Despite their reptilian traits, mating behaviour in dinosaurs may have also made them more similar to modern birds, scientists have found.
Researchers discovered fossils of "huge scrapes" left in rocks more than 100 million years, suggesting the ancient animals may have attracted mates with "scrape ceremonies" similar to those performed by modern evolved birds.
The ceremonies, or "nest scrape displays" typically see the males of the species show off their ability to provide by digging up pseudo nests for potential partners.
The researchers at the University of Colorado Denver found evidence of more than 50 dinosaur scrapes, some as large as bathtubs, in fossils obtained across two National Conservation Areas near Delta, Colorado.
Professor Martin Lockley, a paleontologist who led the research at the University of Colorado Denver said: "These are the first sites with evidence of dinosaur mating display rituals ever discovered, and the first physical evidence of courtship behaviour.
"These huge scrape displays fill in a missing gap in our understanding of dinosaur behaviour."
He said the new evidence supports theories about the nature of dinosaur mating displays within the "sexual selection" process, which drives evolution. Throughout history, males looking for mates have driven off weaker rivals, while females have chosen the most impressive male performers as consorts.
This behaviour is common in mammals and birds so, until now, scientists could only speculate about dinosaur mating rituals and assume any similarities.
Prof Lockley said: "This is physical evidence of pre-historic foreplay that is very similar to birds today. 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 and his team created 3D images of the scrapes by layering photographs and then made rubber moulds and fibreglass copies. These are currently being stored at the Denver Museum of Nature & Science.