We’re confident dinosaurs didn't attract their mates with flowers and chocolates, but it’s hard to say for sure what DID go down. Once you look past the commercialism, Valentine’s Day boils down to the irrepressible natural forces of affection and desire. Underlying these forces is our drive to reproduce—so it may be timely to ask what we know about dinosaur reproduction.
Beyond the undeniable curiosity as to just how a pair of multi-ton Brachiosauruses might have performed the jig of life, there is some important science to be learned from dinosaur reproductive habits. Millions of years of dinosaur reproductive evolution shaped today’s birds, which are dinosaurs in the same sense that we humans are primates, and therefore, mammals.
Much as we would like to know, there’s relatively little fossil evidence about dinosaur sex. For clues, we look to birds, which descended from dinosaurs, and crocodylians, their closest living relatives. Like birds and crocodylians, we think that male dinosaurs likely engaged in visual and vocal behaviors to attract mates.
Many dinosaurs had unusual skeletal structures like plates, frills, crests, and horns that may well have been used in such display behaviors. Some of the most spectacular examples can be seen in the diversity of horned dinosaurs (Ceratopsia) from the Late Cretaceous of North America. Triceratops is but the most famous of this group of dinosaurs, with massive skulls adorned by an assortment of spikes and a huge shield extending over the neck. Many carnivorous dinosaurs had strange crests and horns over their eyes, while others bore feathers. Preserved fossil color patterns indicate that feathers may have been used in visual displays like in their living descendants, birds.
Just what such displays may have looked is largely speculative, although one set of fossil traces has been interpreted by some paleontologists as “arenas” where male carnivorous dinosaurs scraped the soil in displays like those seen in some living birds.
We have even less knowledge about how mating itself took place. We can infer that male dinosaurs would have a had penis like male crocodylians and some birds like ostriches and ducks, but just how a male Stegosaurus may have mounted his mate with all the plates and spikes in the way is still a mind-boggling mystery.