rex,” said Princeton University paleontologist Christopher Griffin, lead author of the research published in the journal Science.
“The fact that these two studies were published so close to each other really seems like a double whammy for Nanotyrannus,” said Cleveland Museum of Natural History paleontologist and senior author of the study Caitlin Colleary.
Studies show that two large predators prowled western North America in the twilight of the age of dinosaurs during the Cretaceous period, which ended 66 million years ago when one struck Earth. Tyrannosaurus is the largest known carnivorous dinosaur. Nanotyrannus, about a tenth the mass of , was nevertheless a fierce and agile hunter.
