Why America Has So Many Great Dinosaurs: 'We Are in the Goldilocks Window'

North America is currently in the "Goldilocks window" for finding dinosaur fossils from the Late Cretaceous period, a researcher has said.

The Cretaceous period is a geological period that lasted between 145.5 million and 65.5 million years ago, ending with the catastrophic dinosaur extinction event.

The dinosaurs of the last 10 million years of the Cretaceous period in North America are some of the most famous in the world. They include the sharp-toothed Tyrannosaurus, the horned Triceratops, and the duck-billed hadrosaurs.

T-rex walking
A stock illustration depicts a T-rex walking along the ancient Earth. Some of the most famous dinosaurs ever are thought to have lived in North America, including Tyrannosaurus. Getty/Orla

Western North America, in particular, has been one of the greatest sources of dinosaur fossils in the world. According to a study on fossil preservation published Monday, fossils preserved in North America's Western Interior Basin record an "exceptional peak" in the diversification of dinosaur fossils towards the end of the Cretaceous period.

So what is it about North America that makes it so abundant in fossils? Is it that this region was particularly habitable for dinosaurs, making it a global hotspot for diversification?

Not necessarily, according to Eric Roberts, head of earth and environmental science at James Cook University in Australia and author of the aforementioned study.

"The real question is why are there so many dinosaurs and other vertebrate fossils preserved across the part of Western North America in rocks spanning such a short duration?" Roberts told Newsweek.

The answer, he said, is that the time was right for these fossils to be preserved due to widespread volcanic activity, which produced huge amounts of sediment.

"The tectonic setting involving active arc volcanism, as well as intraplate volcanism, produced voluminous and widespread volcanic sedimentary deposits, primarily in the form of ash fall deposits, that we were able to apply the highest precision dating techniques currently available to start to unravel questions like this," Roberts said.

In addition, this sedimentary burial action was taking place along vast environmental differences from north to south along the western basin, hence greater diversity in the fossils.

But there is another crucial factor: luck. Part of the reason so many diverse fossils have been found in North America since we started looking is because of when we started looking.

According to Roberts, the rocks that preserve the fossil records just so happen to have been recently uplifted and eroded by natural processes.

"In lay terms, we are in the Goldilocks window for finding fossils in the Late Cretaceous of Western North America because the rocks have been recently uplifted, geologically speaking, due to uplift of the Colorado Plateau, coupled with a generally arid/semi-arid climate across much of the region—meaning that the exposed rock record is conspicuously poorly vegetated, allowing for enhanced erosion and fossil discovery," he said.

One example of newly-exposed rock revealing dinosaur activity is the discovery of enormous footprints found as a result of the drying of a river in Texas this year. The river, exhausted by drought, shrunk in size revealing previously unseen dinosaur footprints beneath the waterline.