New Analysis Reveals Nanotyrannus as Distinct Dinosaur Species
Paleontologists have confirmed that the small theropod dinosaur previously thought to be a juvenile Tyrannosaurus rex is, in fact, a distinct species known as Nanotyrannus lancensis. The findings, published on October 30, 2023, in the journal Nature, provide clarity on a long-standing debate in the field of paleontology.
The analysis centers around a well-preserved skeleton from Montana’s Hell Creek Formation, estimated to be around 67 million years old. This specimen is part of the famous fossil known as the Dueling Dinosaurs, which features a small tyrannosaur intertwined with a ceratopsian dinosaur. Researchers assert that this fossil represents the first identified adult specimen of Nanotyrannus, allowing them to separate it definitively from T. rex.
The identity of Nanotyrannus has been a subject of dispute since its discovery. Initially unearthed in 1942, the skull of a small dinosaur was believed to belong to Gorgosaurus. In 1988, researchers reclassified it as a new species, Nanotyrannus lancensis. However, many scientists argued that its features closely resembled those of a juvenile T. rex. For decades, several small tyrannosaur fossils unearthed in the same region were assumed to be young versions of the iconic predator.
Paleontologists Lindsay Zanno of North Carolina State University and James Napoli of Stony Brook University led the latest research, revealing critical growth characteristics of the Dueling Dinosaurs specimen. At approximately six meters long, it exhibited signs of being skeletally mature, indicating it was fully grown. Adult T. rex, by contrast, can reach lengths of up to 14 meters.
The new analysis highlights specific differences between the two species, particularly in their skeletal structures. For instance, the tail of N. lancensis contained 35 vertebrae, compared to the 40 vertebrae found in a T. rex tail. Furthermore, the arm bones of N. lancensis were distinctly larger than those of T. rex, suggesting different predatory adaptations.
Both Zanno and her team examined another notable fossil, known as Jane, previously interpreted as a juvenile. Through comparison with the Dueling Dinosaurs fossil and over 100 other tyrannosaur specimens, they concluded that Jane represented a young N. lancensis, potentially a new species named N. lethaeus. This name references the River Lethe from Greek mythology, symbolizing the idea that Jane’s identity had been overlooked for years.
Despite the compelling nature of these findings, some experts remain cautious. Holly Ballard, a paleontologist at Oklahoma State University, acknowledged the Dueling Dinosaur specimen’s adult status but expressed skepticism regarding Jane’s classification as a new species of Nanotyrannus. She noted that Jane was larger than N. lancensis and still growing, complicating the narrative surrounding these dinosaurs.
The research indicates that Nanotyrannus and T. rex could have coexisted in the Hell Creek region, each occupying different ecological niches. Zanno described Nanotyrannus as a “small, slender, extremely fast” predator, in contrast to the bulky and powerful T. rex. This discovery underlines the diversity of dinosaurs leading up to the end of the Cretaceous Period, approximately 66 million years ago.
According to Thomas Holtz, a paleontologist at the University of Maryland, the findings enhance our understanding of the ecological dynamics in the Hell Creek area. He emphasized that the new evidence strengthens the case for the existence of multiple tyrannosaur species in a single community, making the Hell Creek Formation less anomalous.
The implications of this research extend beyond the identification of a new species. Zanno remarked that it challenges decades of research on T. rex, necessitating a reevaluation of existing data concerning its locomotion, diet, and growth patterns. The discovery of Nanotyrannus raises further questions about what a juvenile T. rex might have looked like.
Looking ahead, both Zanno and Holtz hinted at an exciting prospect. A fossil currently being prepared at the Denver Museum of Nature & Science may represent a true juvenile T. rex, offering further insights into the anatomical differences that have sparked debate among researchers for generations.
