Just like modern birds, gigantic dinosaurs engaged in a ritual of dance to woo their mates, suggests new research.
The findings are based on huge scrape marks left behind in 100 million years old rocks in the prehistoric Dakota sandstone of western Colorado, US.
"These are the first sites with evidence of dinosaur mating display rituals ever discovered, and the first physical evidence of courtship behaviour," said lead researcher Martin Lockley, professor of geology at the University of Colorado - Denver.
This is physical evidence of pre-historic "foreplay" that is very similar to birds today, said Lockley, who also discovered evidence of mating areas at Dinosaur Ridge, a National Natural Landmark, just west of Denver.
"Modern birds using scrape ceremony courtship usually do so near their final nesting sites. So the fossil scrape evidence offers a tantalising clue that dinosaurs in 'heat' may have gathered here millions of years ago to breed and then nest nearby," he said.
This new fossil evidence supports theories about the nature of dinosaur mating displays and the evolutionary driver known as 'sexual selection.'
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Since prehistoric times, males looking for mates, have driven off weaker rivals. Females, meanwhile, have chosen the most impressive male performers as consorts.
Similar sexual selection behaviours are common in mammals and birds. But until now scientists could only speculate about dinosaur mating behaviour, assuming it might be similar to that of their modern relatives, the birds.
"The scrape evidence has significant implications," Lockley said.
The study was published in the journal Scientific Reports.