Paleontologists have formally identified a massive, previously unknown species of plant-eating dinosaur from northwestern New Mexico, marking a significant revision to the evolutionary history of North America's Late Cretaceous period. The new giant, designated *Ahshislesaurus wimani*, was announced in a scientific bulletin from the New Mexico Museum of Natural History and Science in October 2025. This discovery centers on fossils that were initially recovered in 1916 by fossil hunter John B. Reeside Jr. from the Ah-Shi-Sle-Pah Wilderness in San Juan County.
For decades, these remains were classified under the established hadrosaur genus *Kritosaurus navajovius*. However, contemporary, rigorous analysis conducted by an international consortium confirmed that the specimens represent an entirely distinct lineage, necessitating the new species classification. The name *Ahshislesaurus* is derived from the Navajo phrase for the wilderness area, meaning "salt, it is gray," combined with the Greek term for lizard. The specific epithet, *wimani*, honors Swedish paleontologist Carl Wiman, who examined the materials in the 1930s. Researchers, including Sebastian Dalman, noted that this finding builds upon nearly a century of prior work.
Estimates based on the recovered partial cranium, jaw segments, and neck vertebrae suggest *Ahshislesaurus wimani* was a substantial herbivore, potentially exceeding 10 meters in length and weighing close to 9 tons. This duck-billed dinosaur inhabited the marshy floodplains of ancient southern Laramidia approximately 75 million years ago. A key feature distinguishing *Ahshislesaurus wimani* from other hadrosaurs is its remarkably flat and sturdy skull structure, contrasting with the more ornamented skulls found in related species. Its broad, duck-like beak was adapted for efficiently consuming soft foliage.
The finding strongly implies that existing models detailing the diversification of hadrosaurs in the Late Cretaceous require comprehensive review. The Ah-Shi-Sle-Pah region, characterized by its dramatically eroded badlands, was a rich ecosystem supporting not only *Ahshislesaurus* but also horned ceratopsians like *Navajoceratops* and apex predators colloquially known as the 'Bisti Beast.'
The comprehensive research, which synthesized decades-old archival specimens, was guided by paleontologist Sebastian Dalman and involved a collaborative team spanning five institutions across the United States and Europe. This work opens a new avenue for inquiry, suggesting that other unassigned skeletal elements from the same locale—including various femurs and humeri—may belong to juvenile and adult *Ahshislesaurus* individuals. Furthermore, the discovery contributes to growing evidence that the diversity of these herbivores in southern Laramidia during the Campanian age may have been significantly underestimated.