Confirmation: Nanotyrannus was a separate species, not a young T. rex

After decades of debate, paleontologists now have strong evidence that the meat-eating dinosaur Nanotyrannus was not a juvenile Tyrannosaurus rex. Two recent studies, released within five weeks of each other, demonstrate that Nanotyrannus was a distinct species.

The latest research examined a throat bone called the hyoid from the first Nanotyrannus skull discovered in Montana in 1942. Analysis of growth patterns in this bone, similar to tree rings, indicated that the dinosaur was between 15 and 18 years oldessentially an adult or nearly fully grown.

This follows an October study that analyzed other skeletal bones and found anatomical differences between Nanotyrannus and T. rex, further confirming they were not the same dinosaur. The hyoid came from the holotype specimen, the fossil defining the species, which is preserved at the Cleveland Museum of Natural History.

Christopher Griffin, a Princeton University paleontologist and lead author of the new study published in Science, explained that the holotype represents a mature individual, meaning it cannot be a juvenile T. rex. The evidence shows that Nanotyrannus lived alongside T. rex as a separate predatory species.

Since the skull's discovery eight decades ago, scientists have debated its identity. The controversy intensified in 1988 when Nanotyrannus was formally named as a separate genus.

Caitlin Colleary, senior author from the Cleveland Museum of Natural History, described the timing of the two studies as a "one-two punch" for confirming Nanotyrannus as a distinct species. The findings suggest that two large predators coexisted in western North America at the end of the Cretaceous period, around 66 million years ago.

While Tyrannosaurus was the largest meat-eating dinosaur, Nanotyrannus was smallerabout 5 meters (16.4 feet) long and weighing roughly 700 kg (1,543 pounds), comparable to a modern polar bear. Despite its smaller size, it was fast, agile, and a formidable hunter.

The two species had different body structures. Nanotyrannus had long legs, a long snout with blade-like teeth, and strong arms for handling prey. In contrast, Tyrannosaurus was built for power, with a massive head, thick banana-shaped teeth, stocky legs, and small arms. Additional differences included more teeth in Nanotyrannus, a small crest above the eyes, a distinct air sinus in the skull, and a vestigial third fingerfeatures not present in T. rex.

The study of the hyoid represents the first time this bone has been used to determine dinosaur growth. Unlike limb bones, no limb bones were available from the holotype. The hyoid supports the tongue and is involved in swallowing and breathing. In humans, it is horseshoe-shaped, while in Nanotyrannus, it is tubular.

Researchers also examined hyoids from several T. rex specimens, including large subadults and juveniles. Their findings indicate that juvenile T. rex shared the environment with fully grown Nanotyrannus, implying competition between these predators.

Zachary Morris of the Natural History Museum of Los Angeles County noted that future studies could further illuminate how these two predators coexisted. Smaller animals at the time faced multiple large predators, making survival particularly challenging.

Author: Noah Whitman