In a significant development, scientists have identified a new species of Tyrannosaurus, distinct from the famous T. rex, based on a partial skull unearthed in 1983 in southeastern New Mexico. The researchers believe that the fossil represents a separate species called Tyrannosaurus mcraeensis, which lived several million years before the T. rex and was of comparable size. This finding challenges the long-standing assumption that T. rex was the sole species of the genus Tyrannosaurus.

The skull, previously identified as a T. rex fossil, showed subtle differences that warranted the recognition of Tyrannosaurus mcraeensis as a distinct species. Paleontologist Nick Longrich of the University of Bath described the lower jaw as shallower and more curved toward the back, and the blunt hornlets above the eyes as lower compared to the T. rex. According to the researchers, these consistent differences imply variations in diet and mate selection compared to the more famous T. rex.

The partial skull, found near the base of Kettle Top Butte, comprises approximately 25% of the entire specimen. Notably, the braincase and upper jaws are missing, limiting the analysis. The study, published in the journal Scientific Reports, suggests that the fossil dates back to 71-73 million years ago.

However, skepticism exists among other researchers who doubt the presence of a new Tyrannosaurus species. They argue that the differences observed in the skull are unremarkable and that the assertion of a 71-73 million-year-old fossil is problematic. Paleontologist Thomas Carr of Carthage College in Wisconsin, who has extensively studied T. rex, called the study "unpersuasive," stating that the features seen in the New Mexico specimen are present in other T. rex fossils.

Nonetheless, the existence of Tyrannosaurus mcraeensis could significantly impact the understanding of Tyrannosaurus evolution. The researchers propose that T. mcraeensis, larger than other closely related Tyrannosaurus species inhabiting northern North America before the T. rex, suggests that giant species within this group evolved millions of years earlier than previously believed, originating from southern North America.

The ongoing debate about additional Tyrannosaurus species has divided the scientific community. In 2022, some researchers put forward the existence of three Tyrannosaurus species based on variations in thighbones and teeth among fossils. However, others disagreed, citing insufficient evidence to support these claims.

While the dispute continues, the discovery of Tyrannosaurus mcraeensis opens up new avenues for paleontologists to unravel the mysteries surrounding the evolution of these fearsome apex predators. Further research and analysis will be necessary to fully understand the implications of this groundbreaking finding and its impact on the field of paleontology.