The partial cranium of a dinosaur discovered 40 years in the past has now been recognized as a brand new species of Tyrannosaurus, and maybe the closest relative of Tyrannosaurus rex. The analysis provides a brand new twist to a long-running debate about what number of species of tyrannosaurs there have been, and will assist to make clear how the long-lasting predator advanced.

T. rex appeared in North America round 68 million years in the past, 2 million years earlier than the mass extinction that worn out most dinosaurs. Palaeontologists have been stumped as to the carnivore’s origins. Some have steered that the ancestors of T. rex walked over a land bridge from prehistoric Asia, whereas others positioned its origins in southern North America.

Anthony Fiorillo on the New Mexico Museum of Pure Historical past and Science and his colleagues re-examined a fossil within the museum’s assortment, which was present in rock layers referred to as the McRae Group in western New Mexico.

Whereas the cranium had initially been categorised as T. rex, Fiorillo and his colleagues seen variations with the bones. They suggest that the specimen represents an older species, which they named Tyrannosaurus mcraeensis in reference to the rocks wherein it was discovered.

They estimate that the dinosaur was about 12 metres lengthy, comparable in measurement to T. rex, nevertheless it lived about 4 million years earlier.

The variations between T. rex and T. mcraeensis would have been comparatively refined. Whereas T. rex had distinguished ridges on its brows and broad, bone-crushing jaws, the identical ridges on T. mcraeensis had been much less effectively developed and its cranium is extra slender, says Fiorillo.

Different current research have proposed that there have been a number of species of Tyrannosaurus and that some so-called T. rex fossils must be reassigned. Such proposals have been controversial, nonetheless, and largely dismissed by dinosaur palaeontologists. The brand new examine will gas additional debate over what number of Tyrannosaurus species there have been in North America.

“I hesitate to treat Tyrannosaurus mcraeensis as being distinct from Tyrannosaurus rex,” says Jared Voris on the College of Calgary in Canada. He notes that lots of the anatomical options that supposedly make the brand new species distinctive can be present in specimens of T. rex.

Whatever the species task, the existence of such a big tyrannosaur a number of million years earlier than T. rex hints that south-western North America was an essential centre for the dinosaur’s evolution. “The proposed age dates for the specimen are peculiar and really a lot warrant extra examine,” says Voris, as they may define a clearer image of dinosaur evolution in the previous couple of million years of the Cretaceous Interval.

The New Mexico tyrannosaur was present in the identical rocks as large horned dinosaurs, duckbilled dinosaurs and long-necked herbivores that would attain 30 metres in size. Fiorillo and his colleagues counsel the lineage resulting in T. rex may need advanced their large measurement to prey on these giant herbivores, later spreading northward because the final of the “tyrant lizards” to stalk the planet.