For years scientists have been trying to find the mysterious evolutionary master key responsible for transforming the dinosaurs into world-beaters. In the early Jurassic, 200 million years ago, they were a relatively small group of primitive creatures. By the late Jurassic, 50 million years later, they had become the magnificent array of carnivores and giant plant eaters that would dominate the planet for millions of years. In between lies the mysterious period of the middle Jurassic in which all these changes must have happened. But what were they? What was it that transformed the dinosaurs?

Was there some terrible mass extinction? Had there been an amazing change in the environment? All this was speculation and theory. How and where would evidence come to light? Fossils from the middle Jurassic are incredibly rare. All anyone had to go on were a few small outcrops of rock dotted around the world.

Then a treasure trove of fossils emerged from the midst of an Argentinian wilderness in the 1990s; thousands of square miles of mid-Jurassic rocks. On their first season in the field, paleontologist Oliver Rauhut and his team unearthed two giant meat-eating dinosaurs and six huge long-necked dinosaurs. And there was much more: early mammals, crocodiles, fish and even plant life. They had uncovered a complete mid-Jurassic eco-system, a wonderful snapshot of life from this dark age of dinosaurs.

"It's as if someone has unearthed a holy grail of dinosaur palaeontology," says British geologist, Dr Phil Manning. Oliver Rauhut describes the site as, "an extraordinary window on the mid-Jurassic." Above all, the hope is that this site may contain all the information they need to find the mysterious evolutionary forces that have eluded palaeontologists for so long.