Male muscovy ducks, for example, have corkscrew-shaped penises that spring out from their body in less than half a second and are 20cm long when erect. Some ducks also have barbs on their penises to scrub away competing sperm.
So females seem to have evolved vaginas that make it hard for a male duck to actually inseminate them, if they don't want it to, by forcing it towards the dead ends.
But by looking to dinosaurs' closest living relatives – birds and crocodiles – scientists are piecing together how they reproduced.
Some people have suggested that female dinosaurs would have struggled to bear the load of males during mating.
If males did throw their leg over the female, like elephants and rhinos do today, the load would have been no more than what a female dinosaur lifting one leg up to walk experienced.
It lived around 75 million years ago, during the Cretaceous period, and was around 8 metres long.
Both birds and crocodiles have "cloacas", so it's likely that dinosaurs did too.Eagles get their cue from nature as hormonal changes occur during photoperiodism, as the days get longer after the Winter Solstice.