Nanotyrannus Revealed: Fossil Discovery Rewrites Dinosaur History
A groundbreaking new study published Thursday in the journal Nature challenges decades of paleontological research, confirming that a smaller dinosaur previously misidentified as a juvenile Tyrannosaurus rex is, in fact, a distinct species: the adult Nanotyrannus lancensis. This revelation fundamentally alters our understanding of the tyrannosaurid family and the prehistoric ecosystem of North America.
The findings stem from a five-year investigation of a remarkably well-preserved fossil known as “Dueling Dinosaurs,” housed at the North Carolina Museum of Natural Sciences in Raleigh. The fossil depicts two dinosaurs seemingly locked in combat – a Triceratops and what was long believed to be a young T. rex.
“We have the growth record preserved in the microstructure of the bone, which shows it’s an adult,” explained James Napoli, a vertebrate paleontologist at Stony Brook University and co-author of the study. This discovery has significant implications, prompting a reevaluation of numerous fossils previously categorized as adolescent T. rex remains.
While both dinosaurs belonged to the tyrannosaurid family, Nanotyrannus and T. rex were markedly different creatures. Nanotyrannus measured 5.5 meters in length, possessing a lean, agile build optimized for speed, with long legs and powerful arms suited for actively hunting prey. In contrast, the colossal T. rex, reaching 12.8 meters, relied on robust legs and a bone-crushing bite to subdue larger, slower-moving dinosaurs.
Notably, Nanotyrannus boasted proportionally larger forelimbs than the adult T. rex, which is infamous for its diminutive arms. “Bones do not shrink when animals grow, so this could not have become an (adult) T. rex,” Napoli emphasized.
The implications of this research are far-reaching, according to Lindsay Zanno, an associate research professor at North Carolina State University and chief of paleontology at the North Carolina Museum of Natural Sciences. “A large number of studies on T. rex biology over the past three decades have unwittingly mixed data from Nanotyrannus with those from T. rex. Those studies should be reevaluated in light of this discovery,” she stated.
The “Dueling Dinosaurs” fossil was first unearthed in 2006 from the Hell Creek Formation, a rich paleontological site spanning parts of Montana, North Dakota, South Dakota, and Wyoming, and dating back 65.5 million years. Nanotyrannus lancensis was initially identified from a fossil discovered in the 1940s within the same formation. However, subsequent interpretations often reclassified these smaller tyrannosaur fossils as juvenile T. rex, a narrative that persisted for decades despite ongoing debate within the scientific community.
The new research, encompassing an analysis of over 200 tyrannosaur fossils, suggests that juvenile T. rex fossils are less common in the fossil record than previously assumed. For years, researchers mistakenly attributed Nanotyrannus fossils to juvenile T. rex, influencing models of T. rex growth and behavior.
“What’s exciting is that this discovery opens the door to a whole host of new questions about how these different predators—one built for brute strength and another for speed—interacted in the twilight of the dinosaurs,” Zanno added.
Further complicating the picture, the study authors have identified a fossil known as “Jane” as a second species of Nanotyrannus, naming it Nanotyrannus lethaeus. The name references the River Lethe from Greek mythology, symbolizing how this dinosaur remained “forgotten” for decades.
The findings have sparked debate about the speed with which a scientific consensus formed around the idea that all Nanotyrannus specimens were juvenile T. rex. Larry Witmer, a professor of paleontology at Ohio University who was not involved in the study, noted that the commercial collection of many T. rex fossils, often held in private hands, has hindered comprehensive research. “This exceptionally researched study by Zanno and Napoli puts Nanotyrannus on solid footing,” Witmer said. “There is much more at stake here than declaring a winner in the debate, because there are literally decades of research and probably hundreds of publications based on a premise that this article refutes. All of these analyses will need revision.”
Steve Brusatte, a professor of paleontology at the University of Edinburgh, echoed this sentiment, stating that the discovery necessitates “a fundamental reassessment of the classification and evolution of tyrannosaurs.” Brusatte, who was not involved in the new study, admitted that the evidence presented has challenged his own previous assumptions. However, he cautioned that differentiating between adult Nanotyrannus and adolescent T. rex will remain a significant challenge for paleontologists.
Thomas Carr, a senior scientific advisor at the Dinosaur Discovery Museum, agreed that the evidence supporting the Nanotyrannus identification is “pretty conclusive,” but emphasized the need for additional fossils to fully understand the distinctions between Nanotyrannus lancensis and Nanotyrannus lethaeus. He also expressed caution regarding the reclassification of the “Jane” fossil.
The “Dueling Dinosaurs” fossil, still partially encased in rock, promises further insights. Scientists remain uncertain about the circumstances surrounding the dinosaurs’ deaths or why they were found intertwined. However, the remarkably complete Nanotyrannus specimen – with nearly every bone represented, even if partially broken – offers an unprecedented opportunity for research. Researchers hope to uncover preserved skin, feathers, or even evidence of injuries, such as a broken finger.
“There is a tremendous amount of science to be done with dueling dinosaurs,” Napoli concluded. “It’s an incredible fossil to work with.”
