The dinosaur story began over 190 million years ago when the world was simple. Just one supercontinent existed with Gondwanaland in the south and Laurasia in the north in which the lizard-like ancestors of a whole zoo of curious reptiles including the dinosaurs had evolved. The simplest name for them was thecodonts or socket toothed but that has been superceded by finer classification. These animals which had longer hind limbs than fore limbs and some probably walked on just two, were the ancestors of several lines of succesful reptiles. Moving on by a huge leap of time we can see how the movement of the Earth's massive crustal plates began to separate South America and Africa about 130 million years ago. The Andes mountains had not even begun to form and many of the species we know today had not evolved. It was an age when reptiles ruled the Earth. By about 100 million years ago the 'reptile age' was going well for the reptiles and they had evolved as many different forms of beast: some as plant eaters, some as meat eaters, some running, some in the seas, some flying and even the first bird-like creature with primitive feathers was about.

Dinosaurs were a highly successful land-living group of these ancient reptiles and they roamed over great plains. Not all the dinosaurs were large and while some reached 80 tonnes or the weight of about twenty modern day elephants, others were no more than the size of a mistle thrush. Their home was a spectacularly primitive world studded with tall trees with branching stems. These were peculiar trees with small leaves and were the ancestors of present-day pines. The scene was quite unlike anything near Sucre today.

The footprints at Cal Orko come from near the the end of the dinosaur era which was relatively abrupt at about 65 million years ago. There have been countless theories for the 'great extinction' of these extraordinary animals and it is to be hoped that on-going studies of the dinosaur traces in Bolivia may help solve the mystery

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