A film on reptiles and amphibians would not be complete without an appearance from the most formidable reptiles that have ever lived, the dinosaurs. We decided to raise the thorny question of whether they were indeed warm or cold-blooded - a debate which has occupied the minds of palaeontologists, and anatomists for decades.
So we went to Colorado, armed with an 18-foot cardboard T. rex, a massive cherry picker and a strange silver ball. Rising on the crane to where T. rex's head would be, David held out a life-size replica of a T. rex jaw, dropped it and stood back.
On location, local palaeontologists caught the plummeting jaw in a blanket, but back in the graphics studio, computer magic held it suspended in the air and a life size, breathing T. rex grew in its place. As for the silver ball, that was used to work out the correct angle of light and shadow needed to make the T. rex look natural in its canyonland setting.
All these techniques have enabled us to capture extraordinary and previously unseen behaviour in intimate detail, overturning the myth that cold-blooded life is slow, solitary, cold and primitive and revealing these creatures to be as dramatic, social, warm, sophisticated and passionate as any other animals.