A significant breakthrough in paleontology has confirmed that the dinosaur known as Nanotyrannus lancensis is a distinct species rather than a juvenile Tyrannosaurus rex. This revelation, published on October 30 in the journal Nature, stems from an analysis of a well-preserved skeleton found in Montana’s Hell Creek Formation, which dates back approximately 67 million years.
The fossil, part of the renowned Dueling Dinosaurs specimen, showcases a small tyrannosaur entangled with a horned ceratopsian dinosaur. This discovery serves as a crucial link for researchers who have long sought to demonstrate the validity of Nanotyrannus as a separate entity from its more famous counterpart, T. rex. The analysis indicates that this skeleton represents the first identified adult specimen of Nanotyrannus, allowing scientists to finally separate it from T. rex.
The identity of Nanotyrannus has been debated for decades. Originally unearthed in 1942, the skull of this small dinosaur was initially classified as Gorgosaurus. However, in 1988, paleontologists redefined it as a new species, Nanotyrannus lancensis. Despite this classification, many scientists argued that the features of the skull closely resembled those of a juvenile T. rex.
Recent findings led by paleontologists Lindsay Zanno from North Carolina State University and James Napoli from Stony Brook University indicate that the newly analyzed fossil is not just a young dinosaur but a fully grown adult specimen, measuring around six meters in length. Analysis of growth rings in its leg and arm bones confirms its skeletal maturity. In contrast, adult T. rex specimens can reach lengths of up to 14 meters.
The new fossil provides the first preserved tail and arm bones of Nanotyrannus, which exhibit distinct differences from T. rex. For instance, while a T. rex tail comprises roughly 40 vertebrae, N. lancensis contains only 35. Furthermore, Zanno notes that the arms of Nanotyrannus are proportionally larger than those of T. rex, marking a significant anatomical divergence.
In addition to confirming the identity of Nanotyrannus, the study reevaluates another well-known specimen, referred to as Jane. Previously thought to be a juvenile of T. rex, the new analysis suggests that Jane is, in fact, a young Nanotyrannus and proposes a new species, N. lethaeus, named after the River Lethe from Greek mythology, symbolizing the idea that Jane has been overlooked for decades.
The findings have been met with some skepticism. Holly Ballard, a paleontologist at Oklahoma State University, acknowledges the analysis’s conclusions regarding the Dueling Dinosaur specimen’s size but questions the classification of Jane as a new species. She notes that Jane was already larger than N. lancensis and was still in a growth phase.
Both Zanno and Holtz emphasize that Nanotyrannus and T. rex might have coexisted in the Hell Creek region, each occupying different ecological niches. Zanno describes Nanotyrannus as a smaller, more agile predator, contrasting with the bulkier and more powerful T. rex. This diversity underscores that dinosaurs were flourishing and exhibiting a wide range of adaptations right up to the end of the Cretaceous Period 66 million years ago.
The implications of this study extend beyond the validation of Nanotyrannus as a legitimate species. It calls into question decades of research pertaining to T. rex, as much of the data may have previously conflated two distinct species. Zanno stresses the importance of reevaluating existing research on locomotion, diet, and growth patterns of T. rex in light of these revelations.
Looking ahead, both scientists express anticipation for a particular fossil currently being prepared at the Denver Museum of Nature & Science, which is believed to be an authentic juvenile T. rex. This could provide additional insights into the anatomical differences between the two species, further enriching our understanding of these iconic dinosaurs.
