Meet Tyrannosaurus mcraeensis, the oldest and most primitive cousin of T. rex

A new subspecies of tyrannosaur has been identified from a partial skull found in New Mexico, shedding light on the origins of the iconic T. rex in North America.

The new subspecies, named Tyrannosaurus mcraeensis, is the oldest and most primitive known relative of T. rex on the continent. It lived about 73 million years ago, predating T. rex by up to 7 million years. It was roughly the same size as T. rex, reaching about 12 meters (40 feet) in length and weighing 10 tons. It also had similar proportions, with a large head, powerful jaws, and tiny arms.

However, there were some subtle differences between the two subspecies, such as the shape and size of the teeth and the curvature of the jaw. These differences suggest that Tyrannosaurus mcraeensis was not a direct ancestor of T. rex, but rather a side-branch in the tyrannosaur family tree.

Meet Tyrannosaurus mcraeensis, the oldest and most primitive cousin of T. rex
Meet Tyrannosaurus mcraeensis, the oldest and most primitive cousin of T. rex

A breakthrough discovery in New Mexico

The fossil evidence for Tyrannosaurus mcraeensis was first discovered in the 1980s by boaters on the shore of New Mexico’s largest reservoir. The partial skull was displayed at the New Mexico Museum of Natural History and Science (NMMNHS), but its true identity remained unknown until a team of researchers from several universities and institutions reexamined it in detail.

The researchers compared the skull with numerous specimens of T. rex and other tyrannosaurs, and found that it belonged to a new subspecies that had not been recognized before. They published their findings in the journal Scientific Reports on Thursday, January 11, 2024.

The new subspecies was named after the McRae family, who own the land where the fossil was found, and who have been supportive of the scientific research.

A new perspective on the evolution of tyrannosaurs

The discovery of Tyrannosaurus mcraeensis has important implications for understanding the evolution of tyrannosaurs in North America. Previously, it was unclear how T. rex, the largest and most fearsome land predator in history, appeared on the continent about 66 million years ago, without any close relatives.

The new subspecies shows that tyrannosaurs were in North America much longer than previously thought, and that they diversified into different forms over time. It also suggests that there may be more undiscovered tyrannosaur species waiting to be found in the region.

“New Mexicans have always known our state is special, now we know that New Mexico has been a special place for tens of millions of years,” said Dr. Anthony Fiorillo, Executive Director of NMMNHS and a co-author of the study. “This study delivers on the mission of this museum through the science-based investigation of the history of life on our planet.”

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