The fossil, named Tyrannosaurus mcraeensis, predates the renowned T-rex

Scientists reevaluating a partial skull unearthed in 1983 in southeastern New Mexico have identified it as a new species of Tyrannosaurus, challenging the long-standing dominance of T-rex in the genus.

The fossil, named Tyrannosaurus mcraeensis, predates the renowned T-rex, living several million years before and exhibiting subtle yet significant differences.

Previously thought to be a T-rex, the skull’s unique features, including a shallower and more curved lower jaw and lower blunt hornlets above the eyes, set it apart from known T-rex specimens.

Researchers, led by palaeontologist Anthony Fiorillo, Executive Director of the New Mexico Museum of Natural History & Science, assert that these differences are consistent and imply variations in diet and mate selection compared to the more famous T-rex.

The jaw of the newly identified dinosaur species Tyrannosaurus mcraeensis in lateral (top) and medial (bottom) views, from a fossil at the New Mexico Museum of Natural History & Science in Albuquerque, New Mexico, US. —Reuters
 The jaw of the newly identified dinosaur species Tyrannosaurus mcraeensis in lateral (top) and medial (bottom) views, from a fossil at the New Mexico Museum of Natural History & Science in Albuquerque, New Mexico, US. —Reuters

Despite scepticism from some researchers who find the distinctions unremarkable, the team maintains that the subtle variations are key and contribute to a broader understanding of Tyrannosaurus evolution. Fiorillo emphasised the importance of the feature above the eyes, suggesting implications for sexual selection.

The discovery challenges the traditional narrative of T-rex as the sole species within the genus Tyrannosaurus, which has stood since its first description in 1905.

T. mcraeensis, with approximately 25% of the skull collected to date, sheds light on the early evolution of giant Tyrannosaurus species, indicating their existence in southern North America millions of years before the T-rex.

A view of teeth of the newly identified dinosaur species Tyrannosaurus mcraeensis, from a fossil at the New Mexico Museum of Natural History & Science in Albuquerque, New Mexico, US. —Reuters
 A view of teeth of the newly identified dinosaur species Tyrannosaurus mcraeensis, from a fossil at the New Mexico Museum of Natural History & Science in Albuquerque, New Mexico, US. —Reuters

Notably, the dating of the fossil, estimated at 71-73 million years ago, is contentious, with some experts questioning the methodology.

Paleontologist Thomas Carr expressed scepticism, deeming the study “unpersuasive” and citing the lack of discrete and obvious differences.

The fossil’s age, determined by the rock beneath it, is disputed, as existing evidence suggests T-rex appeared no earlier than 67 to 68 million years ago.

The debate surrounding potential additional Tyrannosaurus species has been ongoing, with this recent discovery adding a new dimension to our understanding of these iconic dinosaurs.

The emergence of Tyrannosaurus mcraeensis challenges preconceptions, highlighting the complexity of dinosaur evolution and the need for continued exploration and scrutiny within palaeontology.

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