Paleontologists in the United States have uncovered the fossilized remains of a new species of sauropodomorph dinosaur that lived in the northern hemisphere (supercontinent Laurasia) during the Carnian age of the Late Triassic epoch, around 230 million years ago.
Reconstruction of Ahvaytum bahndooiveche, the oldest known low-latitude dinosaur species globally. Image credit: Gabriel Ugueto.
Until now, the origin of dinosaurs was thought to be deeply rooted in the high-latitude southern hemisphere (supercontinent Gondwana).
Gondwanan dinosaur faunas and the oldest known dinosaur occurrence in the northern hemisphere (supercontinent Laurasia) were separated by 6 to 10 million years.
However, the newly-described Laurasian species lived at the same time as the oldest known southern dinosaurs.
Named Ahvaytum bahndooiveche, this sauropodomorph is the oldest known Laurasian dinosaur.
“Ahvaytum bahndooiveche lived in Laurasia during or soon after a period of immense climatic change known as the Carnian pluvial episode that has previously been connected to an early period of diversification of dinosaur species,” said Dr. Dave Lovelace from the University of Wisconsin Geology Museum and his colleagues.
“The climate during that period was much wetter than it had been previously, transforming large, hot stretches of desert into more hospitable habitats for early dinosaurs.”
Ahvaytum bahndooiveche was around 1 m (3 feet) long from head to tail.
“Ahvaytum bahndooiveche was basically the size of a chicken but with a really long tail,” Dr. Lovelace said.
“We think of dinosaurs as giant behemoths, but they didn’t start out that way.”
The fossil remains of Ahvaytum bahndooiveche were discovered in 2013 at Garrett’s Surprise (after undergraduate field assistant Garrett Johnson who discovered the locality), a small exposure of the Popo Agie Formation in Wyoming.
“We have, with these fossils, the oldest equatorial dinosaur in the world — it’s also North America’s oldest dinosaur,” Dr. Lovelace said.
At the same Garrett’s Surprise locality, the paleontologists also found a fossilized bone of a dinosaur-like creature called silesaurid.
“The presence of a 230-million-year-old, low-latitude, early sauropodomorph from the northern hemisphere, along with a silesaurid, challenges the hypothesis of a delayed dinosaurian dispersal out of high-latitude Gondwana,” they said.
“These data fill a critical gap in the early record of sauropodomorph dinosaur evolution and demonstrate widespread geographic distribution by the Mid-Late Carnian age.”
Their results appear in the Zoological Journal of the Linnean Society.
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David M. Lovelace et al. 2025. Rethinking dinosaur origins: oldest known equatorial dinosaur-bearing assemblage (Mid-Late Carnian Popo Agie FM, Wyoming, USA). Zoological Journal of the Linnean Society 203 (1): zlae153; doi: 10.1093/zoolinnean/zlae153
