The Rise of the Dinosaurs

Of all the prehistoric animals that ever lived, the dinosaurs are undoubtedly the most famous and best known. They are also the most misunderstood.

The name 'dinosaur', which means "mighty or terrible lizard", was given to them early in the nineteenth century. In fact, although some dinosaurs were fierce carnivores, others were harmless plant-eaters and many were no larger than a domestic chicken.

Corythosaurus

The archosaurs

Where did the dinosaurs come from? We saw earlier how there was a group of reptiles, now totally extinct, the mammal-like reptiles. They reached their peak in the late Permian, giving rise to the mammals in the second half of the Triassic. Meanwhile, just as they were doing this, there evolved another great group of reptiles - the archosaurs or 'ancient lizards'. The archosaurs soon replaced the mammal-like reptiles entirely.

Shansisuchus

One of the first archosaurs was shansisuchus, which was found in the early Triassic deposits of China. It was about 4 metres long with a powerful head and neck and sharp teeth. Like most other archosaurs, the back legs of shansisuchus were longer than the front ones.

The archosaurs were to go on to become the ancestors not only of the dinosaurs but also a group of flying reptiles called the pterosaurs, as well as crocodiles and birds. The archosaurs' teeth were more or less the same in all parts of the jaws, being sharp-pointed and curved slightly inwards. They were obviously used for gripping live prey before swallowing, and also for slicing flesh.

Shansisuchus, an ancestor of the dinosaurs

Two-legged running

Like some present-day lizards, many archosaurs could use their long heavy tails to balance their body and could run about on their hind limbs. One of the earliest members of the group to do this was euparkeria, which is found as a fossil in the lower Triassic of South Africa. Euparkeria probably walked on all fours, but when in a hurry got up on its long strong hind limbs and ran.

Ornithosuchus from the upper Triassic of Scotland was rather larger and more advanced in its two-legged method of running. Its forelegs were too small to be of use in walking, while the thighs were nearly vertical. This suggests that ornithosuchus walked permanently on its hind legs.

Elbows directed backwards

Unlike the primitive reptiles and amphibians, and more like mammals, dinosaurs had their legs underneath the body, with the elbows directed backwards and the knees forwards. Thus they could stand, walk or run fast with far less effort. Dinosaurs probably also had keener senses of smell, sight and hearing, and though we know nothing of the way their muscles and blood systems worked, they were probably adapted for greater activity. Some palaeontologists believe that dinosaurs may have been able to regulate their body temperature to some extent.