A team made up of researchers from New Mexico Museum of Natural History and Science and biologist D. Edward Malinzak, a professor at Penn State Lehigh Valley, determined that A fossil discovered in 1916 in New Mexico does not belong to the genus Kritosaurusas it had been maintained since 1935. The new analysis, the results of which were published in the Bulletin of the New Mexico Museum of Natural History and Science, demonstrates that the specimen represents a different species, named Ahshiselsaurus Wimani.
THE reclassification is based on a set of fossils that includes an incomplete diagnostic skullseveral isolated cranial elements, including the right jugal, quadrate, dentary and surangular, as well as an articulated series of cervical vertebrae. This material constitutes the holotype which formally defines the species. A detailed examination revealed that proportions and anatomical features of these bones do not correspond to those of Kritosaurusgenus which remains valid but whose type material clearly differs from the fossil studied.
What the investigation revealed
To assess these differences, the team compared the specimen’s anatomy with that of other North American hadrosaurids. Hadrosaurids, known as dinosaurs “duck-billed”were one of the most abundant lineages of herbivores in terrestrial ecosystems from the western interior of North America for about 20 million years. According to paleontologist Sebastian Dalman, lead author of the study, the cranial features were decisive, given that the skull is one of the most reliable elements for distinguishing species in this group.
Anthony Fiorilloexecutive director of the museum and co-author of the work, underlines this idea emphasizing that, when differences are observed at the skull level, these carry much more weight than variations in fewer diagnostic itemslike a foot bone. In addition to the osteological analysis, the researchers carried out a phylogenetic study based on anatomical characteristics that place Ahshiselsaurus Wimani in a different position relative to Kritosaurussupporting reclassification.
Migration conditions
The conclusions also provide information on migration and diversification patterns hadrosaurids in the southwestern United States during the Late Cretaceous. Malinzak explains that the new discovery matches previous evidence which suggests faunal exchanges between North and South America, as well as northward movements towards Canada. The data indicates that different lineages could temporarily coexist in the region and that some replaced others at different times.
The team also highlights that Ahshiselsaurus Wimani appears stratigraphically below Kritosauruswhich suggests that it’s older. For Malinzak, this relative antiquity and the diversity observed at the levels studied support the idea that the The American southwest offered an environment especially favorable for the proliferation of different groups of dinosaurs. “The ecosystem was more diverse than initially thought,” he says, pointing out that environmental changes could have favored the expansion of certain lineages to the detriment of others.
educational dimension
The study also had a educational dimension. Malinzak incorporated the methodology used, such as comparative analyzes and the study of evolutionary relationships, into his biology classes, to show students how the dispersal and divergence processes are reconstructed from specific fossil data.
The identification of Ahshiselsaurus Wimani opens new avenues of research. The team plans to examine other historical fossils from the southwestern United States that may have been inaccurately assigned. According to Malinzak, The discovery does not represent an end point, but rather progress in a continuous process: “Our current work is not the final result; it is rather about completing one lap in a race: there is still much to do.” Understanding the evolution and ecological pressures that shaped these lineages will allow us to continue to refine the Cretaceous history of the region.
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