For decades, paleontologists have debated how and when dinosaurs emerged and spread across the planet more than 200 million years ago. The prevailing theory suggested that dinosaurs first arose in the southern part of the ancient supercontinent Pangaea, known as Gondwana, before expanding northward into Laurasia. However, recent discoveries are reshaping this narrative.
Paleontologists from the University of Wisconsin–Madison have uncovered fossils in Wyoming that challenge previous assumptions. These remains, belonging to a newly described species named Ahvaytum bahndooiveche, suggest that dinosaurs existed in the northern hemisphere millions of years earlier than previously believed. Estimated to be around 230 million years old, the fossils place this species among the earliest known dinosaurs and make it the oldest dinosaur discovered in North America.
The discovery site, located in what is now Wyoming but once sat near the equator in Laurasia, yielded fragments of Ahvaytum bahndooiveche, including parts of its limbs. While not a complete skeleton—an uncommon find for early dinosaurs—the fossils were enough to confirm that this species was likely an early relative of the massive, herbivorous sauropods. However, unlike its later relatives, Ahvaytum bahndooiveche was modest in size. Fully grown, it stood just over a foot tall and measured about three feet in length, including a long tail.

Think of a chicken with an incredibly long tail, explained Dave Lovelace, a scientist at the University of Wisconsin’s Geology Museum. Dinosaurs didn’t start as the colossal creatures we often imagine; they began small.
The species’ diet remains unclear, as no cranial material was recovered. However, early sauropod relatives are thought to have been omnivorous, consuming both plants and small animals.
The fossils were discovered in the Popo Agie Formation, a geological layer that also contained remains of other prehistoric creatures, including an amphibian described by the same team. These findings date back to the Carnian Pluvial Episode, a period of dramatic climatic changes about 234 to 232 million years ago. During this time, arid deserts transformed into wetter environments, creating more favorable habitats for emerging dinosaur species.

Advanced radiometric dating of the formation’s rocks confirmed the age of Ahvaytum bahndooiveche. Additional evidence, such as slightly older dinosaur tracks in the region, suggests that dinosaurs or their close relatives were present in the northern hemisphere even earlier.
The name Ahvaytum bahndooiveche holds special significance. It translates roughly to “dinosaur of the old times” in the language of the Eastern Shoshone, whose ancestral lands include the discovery site. Tribal elders and students collaborated with the researchers to name the species, fostering a respectful partnership that acknowledged Indigenous ties to the region.
Lovelace emphasized the importance of integrating Indigenous knowledge into paleontological research. By involving the Eastern Shoshone in this process, we’re not just uncovering the history of dinosaurs but also honoring the history of the people connected to this land, he said.
This small dinosaur challenges long-held beliefs about the timing and geography of dinosaur evolution, proving that these creatures were more widespread earlier than assumed. As Lovelace noted, We’re filling in the gaps of a story that has been pieced together over decades, and this discovery shifts the timeline significantly.
SOURCES
University of Wisconsin-Madison
David Lovelace et al., Rethinking dinosaur origins: oldest known equatorial dinosaur-bearing assemblage (mid-late Carnian Popo Agie FM, Wyoming, USA). Zoological Journal of the Linnean Society, Volume 203, Issue 1, January 2025, zlae153. DOI: 10.1093/zoolinnean/zlae153
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