A Tyranosaurus rex female plays with her infants

Credit: Kevin Stead/COSMOS

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In an article in February 1988, the (now defunct) U.S. science magaaine Omni dedicated several pages to examining the plausibility of Halstead's view of dinosaur sex. In it, he said the ancient animals were hampered by what palaeontologists called the 'golden rule': rear-mounting males always had to keep one foot on the ground to avoid crushing their mates.

"Their mating had to be done with great delicacy and great precision. It must have been utterly charming to watch, quite unlike our own species."

Halstead's article, which was illustrated by wildlife artists Sandy Fritz and Ron Embleton, entertained the idea that if dinosaurs "humped like birds, they'd have to have got past that thick, powerful tail; and for that they would need a corkscrew-shaped penis about three metres long.

"Yet there is no evidence they had such a grandiose organ," Halstead explained. "Maybe they lay side to side, male to port and female to starboard, and sort of snuggled up together, bottom to bottom."

That is the position Roger Seymour, professor in the department of environmental biology at the University of Adelaide in South Australia, is betting on. "I cannot direct you to any evidence of how dinosaurs did it," he said. "It is only recently we have learnt how to determine the sex of dinosaur fossils."

Seymour said without soft body parts to confirm dinosaurs even had cloacas, it was difficult to speculate accurately about how dinosaurs mated: "Nor do we have a set of six footprints to work from."

But whether ankylosaur or armadillo, all cumbersome lovers had to follow basic physical laws.

In 1994, during a 15-minute presentation called, "Love's Labours Lost: Mating in Large Dinosaurs", Stuart O. Landry Jr, emeritus professor of biology at the State University of New York in Binghamton, told delegates attending an international conference of vertebrate morphologists at the University of Chicago that dinosaurs must have found non-standing positions to ensure a smooth exchange of gametes.

Having turned to the sex life of dinosaurs after the American Museum of Natural History in New York produced a poster depicting a rearing dinosaur defending its young, Landry believed big dinosaurs did it like crocodiles, in water or mud, to achieve the closest thing to weightless sex. He said the image of a giant dinosaur rearing up on two legs was highly unlikely. The heart would not be able to pump enough blood that far uphill to supply the brain.

Roger Seymour agreed. "If you calculate the vertical distance between where the heart is and where the head is - and some of these animals grew to up to 9 metres - you can measure accurately what the minimum pressure is at the bottom of a 9-metre column of blood. It works out to be seven times the normal mammalian blood pressure.

"Rear mounting is not a big problem if one keeps the neck horizontal," he said, referring to recent studies of the lanky giraffe, whose blood pressure has been calculated to be about twice that of other mammals and whose hearts are proportionately 75 per cent larger.

Though water seems be the best medium in which big dinosaurs could mate without being crushed to death, what of terrestrial lovers? Stegosaurs and triceratops had more to worry about because they were covered in a lot of pointy bits, spikes and armour to ward off attackers.