Dinosaurs arrived in the northern hemisphere millions of years before

Jan. 8 () –

A dinosaur newly described by fossils discovered in 2013 points to the presence of these now extinct animals in the northern hemisphere millions of years earlier than previously known.

How and when did dinosaurs emerge and spread across the planet more than 200 million years ago? This question has been a source of debate for decades among paleontologists grappling with fragmented fossil records. Mainstream opinion has held that reptiles emerged in the southern part of the ancient supercontinent Pangea called Gondwana millions of years ago before spreading to the northern half called Laurasia. The new research challenges this narrative.

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 in Laurasia. The creature, called Ahvaytum bahndooiveche, is now the oldest known Laurasian dinosaur and, with fossils estimated to be around 230 million years old, It is comparable in age to the earliest known Gondwanan dinosaurs.

UW-Madison scientists and their research partners detail their discovery on January 8, 2025 in the Zoological Journal of the Linnean Society.

“With these fossils, we have the oldest equatorial dinosaur in the world; it is also the oldest dinosaur in North America,” he says in a statement Dave Lovelace, a research scientist at the University of Wisconsin Museum of Geology who co-led the work with graduate student Aaron Kufner.

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

Although the team does not have a complete specimen (which is extremely rare for early dinosaurs), they did find enough fossils, particularly parts of the species’ legs, to positively identify Ahvaytum bahndooiveche as a dinosaur, and probably as a very early relative of sauropods. Sauropods were a group of herbivorous dinosaurs that included some species famous for their gigantic size, such as the appropriately named titanosaur group. Ahvaytum bahndooiveche, a distant relative, lived millions of years earlier and was smaller, much smaller.

THE SIZE OF A CHICKEN

“It was basically the size of a chicken, but with a very long tail.” says Lovelace. “We think of dinosaurs as these giant colossi, but they didn’t start out that way.”

In fact, the type specimen of Ahvaytum bahndooiveche, which was an adult but may have been a little larger at its full age, was a little over a foot tall and about three feet long from head to tail. Although scientists have not found material from its skull, which could help clarify what it ate, other closely related early dinosaurs from the sauropod line They ate meat and were probably omnivores.

The researchers found Ahvaytum’s few known bones in a layer of rock just above those of a newly described amphibian they also discovered. Evidence suggests that Ahvaytum bahndooiveche lived in Laurasia during or shortly after a period of immense climate change known as the Carnian pluvial episode that had previously been linked to an early period of diversification of dinosaur species.

The weather during that period, which lasted from about 234 to 232 million years agowas much wetter than before, transforming large, hot expanses of desert into more hospitable habitats for the first dinosaurs.

Lovelace and his colleagues performed high-precision radioisotope dating of rocks in the formation containing the Ahvaytum fossils, which revealed that the dinosaur was present in the northern hemisphere about 230 million years ago. The researchers also found a footprint similar to that of an early dinosaur in slightly older rocks, proving that dinosaurs or their cousins ​​were already in the region a few million years before Ahvaytum.

“We’re filling in part of this story and showing that the ideas we’ve held for so long—ideas that were supported by the fragmentary evidence we had—were not entirely correct,” Lovelace says. “Now we have this piece of evidence showing that dinosaurs were here in the northern hemisphere much earlier than we thought.”