Paleontologists believe that all non-avian dinosaurs were wiped out when a giant asteroid or comet collided with Earth some 65 million years ago, resulting in huge clouds of dust that blocked the Sun’s rays from reaching Earth’s surface. But the origins of dinosaurs have been less understood. In a new study, published in the journal Nature Communications, researchers argue that dinosaurs diversified explosively in the mid-Carnian, at a time of major climate and floral change and the extinction of key plant-eaters, which the dinosaurs opportunistically replaced.

In the new study, evidence is provided to match the two events: the mid-Carnian extinction (known as the Carnian Pluvial Episode, or CPE) and the initial diversification of dinosaurs.

Dinosaurs had originated much earlier, at the beginning of the Triassic period, some 245 million years ago, but they remained very rare until the shock events of CPE 13 million years later.

The study shows just when dinosaurs took over by using detailed evidence from rock sequences in the Dolomites, in north Italy — here the dinosaurs are detected from their footprints.

First there were no dinosaur tracks, and then there were many. This marks the moment of their explosion, and the rock successions in the Dolomites are well dated.

Comparison with rock successions in Argentina and Brazil, here the first extensive skeletons of dinosaurs occur, show the explosion happened at the same time there as well.

“We were excited to see that the footprints and skeletons told the same story,” said study lead author Dr. Massimo Bernardi, from the MUSE-Museo delle Scienze in Trento, Italy, and the University of Bristol, UK.

“We had been studying the footprints in the Dolomites for some time, and it’s amazing how clear cut the change from ‘no dinosaurs’ to ‘all dinosaurs’ was.”

The point of explosion of dinosaurs matches the end of the CPE event, a time when climates shuttled from dry to humid and back to dry again.

It was long suspected that CPE had caused upheavals among life on land and in the sea, but the details were not clear.

Then, in 2015, dating of rock sections and measurement of oxygen and carbon values showed just what had happened.

There were massive eruptions in western Canada, represented today by the great Wrangellia basalts — these drove bursts of global warming, acid rain, and killing on land and in the oceans.

“We had detected evidence for the climate change in the Dolomites. There were four pulses of warming and climate perturbation, all within a million years or so. This must have led to repeated extinctions,” said co-author Dr. Piero Gianolla, from the University of Ferrara, Italy.

“The discovery of the existence of a link between the first diversification of dinosaurs and a global mass extinction is important,” said co-author Professor Mike Benton, from the University of Bristol.

“The extinction didn’t just clear the way for the age of the dinosaurs, but also for the origins of many modern groups, including lizards, crocodiles, turtles, and mammals — key land animals today.”

_____

Massimo Bernardi et al. 2018. Dinosaur diversification linked with the Carnian Pluvial Episode. Nature Communications 9, article number: 1499; doi: 10.1038/s41467-018-03996-1