Dinosaurs in the northern hemisphere millions of years earlier than believed

How and when did dinosaurs emerge and spread across Earth more than 200 million years ago? This question has for decades been a source of debate among paleontologists grappling with fragmented fossil records. The dominant view has been that dinosaurs emerged in the southern part of the ancient supercontinent Pangea, called Gondwana, millions of years before spreading to the northern half, called Laurasia.

But now, a newly described dinosaur whose fossil remains were discovered by paleontologists at the University of Wisconsin-Madison (United States) calls that theory into question, with evidence that such animals were present in the northern hemisphere millions of years before what was known until now.

The research team, led by David Lovelace of the aforementioned university, has been analyzing the fossil remains since they were discovered in 2013 at a paleontological site located in what is now Wyoming. When the fossilized animal was alive, that territory was near the equator and was part of Laurasia.

The dinosaur, which has been given the name Ahvaytum bahndooiveche, is estimated to date back about 230 million years. That makes it the oldest known Laurasian dinosaur, as well as the oldest in North America. Furthermore, its age is comparable to that of the first known Gondwanan dinosaurs.

Of the oldest dinosaurs, there are hardly any complete fossil specimens. The same is true for Ahvaytum bahndooiveche, although in this case enough fossil remains have been found, particularly parts of the legs, to clearly identify Ahvaytum bahndooiveche as a dinosaur, and probably as a distant and very primitive evolutionary relative of sauropods. Sauropods were a group of herbivorous dinosaurs that included some species with gigantic body sizes such as titanosaurs.

Artistic recreation of the approximate appearance that a typical adult individual of Ahvaytum bahndooiveche must have had in life. (Illustration: Gabriel Ugueto)

The Ahvaytum bahndooiveche lived millions of years earlier and was much smaller than those beasts. Its body size barely exceeded that of a rooster, although its tail was very long. The remains found of the Ahvaytum bahndooiveche correspond to an adult individual of the species, and measured just over half a meter in height and around a meter in length from head to tail.

The study on this dinosaur is titled “Rethinking dinosaur origins: oldest known equatorial dinosaur-bearing assemblage (mid-late Carnian Popo Agie FM, Wyoming, USA)”. And it has been published in the academic journal Zoological Journal of the Linnean Society. (Fountain: NCYT by Amazings)