Nine-ton giant dinosaur with duck-like face discovered in New Mexico

A new duck-billed dinosaur from northern New Mexico turns out to be a species we did not have on the books. It lived about 75 million years ago in the late Cretaceous, when rivers laced a warm, coastal plain.

The fossils were first collected in 1916, but then filed under a different name for decades. Careful re-study shows those bones belong to a completely new animal species.

What the team found

The reanalysis identifies the duck-billed skull as a new species of dinosaur, namely Ahshislesaurus wimani. This is based on features of the jaw and skull roof reported in a recent, peer-reviewed paper.

Lead scientist Spencer G. Lucas of the New Mexico Museum of Natural History and Science (NMMNHS) led the classification effort with collaborators in the United States and Slovakia.

The animal is a member of the Hadrosauridae family. This group includes plant-eating dinosaurs that have broad, beak-like snouts, known informally as duck-bills. This one lacked a tall head crest and had a flat profile.

Based on available fossil data, the animal reached more than 35 feet (10 meters) in length and weighed about 9 tons. “This new hadrosaur just adds to my conviction that there are many, many new dinosaurs still out there waiting to be unearthed!” said Lucas.

The bones came from the Ah-shi-sle-pah Wilderness in San Juan County. The skull and neck bones were stored for years under the older name Kritosaurus navajovius, before being re-examined.

Why this duck-billed dinosaur matters

Hadrosaurs were among the most common big herbivores in North America during the last stretch of the Cretaceous. For roughly 20 million years, they browsed in river deltas and floodplains in huge numbers, according to a foundational chapter by Horner and colleagues.

Ahshislesaurus sits within the Saurolophinae, a subgroup of flat-headed hadrosaurids, defined here as the branch that generally lacks hollow, tube-like crests. This sets it apart from the flamboyant lambeosaurines.

Finding a new saurolophine in New Mexico strengthens the case for regional diversity in western North America. That distribution hints at ancient barriers and local habitats shaping dinosaur evolution.

The animal also expands the roster of dinosaurs from the Kirtland Formation. New Mexico is a hotbed for Late Cretaceous discoveries that fill gaps left by better known sites in Montana and Alberta.

How the puzzle was solved

The study team contrasted the skull with similar hadrosaurs and mapped traits on a family tree. That phylogenetic, family-tree analysis used shared traits, and found Ahshislesaurus most closely related to Naashoibitosaurus from nearby rocks.

In addition, researchers also ran a Bayesian analysis alongside a parsimony analysis to check stability. Both approaches converged on a similar placement for the new species in the hadrosaur family tree.

Distinctive features included a robust cheek region and a quadrate bone with a posterodorsally set head. The lower jaw’s front end is deep, giving the tooth row a strong anchor.

The specimen is the holotype, the single reference skeleton that anchors a species name. It includes an incomplete skull, jaw elements, and several neck vertebrae.

Life in late Cretaceous New Mexico

Ahshislesaurus browsed in a river-rich ecosystem alongside armor-plated ankylosaurs and horned dinosaurs like Navajoceratops. Predators included tyrannosaur relatives stalking the channels and levees.

The age is the Campanian, a slice of late Cretaceous time, roughly 83 to 72 million years ago. The rock unit is the Hunter Wash Member of the Kirtland Formation.

The region was part of Laramidia, the western landmass of North America that was split by a shallow, inland sea. That geography helped isolate dinosaur populations, which can then drive local variation.

Plant life would have included conifers and flowering plants, providing ample browse for a heavy, wide-jawed grazer. The high tooth counts of hadrosaurs suited constant chewing.

What the name tells us

Ahshislesaurus honors the Ah-shi-sle-pah landscape where the duck-billed dinosaur was found. The species name wimani honors Carl Wiman, an early researcher who worked on San Juan Basin fossils.

Naming rules in zoology require a clear diagnosis and a permanent record. The team registered the name and documented it with comparative figures and measurements.

A note on the bigger picture

The find tightens the picture of southern Laramidian hadrosaurs. Ahshislesaurus and Naashoibitosaurus form a flat-headed branch that lived alongside deeper-snouted kritosaurins, all in close quarters.

Interestingly, Lambeosaurines with tube-like crests also lived in the region, including Parasaurolophus. Recent work re-describing that animal’s crest shows how diverse headgear evolved in these dinosaurs.

Hadrosaurs did not just differ by head shape. They also varied in jaw depth, cheekbone geometry, and tooth count, which likely reflects diet and habitat differences.

As more museum collections are re-examined, expect more name changes and new names. Some misassigned fossils will become the keys to species we have not formally recognized yet.

The study is published in New Mexico Museum of Natural History and Science Bulletin 101.

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