Paleontologists have revealed a mᴀssive tyrannosaur shinbone from New Mexico’s Kirtland Formation that proves giant tyrannosaurids dominated southern North America as early as 74 million years ago—millions of years before Tyrannosaurus rex rose to fame.

Described in a March 2026 Scientific Reports paper by Nicholas Longrich and colleagues, the 96-cm-long tibia (specimen NMMNHP 25085) was collected decades ago from the Hunter Wash Member of the Bisti/De-na-zin Wilderness. High-precision dating of the marine-influenced strata places it at approximately 74 million years ago (late Campanian).

The bone is robust and pneumatic, with proportions matching later tyrannosaurines. Estimated body mᴀss reaches 4.7–5 tons—roughly 75–80% the size of the largest T. rex (e.g., Sue)—making it the oldest known giant tyrannosaur from North America and a prime candidate for an early member of Tyrannosaurini, the clade that includes T. rex, Tarbosaurus, and Zhuchengtyrannus.

Lead author Longrich notes: “This specimen shows that the lineage leading to T. rex had already achieved enormous size and robust build in the southern Western Interior by the late Campanian.” The find challenges the long-held view that giant tyrannosaurs evolved only in the Maastrichtian of northern Laramidia; instead, they appear to have originated farther south.

Recovered alongside hadrosaurs and ceratopsians in coastal floodplain deposits, the predator likely ambushed duckbills and horned dinosaurs in a lush, river-dominated landscape bordering the receding Western Interior Seaway. Its discovery reinforces New Mexico’s status as a key window into tyrannosaur evolution.

As more fragments from the same horizon are re-examined, this “Hunter Wash giant” promises to illuminate how T. rex’s ancestors first seized dominance across the continent—proving that the tyrant lizard’s reign began not in the north, but in the sun-baked badlands of ancient New Mexico.