Arizona fossils help researchers understand the mysterious period before mass extinction

Smithsonian researchers have linked discoveries within Arizona’s Petrified Forest National Park with a previously unknown transitional period between old and new continental vertebrates.

For the first time, scientists are able to prove that communities of land vertebrates from the older archaic reptiles to the more familiar like turtles were actually living together before a great extinction event at the end of the Triassic period.

“The big importance of this fossil site is that it fills a global gap in our understanding of what continental ecosystems looked [like] at this time frame," said Ben T. Kligman, the lead author of the study.

He says the Triassic period ended with the breakup of supercontinent Pangaea, which made it difficult to pinpoint evidence of when modern land vertebrates first began.

Gavin McCullough, with the Arizona Museum of Natural History, says at the time, Arizona was not in the same geographical place on Earth. Before Pangaea broke up, Arizona was more down by the equator.

"The last 12 or so million years of the Triassic, before the extinction — that led to the Jurassic period afterwards — is kind of shrouded in mystery and there's not a lot of places where they're able to find reliably datable fossils from that time period," McCullough said.

He is unaffiliated with the discovery but says it's an exciting find.

Kligman says the fossil highlights one of the world’s oldest turtle fossils and the jaw bone of a new species of Pterosaur, a small flying reptile. That Pterosaur was also determined to be the oldest in North America.

"So these are these groups that would go on and dominate continental ecosystems after the Triassic period," Kligman said.

This overall project has been nearly two decades in the making since unearthing ancient fossils and rock in Arizona.