Although paleontologists have discussed the origin and spread of dinosaurs for decades, the widely accepted theory is that they appeared in the southern part of the ancient continent of Pangea more than 200 million years ago, and spread only to north millions of years ago. A new study has changed the conversation.

Paleontologists at the University of Wisconsin–Madison (UW–Madison) have announced the discovery of a new dinosaur that challenges conventional theories about the origin and spread of dinosaurs. The location and age of the newly described fossils suggest that dinosaurs roamed the northern regions of Pangea millions of years earlier than previously thought. The findings are detailed in a January 8 study published in Zoological Journal of the Linnean Society.

“We’ve filled in some of this story, and we’ve shown that the ideas that we’ve held for a long time – ideas that are supported by the pieces of evidence that we have – are incorrect,” Dave Si Lovelace of the University of Wisconsin Geology Museum, who led the study, said a UW–Madison statement. “We now have a piece of evidence that shows that dinosaurs were here in the northern hemisphere much earlier than we thought.”

Paleontologists discovered fossils that disprove the theory in what is now Wyoming in 2013. Due to Earth’s shifting tectonic plates, this region was located near the equator more than 200 million years ago in Laurasia, the northern half of Pangea (the southern half is called Gondwana. ). As the remains were dissected, paleontologists were able to attribute the fossils to a new species of dinosaur that they named. Ahvaytum bahndooivechewhich is probably an early one sauropod relative. Ahvaytumhowever, the iconic long-necked herbivores look very different.

“It’s basically the size of a chicken but with a long tail,” Lovelace said. “We think of dinosaurs as these giant behemoths, but they didn’t start out that way.” A mature specimen is just over a foot long (30.5 centimeters) and about three feet tall (91.4 cm).

Perhaps most surprising, however, is the fossil’s age. Lovelace and his colleagues used radioisotopic dating (a method of determining the age of materials by measuring radioactive decay) to determine that the rock layers in which they found the Ahvaytum fossils—and thus almost the remains themselves—are about 230 million years old. It does Ahvaytum the oldest known Laurasian dinosaurs, and are age-matched to the oldest known Gondwanan dinosaurs, according to the study. Dinosaurs first appeared during the Triassic period, about 230 million years ago. This period, which lasted from about 252 to 201 million years ago, saw the rise of the earliest dinos, before they became dominant in the Jurassic period.

“We have, with these fossils, the oldest equatorial dinosaur in the world — it’s also the oldest dinosaur in North America,” Lovelace added. The fact that the oldest known Laurasian dinosaur is close to the age of the earliest known Gondwanan dinosaurs challenges the theory that dinosaurs originated in the south of the old continent and only spread north million- million years ago.

The site of the discovery is within the ancestral lands of the Eastern Shoshone Tribe. As a result, the researchers collaborated with tribal members in their work, and included Eastern Shoshone elders and middle school students in choosing a new name for the dinosaur. Ahvaytum bahndooiveche roughly translates to “long ago dinosaur” in the Eastern Shoshone language.

The region has also yielded additional finds. The team identified an early dinosaur-like footprint in the older rock layers, meaning that dinosaurs or dinosaur-related creatures called Laurasia home even before that. Ahvaytum. Paleontologists also discovered the fossil of a newly described amphibianwhich is also named in the Eastern Shoshone language.

Challenging long-standing theories about how dinosaurs spread across Pangea, the discovery of chicken size. Ahvaytum finally painting a clearer picture of the creatures that walked the Earth—and where—millions of years before us.