1. Male Pelecanimimus dinos apparently liked to hitch a ride on females during sex. Jose Antonio Penas/Science Photo Library The ostrich-like Pelecanimimus dinosaur lived around 120 million years ago, during the Cretaceous period, and was 2 metres from head to tail.Historically, scientists have sidestepped the issue of dinosaur sex, both because there was a bit of a taboo around studying it and there wasn't much evidence. Sadly, no fossils have (yet) been found of dinosaurs actually having sex, and even the best preserved fossils don't show the dinosaur's reproductive system. But by looking to dinosaurs' closest living relatives – birds and crocodiles – scientists are piecing together how they reproduced. This artist's impressions show what mating dinosaurs might have looked like, based on the little evidence that does exist (with a bit of artistic license thrown in). 2. Careful where you point those horns, Pentaceratops. Jose Antonio Penas/Science Photo Library Pentaceratops was a herbivore with five horns on its head and a large bony frill extending backwards from its head. 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. Cloacas are one opening that deals with intestinal, reproductive, and urinary tracts. In most early bird species, males had a penis that only emerged from the cloaca to deliver sperm when they had sex. So dinos probably did too. 3. Tyrannosaurus rex might have had a bit of a nuzzle before getting down to it. Jose Antonio Penas/Science Photo Library T. rex was one of the largest carnivorous dinosaurs, measuring 5 metres tall and weighing 7 tonnes. It lived in North America and Asia between 85 and 65 million years ago. A predator and scavenger, T. rex had the strongest bite of any dinosaur, with teeth that could penetrate bone. Bad news for lady T. rex. 4. Their tiny arms apparently didn't pose a problem. Jose Antonio Penas/Science Photo Library But for another dinosaur – a Stegosaurs cousin known as Kentrosaurus – certain body parts did get in the way. Kentrosaurus had spiky plates on its lower back and hips. Science writer Brian Switek asked paleontologist Heinrich Mallison to use a computer simulation he developed to work out whether Kentrosaurus would have been able to mate in the traditional male-putting-his-leg-over the female way. The result was not pretty. "If a male tried to throw his leg over the back of a crouching female, he would castrate himself on her sharp spikes," Switek says in his book My Beloved Brontosaurus. 5. Sauroposeidon might have done it in the water. Jose Antonio Penas/Science Photo Library This sauropod dinosaur lived around 110 million years ago. It may have the longest neck of any dinosaur, reaching up to 12 metres. This dinosaur, which was herbivorous like all sauropods, lived on the shores of what is now the Gulf of Mexico. And also had sex there. With its ridiculously long neck thrown back like this (maybe).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. In the words of biomechanics expert R. McNeill Alexander: "If dinosaurs were strong enough to walk, they were strong enough to copulate." 6. Bonus: T. rex skeleton casts in a mating position, looking at a picture of two T. rex having sex. Mario Modesto / Via en.wikipedia.org Yes, they're basically looking at dinosaur porn. Well done, Jurassic Museum of Asturias. For more on what little we know about dinosaur sex (and more) see My Beloved Brontosaurus by Brian Switek.