The ongoing debate in the field of palaeontology regarding a dinosaur fossil that was originally thought to be a juvenile Tyrannosaurus rex has finally been settled. Researchers have discovered that the fossil actually belongs to a fully grown carnivore of a different species, known as Nanotyrannus.
The skull, initially found in Montana’s Hell Creek Formation in the 1940s, was first classified as a Gorgosaurus before being suggested to be a juvenile T. rex. In 1988, researchers argued that the fossil belonged to an adult of a smaller, related species, which they named Nanotyrannus lancensis. Since then, additional fossils identified as Nanotyrannus have sparked a debate among palaeontologists, with many believing these specimens to be juvenile T. rex individuals.
However, a recent analysis of a complete skeleton from a fossil specimen known as the “Duelling Dinosaurs” has provided conclusive evidence that Nanotyrannus is indeed a separate species. This skeleton, part of a pair discovered in 2006, features a Triceratops buried alongside what was originally thought to be a juvenile T. rex.
Upon thorough examination of the fossil, researchers Lindsay Zanno and James Napoli have identified distinct anatomical features in Nanotyrannus, including different nerve and sinus patterns in the skull, more teeth, large hands, and a shorter tail. These traits remain consistent across the skeleton, confirming that Nanotyrannus is a unique species.
Further analysis of limb bones revealed that the Nanotyrannus specimen was a fully grown individual weighing around 700 kilograms and measuring approximately 5.5 meters in length. This size is significantly smaller than a fully grown Tyrannosaurus rex, highlighting the differences between the two species.
Additionally, Zanno and Napoli reanalyzed 200 tyrannosaur fossils and determined that another specimen from the Hell Creek Formation, known as Jane, previously thought to be a teenage T. rex, is actually a new species within the Nanotyrannus genus, named Nanotyrannus lethaeus.
The resolution of the Nanotyrannus debate has been met with approval from experts in the field, with Scott Persons describing Nanotyrannus as one of the most formidable dinosaur predators. The unique characteristics of Nanotyrannus, compared to T. rex, suggest different hunting strategies, similar to modern cheetahs and lions.
While the identification of Nanotyrannus as a distinct species has been widely accepted, debates continue regarding the classification of other fossils, such as Jane. Nevertheless, this groundbreaking research sheds light on the diversity of tyrannosaur species and their evolutionary history.
