A book on dinosaurs about to be released gives a clue how the extinct creature had sex given their physical feature such as spiky tails and bony armours.

Brian Switek, a dinosaur expert and author of the upcoming book titled My Beloved Brontosaurus, said that the dinosaurs then mated very carefully. In human sexual position, they engaged in the so-called missionary position where the male entered and penetrated the female from behind.

"The females could not raise their tails because the bones at the top end were fused," Mr Switek explained.

To provide a more graphic idea of dinosaur sex, Museum of Natural History scientist Heinrich Mallison came up with computer models of the kentosaurus, a cousin of the stegosaurus, to find out if there was a risk to the male dinosaur every time he had sex with the female. If he mounted the female as most animals do, he was risking castration from the deadly spikes found on the hips of the female.

He theorized that the female probably lay down on her side and the male reared up by resting his torso over her.

Although discovering the Kamasutra, dinosaurs' version, may seem unimportant now, the experts such understanding their adaptability would provide the present generation an idea how these large creatures dominated Earth for millions of years.

However, other scientists believe the male dinosaur mounted the female because of their extremely long sex organs which could have reached several feet long, allowing them to penetrate without being pierced by the female's fatal spikes. Such strategies are still being used by armadillos.

Flinders University Paleontology Professor John Long believes that the 33-foot-long ankylosaurus which had spikes and armour probably had a 6 feet penis. However, Mr Switek said chances of finding evidence of that large dinosaur penis are small because soft tissues are not preserved during the fossilization. However, if such type of a phallus would be unearthed, it would solve many dinosaur mysteries that remain.