London: With all that bony armour and spiky tails thrashing about, sex must have been a risky business for dinosaurs, which ruled the Earth for 135million years, according to scientists.
For most animals, the male mounts the female from behind.
But, according to scientists, this would be hard for creatures weighing up to 25 tons and surely impossible for the likes of stegosaurus, with its stiff, spiky tail, the Sun reported.
The females could not raise their tails because the bones at the top end were fused, said Dinosaur expert Brian Switek, whose book My Beloved Brontosaurus is out in May.
And some species had lethal spikes on their backs that would have been impossible to get past, he said.
To shed light on their sex life, Heinrich Mallison of Berlin`s Museum Of Natural History has designed computer programs modelling how dinosaurs made out.
He found that the males of many species would risk CASTRATION if they ever tried to mount their females from behind.
These prickly dinosaurs must have had sex another way, he said. 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, he stated.
According to Switek, the Dino Sutra may have had four main positions.
Rear mounting, as most mammals do today would be suitable for some lighter dinosaurs and those without spikes on their backs, such as the velociraptor.
For example, a safety-first side-on method would have avoided swipes by a stray tail for a stegosaurus.
A tricky rear-to-rear technique could be possible for the kentrosaurus if the male could swivel his neck to see where he was aiming.
And some females may have rolled on to their backs for missionary-style coupling. Tyrannosaurus rex may have mated this way.
However, not all experts agree with Switek.
Some suggested that the dinosaurs` secret was to develop massively long penises.
Prof John Long of South Australia`s Flinders University believe that a 33ft-long ankylosaurus, with spikes and armour, would have had a 6FT 6IN penis to bridge the gap when close to a female.
But it is difficult to find evidence for this theory, as the fossil record is very poor when it comes to penises.
"Soft tissues are seldom preserved during fossilisation. We have never found a fossilised phallus. Doing so would solve many mysteries," said Prof Long.