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Parallel lines seen in sandstone are the traces made by the claw of a giant crocodile that scraped along the muddy bottom of a prehistoric waterway in what is now northeastern British Columbia.Charles Helm/Handout

Long before grizzly bears and mountain lions roamed the wilds of northeastern British Columbia, carnivores that were best avoided in the region included the colossal relatives of modern crocodiles.

Researchers inferred that much after discovering claw marks made about 97 million years ago by the fearsome reptiles, who raked the muddy bottom of a shallow waterway with their claws. The indentations later filled with silt, which became sandstone over the eons, leaving distinctive patterns that were discovered in exposed rock near a highway that runs along the Sukunka River valley north of Tumbler Ridge, B.C.

“The mud consistency was just right” for preserving crocodilian traces, said Guy Plint, a geologist at the University of Western Ontario. “Even the impressions of the scales on their feet can be recognized.”

The marks are similar to those left by crocodiles today, except they are larger. Measurements by Dr. Plint and colleagues suggest the prehistoric crocs measured 9 to 12 metres long and weighed an estimated five tonnes. The team’s results were published last month in the journal Historical Biology.

The crocodile marks were found near dinosaur tracks, which suggests the area alternated between periods as an aquatic and a shoreline environment. At the time, the region was a low lying delta plain, where giant crocodiles may have been the region’s top predators, lurking in lakes and rivers where they could snatch unwary dinosaurs and drag them to their death below the water, Dr. Plint said.

He added that while dinosaurs tend to get more public attention, crocodilian reptiles of the period are fascinating in part because they made it through the major extinction event 66 million years ago that wiped out dinosaurs and a majority of other animal species that were living on Earth at the time.

“Crocs clearly are the great survivors,” Dr. Plint said.

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