By Stephen Beech

Dinosaurs roamed the northern hemisphere millions of years earlier than previously thought, according to new research.

Fossils identified as a new species after being discovered in Wyoming are estimated to be around 230 million years old - making it North America's oldest dinosaur.

How and when dinosaurs first emerged and spread across Earth more than 200 million years ago has been a source of debate among paleontologists for several years.

The mainstream view has held that dinosaurs emerged on Gondwana - the southern portion of the ancient supercontinent Pangea - millions of years before spreading to the northern half, named Laurasia.

But now, the newly described dinosaur is challenging that narrative, with evidence that the reptiles were present in the northern hemisphere millions of years earlier than previously known.

A team from the University of Wisconsin-Madison has been analyzing the fossil remains since they were first discovered in 2013 in present-day Wyoming, an area that was near the equator on Laurasia.

The creature, named Ahvaytum bahndooiveche, is now the oldest known Laurasian dinosaur.

And with fossils estimated to be around 230 million years old, it's comparable in age to the earliest known Gondwanan dinosaurs, according to the findings published in the Zoological Journal of the Linnean Society.

Dr. Dave Lovelace, a research scientist at the University of Wisconsin Geology Museum who co-led the work with graduate student Aaron Kufner, said: "We have, with these fossils, the oldest equatorial dinosaur in the world - it's also North America's oldest dinosaur."

Discovered in a layer of rock known as the Popo Agie Formation, it took years of intricate work by Dr. Lovelace and his colleagues to analyze the fossils, establish them as a new dinosaur species and determine their estimated age.

While the team doesn't have a complete specimen, they found enough fossils, particularly parts of the species' legs, to positively identify Ahvaytum bahndooiveche as a dinosaur, and likely as a very early sauropod relative.

Sauropods were a group of herbivorous dinosaurs that included some gigantic species like those in the aptly named group of titanosaurs.

The distantly related Ahvaytum bahndooiveche lived millions of years earlier and was much smaller.

Dr. Lovelace said: "It was basically the size of a chicken but with a really long tail

"We think of dinosaurs as these giant behemoths, but they didn't start out that way."

He says the type specimen of Ahvaytum bahndooiveche, which was full-grown but could have been slightly bigger at its maximum age, stood a little over one foot tall and was around three feet long from head to tail.

Although researchers haven't found its skull material, which could help illuminate what it ate, other closely related early sauropod-line dinosaurs were eating meat and would likely have been omnivorous.

The researchers found the few known bones of Ahvaytum in a layer of rock just a little bit above those of a newly described amphibian that they also discovered.

The evidence suggests that 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.

Dr. Lovelace says the climate during that period, lasting from about 234 to 232 million years ago, was much wetter than it had been previously, transforming large, hot stretches of desert into more hospitable habitats for early dinosaurs.

The research team performed high-precision radioisotopic dating of rocks in the formation that held Ahvaytum's fossils, which revealed that the dinosaur was present in the northern hemisphere around 230 million years ago.

The team also found an early dinosaur-like track in slightly older rocks, demonstrating that dinosaurs or their cousins were already in the region a few million years prior to Ahvaytum.

Dr. Lovelace said: "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.

"We now have this piece of evidence that shows dinosaurs were here in the northern hemisphere much earlier than we thought."

While the team is confident they've discovered North America's oldest dinosaur, it's also the first dinosaur species to be named in the language of the Eastern Shoshone Tribe, whose ancestral lands include the site where the fossils were found.

Eastern Shoshone tribal elders and middle school students were integral to the naming process.

Ahvaytum bahndooiveche broadly translates to "long ago dinosaur" in the Shoshone language.

Several tribal members also teamed up with Dr. Lovelace and his colleagues as the researchers sought to evolve their field practices and better respect the land by incorporating the knowledge and perspectives of the Indigenous peoples into their work.

Dr. Amanda LeClair-Diaz, a co-author on the paper and a member of the Eastern Shoshone and Northern Arapaho Tribes, said: "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."

She added: "Typically, the research process in communities, especially Indigenous communities, has been one-sided, with the researchers fully benefiting from studies.

"The work we have done with Dr. Lovelace breaks this cycle and creates an opportunity for reciprocity in the research process."

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