A massive tyrannosaurid dinosaur likely roamed the floodplains of present-day New Mexico around 74 million years ago, as revealed by a team of paleontologists from Bath University, Montana State University, and the New Mexico Museum of Natural History and Science.

Bistahieversor sealeyi hunting Pentaceratops sternbergi. Image credit: A. Belov / CC BY 3.0.

“Tyrannosaurids were among the largest and latest predatory dinosaurs,” stated lead author Dr. Nicholas Longrich from the University of Bath and his collaborators in their research paper.

“Following the extinction of carcharodontosaurs during the mid-Cretaceous, tyrannosaurs diversified and evolved into larger forms, dominating as the primary predators of the late Cretaceous in North America and Asia.”

“By the Late Campanian era, multiple groups of tyrannosaurids, such as Albertosauridae, Daspletosaurini, and Teratophonii, achieved impressive weights of 2 to 3 tons.”

“Their evolutionary journey culminated with the emergence of titanic forms, like tyrannosaurus, the largest known predatory dinosaur ever to exist.”

In this study, paleontologists analyzed an exceptionally large tibia (shin bone) from a Tyrannosaurus specimen sourced from the Hunter Wash Formation in New Mexico’s Kirtland Formation.

The tibia measures 96 cm in length and 12.8 cm in diameter, representing about 84% and 78% of the dimensions of the largest confirmed tyrannosaurus specimens.

Based on comparisons with known tyrannosaurus species, researchers estimated that this prehistoric predator weighed around 4 to 5 tons.

“This discovery marks the oldest giant tyrannosaurus found in North America, potentially identifying it as the earliest known species of Tyrannosaurini,” they noted in their publication.

The tibia exhibits features akin to later tyrannosaurids, specifically tyrannosaurus rex.

Researchers considered three scenarios: the fossil belongs to an unusually large known tyrannosaurus from New Mexico, Bistahieversor sealeyi; it might represent a new lineage of colossal tyrannosaurs; or it could be an early member of the tyrannosaurus rex lineage and its Asian relatives.

After thorough comparisons with other tyrannosaurids and conducting a phylogenetic analysis, the authors determined that the third hypothesis is the most plausible.

“Regardless of which hypothesis is accepted, the unusual size of the Hunter Wash tyrannosaurus is significant as it signifies the presence of a previously unknown large tyrannosaurid in the late Campanian, suggesting their earlier than anticipated evolutionary emergence,” the researchers added.

Paleontologists have long debated the geographic origins of giant tyrannosaurs.

Some theorize that this lineage started in Asia before migrating to North America, while others argue that the massive tyrannosaurus rex originated in the southern part of western North America known as Laramidia.

The newly discovered fossils bolster the theory of a southern Laramidian origin.

“The Hunter Wash tyrannosaurs underscore the remarkable diversity of Laramidian dinosaurs, with smaller albertosaurines and daspletosaurids inhabiting the northern regions, while gigantic tyrannosaurids thrived in the south,” the paleontologists concluded.

The team’s findings were published in a research paper in March 2026 in the journal Scientific Reports.

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NR Longrich et al. 2026. A large tyrannosaurid from the late Cretaceous (Campanian) of North America. Scientific Reports 16, 8371; doi: 10.1038/s41598-026-38600-w