Flexible stegosaurus found inventive way to mate to avoid partner's spiky back Dinosaurs with spiky backs mated in the missionary position, a study reveals Spikes risked injuring the male if they mated like other animals Dinosaurs with spiky backs or tails may have had sex in the missionary position to prevent them from being castrated. A new study has revealed that some species adopted the position to avoid the potentially lethal spikes on the rears of the females. It contradicts long-held beliefs that all dinosaurs mated in the same way - with the male mounting the female from behind. Dinosaurs may have had sex in the missionary position to prevent them from being castrated, according to a new study. Researchers argued that for species like the stegosaurus, which had a stiff, spiky tail, the position could have proved dangerous or even fatal. Brian Switek, a dinosaur expert, said: 'The females could not raise their tails because the bones at the top end were fused. Also, some species had lethal spikes on their backs, which would have been impossible to get past. Heinrich Mallison, a scientist at the Museum of Natural History in Berlin, tested out the theory by designing computer models of kentrosaurus, a cousin of stegosaurus. Using the software, he found that males would have 'risked castration' from the deadly spikes on the female's hips if they tried to mount from behind. Some species would have mated in the missionary position to avoid the lethal spikes on the rears of females He said: 'These prickly dinosaurs must have had sex another way. Perhaps the female lay down on her side and the male reared up to rest his torso over her. Other species would have used different positions, like backing up to each other. Experts say understanding such adaptability is key to working out how the animals were able to dominate the Earth for tens of millions of years. But some scientists disagree with the theory, suggesting that male dinosaurs continued to mount the female but developed extremely long sex organs. These may have grown several feet long so they could reach around any dangerous spikes - a tactic still seen in animals such as armadillos. John Long, professor of paleontology at Flinders University, Australia, told the Sunday Times: 'A 33ft-long ankylosaurus with spikes and armour would have a 6ft penis to bridge the gap when he got close to a female.' It is thought the only way to resolve the issue is through fossil evidence - but chances of finding this are slim. Mr Switek said: 'Soft tissues are seldom preserved during fossilisation, so we have never found a fossilised phallus, but doing so would solve many mysteries.'