A forest fire has left its traces for science to find even though this particular natural blaze happened some 66 million years ago, researchers say.

Fossil evidence locked in stone in southern Saskatchewan in Canada shows prehistoric timberlands recovered from such conflagrations in much same way they do today, researchers from the Royal Saskatchewan Museum and McGill University in Montreal found.

It's the first fossil evidence ever found of the ecology of a forest fire and how the plants regrew after fires raged in the last days before the Earth's dinosaurs went extinct, they said.

"Excavating plant fossils preserved in rocks deposited during the last days of the dinosaurs, we found some preserved with abundant fossilized charcoal and others without it," McGill macroevolutionist Hans Larsson said. "From this, we were able to reconstruct what the Cretaceous forests looked like with and without fire disturbance."

The present day badlands of Saskatchewan are dry and treeless grasslands, but in the Cretaceous period they were lowland, swampy forests, around 20 degrees warmer, with up to six times as much rain as today, the scientists said.

With a forest canopy of towering sequoia trees and smaller plants that grew low on the ground between them, the region could have resembled today's Pacific Coast of North America, they said.

At the site of the prehistoric fire, the plants found were what would be expected as a modern forest recovers from a fire, experts said. Plants like birch and alder were common in early stages of recovery.

At a nearby site that hadn't experienced fires, sequoia and gingko trees would have been thriving in a mature forest, they said.

"The abundant plant fossils also allowed us for the first time to estimate climate conditions for the closing period of the dinosaurs in southwestern Canada, and provides one more clue to reveal what the ecology was like just before they went extinct," Larsson said.

Since forest fires are known to have an impact on the biodiversity of both plants and animals, the ancient ecological findings can yield clues to the existing biodiversity just before the mass extinctions of dinosaurs, the researchers reported in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

In the same layers of rock as the ancient burned forest the scientists unearthed fossils of ancient crocodiles, turtles and dinosaurs, including Tyrannosaurus rex. 

"We won't be able to fully understand the extinction dynamics until we understand what normal ecological processes were going on in the background," Larsson said.