A Tyranosaurus rex female plays with her infants

Credit: Kevin Stead/COSMOS

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Kenneth Carpenter in his 1999 book, Eggs, Nests and Baby Dinosaurs: A Look at Dinosaur Reproduction asks, "You want to know how a pair of three-ton stegosaurus did it? Probably like porcupines: very carefully."

He suggests that 'housecat-style' could have been in the dinosaur armoury. "How stegosaurus, with the big plates on his back, managed to have sex is really not that difficult," he wrote. "With the female squatting in the front while standing on her hind legs, the male could easily rest his forelimbs on one side of her broad pelvis."

Roger Seymour is not so sure and after all, his team was the first to study mating echidna. "They do it very carefully. The female echidna rolls on to her side, as does the male who tucks its tail under the female's and they go for it for at least four hours."

They only mate once a year. So getting it right can mean the difference between life and a deadly splinter.

Modern megafauna such as the rhinoceros and elephant provide some insights, except they don't have long, thick tails to contend with. A 1991 scientific paper, entitled "Fusion of Caudal Vertebrae in Late Jurassic Sauropods", found that fusions of the tail vertebrae closest to the pelvic girdle were common among aptosaurs, diplodocus and camarasaurs. Why? Possibly, so their tails wouldn't snap off during mating.

Authors Bruce M. Rothschild, of Northeastern Ohio Universities College of Medicine in Rootstow and his colleague David Berman suspect this fusion may have occurred only in female dinosaurs that could lift and arch their tails during mating.

"This probably made sex quicker and easier," according to palaeontologist John Long, head of science at the Melbourne Museum ib Australia. A fossil fish expert, Long said the origins of sexual reproduction in vertebrates could be found in early fish such as the shark-like placoderms, in whom males had external clasping organs while females had wide pelvic plates.

Long said dinosaur eggs and nests were providing new insights into the social interaction of the giant beasts. Dinosaurs were prolific egg-layers and very protective of their young. They also built elaborate nests in grounds used seasonally by herds of different species.

But he added that because there is no fossil evidence for sexual organs, all the theories about dinosaur sex are just guesswork. He notes that some dinosaurs may well have had a penis that was tucked away when not in use - much like modern whales - but being soft tissue, we just don't know. While very little is known about the mechanics of mating in dinosaurs, Long, in his 1995 The Rise of Fishes, describes reproduction as a driving force in evolution, "paramount to the continuation of the species".

Unfortunately, that continuity was interrupted abruptly about 65 million years ago when a giant asteroid struck the Earth and wiped out anything weighing more than 25 kg. The age of the dinosaurs ended and the planet's most successful lovers took their sexual secrets with them.