Ahvaytum bahndooiveche's fossils were unearthed in Wyoming, part of the ancient supercontinent Laurasia. Radiometric dating indicates the dinosaur lived approximately 230 million years ago, placing it alongside the earliest known dinosaurs from Gondwana, the southern part of Pangea. This finding, published in the Zoological Journal of the Linnean Society, positions Ahvaytum as the oldest known equatorial dinosaur and North America's oldest dinosaur.
"We have, with these fossils, the oldest equatorial dinosaur in the world - it's also North America's oldest dinosaur," said Dave Lovelace, a research scientist at the University of Wisconsin Geology Museum. Lovelace co-led the study with graduate student Aaron Kufner.
Discovered in the Popo Agie Formation, the fossils required years of meticulous study to identify as a new species. While incomplete, the remains-primarily leg bones-enabled researchers to classify Ahvaytum bahndooiveche as a dinosaur and an early relative of sauropods. Unlike its enormous descendants, this dinosaur was roughly the size of a chicken, with a long tail, standing about one foot tall and measuring three feet in length.
"It was basically the size of a chicken but with a really long tail," Lovelace explained. "We think of dinosaurs as these giant behemoths, but they didn't start out that way."
The absence of skull material leaves its diet speculative, but researchers believe it might have been omnivorous, similar to related species. Ahvaytum's fossils were discovered near those of a newly described amphibian, providing insights into its environment. This region's ecosystem developed during the Carnian pluvial episode, a period of significant climatic change around 234 to 232 million years ago. Increased rainfall transformed deserts into lush habitats, fostering early dinosaur diversification.
Radiometric dating confirmed Ahvaytum's age, and older dinosaur-like tracks found in the region suggest that its ancestors or close relatives were already present in Laurasia. "We're kind of filling in some of this story, and we're showing that the ideas that we've held for so long - ideas that were supported by the fragmented evidence that we had - weren't quite right," Lovelace said. "We now have this piece of evidence that shows dinosaurs were here in the northern hemisphere much earlier than we thought."
Ahvaytum bahndooiveche's name honors the Eastern Shoshone Tribe, whose ancestral lands include the fossil discovery site. Tribal elders and middle school students collaborated on the naming process, which translates to "long ago dinosaur" in the Shoshone language. This collaboration reflects a growing partnership between researchers and Indigenous communities to incorporate local knowledge and perspectives into scientific work.
"The continuous relationship developed between Dr. Lovelace, his team, our school district, and our community is one of the most important outcomes of the discovery and naming of Ahvaytum bahndooiveche," said Amanda LeClair-Diaz, a co-author on the paper and member of the Eastern Shoshone and Northern Arapaho Tribes. LeClair-Diaz, the Indian education coordinator at Fort Washakie School, emphasized the importance of reciprocity in research efforts.
The research highlights not only a significant revision in the timeline of dinosaur evolution but also a shift toward more inclusive and collaborative scientific practices.
Research Report:Rethinking dinosaur origins: oldest known equatorial dinosaur-bearing assemblage (mid-late Carnian Popo Agie FM, Wyoming, USA)
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University of Wisconsin-Madison
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