New Research Confirms Existence of Smaller Tyrannosaur Species

Paleontologists have identified a new species of small tyrannosaur, resolving a long-standing debate over whether certain fossils belonged to a juvenile Tyrannosaurus rex or a distinct, smaller species. Research conducted by scientists at North Carolina State University and Ohio University concluded that the diminutive predator, named Nanotyrannus lancensis, existed alongside its larger relative during the late Cretaceous period.

The study, published on October 30, 2023, in the journal Nature, highlights the significance of a small skull discovered in 1946 at Montana’s fossil-rich Hell Creek Formation. Initially classified as a species of Gorgosaurus, the skull later sparked controversy as some paleontologists argued it belonged to a juvenile T. rex. This debate centered on whether Nanotyrannus represented a unique species or merely an immature form of T. rex.

Unraveling the Controversy

Paleontologists Lindsay Zanno and Lawrence Witmer emphasized that the discussion surrounding Nanotyrannus has been contentious, with passionate arguments from both sides. Their recent expedition to the Hell Creek Formation yielded a well-preserved, nearly complete skeletal specimen of a tyrannosauroid. This new find, along with the 1946 skull, supports the existence of Nanotyrannus as a separate species.

The crucial evidence came from an analysis of the new specimen’s skeletal structure, which indicated it was nearly fully grown. If it were a juvenile, its bones would still show signs of development. Further modeling suggested that Nanotyrannus demonstrated different growth patterns compared to T. rex, reinforcing the argument for its classification as a distinct genus.

The researchers determined that the Nanotyrannus genus includes at least two species: Nanotyrannus lancensis and Nanotyrannus lethaeus. This revelation challenges the previously accepted notion that T. rex was the sole tyrannosauroid in North America during the late Cretaceous.

Characteristics of Nanotyrannus

In contrast to the imposing T. rex, which could exceed 42 feet in length and weigh over nine tons, adult Nanotyrannus reached a maximum length of approximately 18 feet and weighed around 1,550 pounds. While T. rex evolved for brute strength with its robust legs and powerful bite, Nanotyrannus adapted a more agile physique. Its longer legs and strong arms enabled it to ambush prey quickly, showcasing a different hunting strategy.

The confirmation of Nanotyrannus suggests that Tyrannosaurus likely coexisted with at least one smaller relative for about one million years leading up to the Cretaceous-Paleogene extinction event. This challenges the previously held belief that dinosaur diversity was already in decline before this catastrophic event.

The authors of the study stated, “Our results undermine a nearly uniform consensus among theropod specialists and rectify a significant taxonomic error underpinning decades of research.” They added that the implications of this research extend far beyond the identification of a new species, potentially reshaping the understanding of tyrannosauroid evolution.

As paleontology continues to unveil the complexities of ancient ecosystems, the discovery of Nanotyrannus highlights the intricate relationships that existed among prehistoric predators. This research not only enriches the narrative of dinosaur history but also enhances our understanding of the biodiversity that thrived in North America during the late Cretaceous period.