Ahshislesaurus

MEANING: Gray salt lizard

PERIOD: Late Cretaceous

CONTINENT: North America

Ahshislesaurus is a saurolophine hadrosaur that lived during the Late Cretaceous period in what is now New Mexico, in the United States.

Abstract from paper: A new saurolophine hadrosaurid dinosaur, Ahshislesaurus wimani gen et sp. nov., from the lower Hunter Wash Member of the lower Kirtland Formation (~75.02 Ma) of New Mexico is described. The specimen was briefly described before and referred to the stratigraphically younger Kritosaurus navajovius, which is known from the De-na-zin Member (~73.83–73.49 Ma) of the uppermost Kirtland Formation. The holotype of A. wimani consists of an incomplete diagnostic skull, several isolated cranial elements including the right jugal, quadrate, dentary, and surangular, and a series of articulated cervical vertebrae. In addition to the holotype of A. wimani, several specimens from the same strata may also belong to this newly identified species, including a well-preserved left dentary and a partial skeleton, as well as two humeri, one belonging to a large adult and the other to a juvenile. The skull of A. wimani preserves several taxonomically informative characters that show close affinities with the stratigraphically younger Naashoibitosaurus ostromi from the De-na-zin Member. Together with Naashoibitosaurus, Ahshislesaurus forms a potentially novel clade of flat-headed saurolophine hadrosaurids. This clade suggests the saurolophines were a taxonomically diverse group, which, during the last 20 million years of the Cretaceous, were among the dominant herbivorous dinosaurs in southern Laramidia. Recognition of a new hadrosaurid species from New Mexico also provides further evidence for latitudinal variation in the hadrosaurid fauna during the Late Cretaceous in Laramidia.

Ahshislesaurus is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene (K–Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K–Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Ahshislesaurus is a saurolophine hadrosaur. The hadrosauridae, often called "duck-billed dinosaurs," were some of the most successful herbivores of the Late Cretaceous. They belonged to the broader group of ornithopods within the ornithischia, and were especially notable for their complex rows of tightly packed teeth, or dental batteries, that allowed them to efficiently process tough plant material. Hadrosaurs came in a wide range of sizes and shapes, but many shared traits like broad beaks, strong hindlimbs, and often elaborate crests on their heads. They were widespread, thriving across North America, Asia, and Europe, and represent one of the final flourishing groups of non-avian dinosaurs before the end-Cretaceous extinction.

Saurolophinae is a major subgroup distinguished by generally lacking the hollow, tube-like crests seen in their sister group, the Lambeosaurinae. While some saurolophines still had crests, they were typically solid and not as elaborate in structure. Many saurolophines had more robust builds and are thought to have inhabited a variety of environments, from coastal plains to inland floodplains. This showcases the adaptability and ecological dominance that made hadrosaurs a cornerstone of Late Cretaceous ecosystems.