Nanotyrannus probably was a small adult dinosaur, not a teenage T. rex

Following a groundbreaking study in October that recognized Nanotyrannus as a distinct dinosaur, a new team of paleontologists independently confirmed the finding: this small predator was an adult of its own species, rather than a teenage Tyrannosaurus rex. The latest research, published Thursday in Science, analyzed a tiny throat bone from the original specimen that sparked decades of debate.

By examining microscopic details of the hyoids ceratobranchiala part of the throat that changes with ageand comparing it to similar bones in ostriches, alligators, T. rex, and Allosaurus, researchers could determine the dinosaur's maturity. Their findings showed that the fossil belonged to a fully grown individual, not a juvenile.

Caitlin Colleary, a paleontologist at the Cleveland Museum of Natural History and co-author of the study, described the results as surprising. Most experts believed the skull belonged to a young T. rex, she said, so I expected our research to support that view.

Discovered in 1942 in Montanas Hell Creek Formation, the Cleveland skull was first named Gorgosaurus lancensis due to its resemblance to Gorgosaurus. Later research suggested it might represent a juvenile T. rex, but a 1988 study proposed it was a small tyrannosaur of its own genus, leading to the name Nanotyrannus lancensis.

Over forty years, debate over the dinosaurs classification continued. Recent studies, however, have provided strong evidence confirming Nanotyrannus as a valid species. James Napoli, who co-authored the October study, remarked, This research shows that the Nanotyrannus specimen was nearly fully grown at death and could not be a juvenile T. rex.

Adult T. rex individuals were roughly three times the length of Nanotyrannus and weighed significantly more. The findings also suggest that Nanotyrannus lived alongside T. rex in Late Cretaceous forests and floodplains, potentially competing for prey.

Insights from Dinosaur Throat Bones

In 2021, Christopher Griffin of Princeton University began investigating whether throat bones in birds, crocodiles, and dinosaurs could reveal growth patterns. Simultaneously, Colleary started work at the Cleveland Museum of Natural History and noticed the ceratobranchial bone from the Nanotyrannus skull. This bone became a key piece for analyzing dinosaur maturity.

Comparisons between the Nanotyrannus bone and that of a teenage T. rex showed more numerous and closely spaced growth rings in Nanotyrannus, indicating skeletal maturity. Parts of the Cleveland specimens throat bone had healed injuries, but other sections clearly showed compact, remodeled tissue characteristic of adult dinosaurs.

Colleary and colleagues identified an external fundamental system (EFS) in the bone tissue, typically signaling that growth has stopped, confirming the dinosaur was fully grown at death.

Some caution remains. Jared Voris of the University of Calgary noted that the EFS could be confused with other growth rings, meaning the dinosaur might still have been growing. Further studies on Nanotyrannus specimens, including the dueling dinosaurs referenced in Napolis paper, will refine these findings.

Despite this, renewed evidence for Nanotyrannus represents a notable shift in paleontology. Colleary emphasized that collaboration enhances scientific understanding, and having multiple studies on the Cleveland skull strengthens the case for Nanotyrannus as a distinct adult dinosaur.

Author: Ethan Caldwell