For more than a century, a set of bones resting quietly in New Mexico carried a name that never truly belonged to them. They were filed away, classified, and trusted to represent a familiar dinosaur. But when an international team of researchers, including D. Edward Malinzak of Penn State Lehigh Valley, took a closer look, the fossil seemed to whisper a different story.
Its skull fragments, its vertebrae, even the lines etched into its jaw told a tale that had gone unheard since 1916. The bones, once thought to belong to the well-known hadrosaurid genus Kritosaurus, revealed that they were something entirely new: a massive duck-billed dinosaur that had stayed hidden in plain sight for nearly 90 years.
They named it Ahshiselsaurus wimani, a tribute to the land that preserved it for so long.
A Puzzle Assembled Bone by Bone
The discovery began with a careful anatomical and morphological comparison of the fossil against other known members of the duck-billed hadrosaurid family. This group, as paleontologist Sebastian Dalman explained, once dominated Late Cretaceous ecosystems. “Hadrosauridae, a family of large herbivorous dinosaurs, were among the most abundant dinosaurs of Late Cretaceous terrestrial ecosystems of the Western Interior Basin of North America for about 20 million years,” he said.
The holotype—the original specimen used to define the species—was fragmentary but powerful in what it revealed. Dalman described it as consisting of “an incomplete diagnostic skull, several isolated cranial elements including the right jugal, quadrate, dentary and surangular, and a series of articulated cervical vertebrae.”
These were the pieces the researchers used to rebuild the dinosaur’s identity. By comparing each bone with those of related hadrosaurs, the team began to see subtle but unmistakable differences. Those differences grew into a pattern, and the pattern revealed a dinosaur that demanded its own name.
Malinzak recalled the moment their analysis tipped the scales. “Kritosaurus is still a valid genus with species of its own,” he said. “We took a specimen that was lumped in as an individual of Kritosaurus and determined it had significantly distinct anatomical features to warrant being its own genus and species.”
Clues Hidden in a Skull
Skulls, as the team knew well, are the storytellers of paleontology. They anchor a species’ identity. They contain the shapes and edges that betray ancestry, diet, behavior, and evolution.
“As a general rule … skulls are really the basis for identifying differences in animals,” said Anthony Fiorillo, executive director of the New Mexico Museum of Natural History and Science. “When you have a skull and you’re noticing differences, that carries more weight than, say, you found a toe bone that looks different from that toe bone.”
Those differences reached far beyond taxonomy. They offered a glimpse into ancient migration routes and evolutionary shifts across North America and beyond.
A Dinosaur That Traveled Through Time and Space
After tracing the anatomical differences, the team used the fossil’s physical traits to perform a phylogenetic analysis. This allowed them to map evolutionary relationships and reconstruct long-vanished lineages. What emerged was a picture of ancient movement—dinosaurs spreading north into Canada and south into Central and South America.
Malinzak saw the new species as a point on a much larger map of ancient dispersal. “What we’re noticing is the Southwest is a ‘stock’ for some animals that migrate to the North,” he said. Environmental change, he explained, likely pushed groups northward during certain periods, allowing some lineages to thrive in new territories while others moved south.
During these shifts, the ancestors of Ahshiselsaurus wimani likely expanded their range, replacing older hadrosaur groups as they moved. Later, descendants of even earlier migrants returned to the Southwest, creating a brief period in which multiple lineages coexisted.
This complex back-and-forth across the continent revealed something crucial: the region’s ecosystems were far more diverse than once thought.
“The ecosystem was more diverse than initially considered,” Malinzak said. “It supports the idea that the environment you’re in drives your adaptation. If a new group is well-adapted to an environment it migrates to, it can ‘unseat’ existing species—if the territory has undergone environmental change and the ‘home team’ has yet to adapt.”
He also noted that Ahshiselsaurus wimani appears stratigraphically lower than Kritosaurus, suggesting it is older and shedding new light on the timeline of hadrosaur evolution in the Southwest.
A Discovery That Reaches Into the Classroom
For Malinzak, the research did not end with publication. It became a teaching tool. He brought the methods and calculations from the study into his BIOL 220W course, giving students a chance to see real scientific reasoning unfold from data to conclusion.
“I was able to show my students what information our team used, how we ran the calculations, and how we were able to determine dispersal and divergence events,” he said. “The method helped the students take the idea of studying relationships from a theoretical idea to a tangible process to follow.”
The work has been met with admiration from colleagues. “Dr. Malinzak brings exceptional passion and commitment to his field,” said Aníbal Torres, chief academic officer at Penn State Lehigh Valley. “That dedication consistently drives meaningful and high-quality scholarship.”
What Comes After Naming a Dinosaur
Identifying Ahshiselsaurus wimani is only the beginning. The team plans to revisit other fossils from the region—specimens collected long before modern tools and methods existed.
“This discovery reveals that we should revisit some of the specimens of other animals previously collected in this area,” Malinzak said. He emphasized that the work ahead is both a continuation and a new beginning. “New discoveries and information help us answer current questions, but they also help us to pose new questions as well. Our present work is not the end result.—It’s more like, ‘You made one lap, but there are more laps still to go in the race.’ We’re making progress.”
Why This Discovery Matters
The naming of Ahshiselsaurus wimani is more than the addition of a new species to the dinosaur family tree. It reshapes our understanding of ecosystems that flourished 75 million years ago and reveals how dynamic and interconnected dinosaur populations were across the continent.
It shows that fossils once assumed to be well understood can still surprise us, that ancient ecosystems were richer than we imagined, and that the history of life in the Southwest is still being written bone by bone.
Most importantly, it reminds us that science is a journey, not a destination. Every fossil holds the potential to rewrite a chapter of Earth’s story, and every reexamination opens new paths of curiosity—proof that even after a century of study, the past still has secrets waiting to be found.
