Scientists say they've discovered evidence of a frenzied mating ritual by dinosaurs: long grooves in the ground etched by the pawing of clawed feet.

Such behaviour is seen nowadays in some birds, and the discovery suggests that two-legged, meat-eating dinosaurs called theropods did it about 100 million years ago, the researchers said.

Martin Lockley of the University of Colorado Denver said the dinosaurs, probably males, apparently gathered in groups and "went crazy scraping" with their clawed, three-toed feet to attract mates.

Dinosaur mating ritual

Scrape marks in the rock show the dinosaurs, probably males, apparently gathered in groups and 'went crazy scraping' with their clawed, three-toed feet to attract mates, as in this artist's reconstruction. (Lida Xing and Yujiang Han/University of Colorado Denver)

The beasts were built roughly like smaller versions of a T. rex. Footprints near the grooves suggest a variety of body lengths, up to about 4 metres (16 feet) from snout to tip of the tail.

The grooves they carved are up to 1.8 metres (6 feet) long.

The ritual would have been entertaining to watch, Lockley said in an interview. "These animals would have been really frenzied."

Lockley, an emeritus professor of geology, is an author of a paper on the discovery released Thursday by the journal Scientific Reports. The study was co-authored by Richard McCrea of the Peace Region Paleontological Centre in B.C.

The grooves were found at four sites in Colorado.

For mating or not?

Dinosaur expert Thomas Holtz Jr. of the University of Maryland, who didn't participate in the work, said it's reasonable to think that theropods created the grooves. But was it for mating?

Holtz said he wasn't convinced that the new paper had sufficiently ruled out other explanations. But he added that there's no particular evidence for rejecting the mating idea.

"Whatever behaviour is being recorded here, it is an expression of the fact that dinosaurs—like all animals—did more than hunt and attack and devour and fight and all that limited set of behaviours that popular culture often portrays," Holtz wrote in an email.