Brachiosaurus – the ‘Arm lizard’.
The Age of the Dinosaurs
The age of the dinosaurs is known as the Mesozoic era. This stretched from 248 to 65 million years ago. It divides into three separate time spans: the Triassic, the Jurassic and the Cretaceous. At the start of the Mesozoic era all the continents of today’s earth were joined together in one super continent – Pangaea. This was surrounded by a massive ocean called Panthalassa. These names sound quite impressive until you realise they mean ‘the whole earth’ and ‘the whole sea’. The German geophysicist Alfred Wegener first came up with the theory of moving tectonic plates, or ‘continental drift’, in 1912. He examined similarities in rocks found as far apart as Brazil and southern Africa and realised they came from a single landmass.
The Triassic world saw the first small dinosaurs, walking on their hind legs. This period lasted from 248 to 206 million years ago. Over millions of years Pangaea split into continents and drifted apart. After separation, different groups of dinosaurs evolved on each continent during the Jurassic period from 206 to 144 million years ago. This was the era of the giants. Huge herbivorous dinosaurs roamed in forests and grassland that covered entire continents.
The continental ‘plates’ are still moving today. In fact, wherever an area is prone to earthquakes or volcanoes, the cause is almost always one plate pushing against another, sometimes deep under the sea. The vast mountain ranges of the Andes and the Rockies were formed in this way.
The Cretaceous period lasted from 144 to 65 million years ago. This age included armoured plant eaters like Triceratops, browsers like Hadrosaur and huge meat eaters like the Tyrannosaurus Rex.
The seas too were filled with predators and prey that were very different from the inhabitants of today – except for sharks, oddly enough, who seem to have reached a perfect state of evolution and then stuck there for millions of years. Crocodiles are another example of a dinosaur that survived to the modern world. Modern crocodiles and alligators are smaller than their prehistoric cousins, but essentially the same animals. A crocodile from the Cretaceous period would have stretched to 49 ft (15 m)!
Tyrannosaurus – 49 ft (15 m) of ferocious predator. Note that we have no idea of the actual skin colour.
The World of the Dinosaurs
The dinosaurs’ world was hot and tropical and dinosaurs of many shapes and sizes roamed pre-historic earth. One of the most interesting things about studying dinosaurs is seeing how evolution took a different path before the slate was wiped clean in 65 million years bc. Carnivores developed into efficient killing machines, while their prey either grew faster, or more heavily armoured as the eras progressed – the original arms race, in fact. Huge herbivores could nibble leaves from tree tops as tall as a five-storey building. The largest were so immense that nothing dared attack a healthy adult, especially if they moved in herds. The herbivores must have eaten huge amounts of greenery each day to fill their massive bodies – with stones, perhaps, to grind up the food in their stomachs.
As well as the giants, the age of dinosaurs overshadowed a smaller world of predators and prey. Compsognathus was only about the size of a modern house cat. We know it ate even smaller lizards as one has been found preserved in a Compsognathus stomach cavity.
The fastest group of dinosaurs were probably the two-legged ornithomimids – the ‘ostrich mimics’. It is always difficult to guess at speed from a fossil record alone, but with longer legs than Compsognathus, they may have been able to run as quickly as a modern galloping horse. They have been found as far apart as North America and Mongolia.
Compsognathus – meaning ‘pretty jaw’.
Ornithomimids.
Carnivores and Vegetarians
During the Cretaceous period, gigantic meateaters such as Tyrannosaurus, Daspletosaurus and Tarbosaurus ruled the land. The Tyrannosaurus Rex had up to sixty teeth that were as long as knives and just as sharp. Although the T-Rex was a fierce hunter, its huge size may have prevented it from moving quickly. It is possible that it charged at and head-butted its prey to stun them, then used its short arms to grip its victims while it ate them alive – though behaviour is difficult to judge from a fossil record alone. Much of the study of dinosaurs is based on supposition and guesswork – and until time travel becomes a reality, it always will be!
The Velociraptor was made famous by the film ‘Jurassic Park’ as a smaller version of Tyrannosaurus, hunting in packs. It may have used team work to single out and attack victims. Velociraptors were certainly well equipped to kill, with sharp claws, razor-sharp teeth and agile bodies.
Velociraptor claw and toe bones.
Our experience of evolution and the modern world suggests that carnivore hunters are more intelligent than herbivores. In the modern world, for example, cows need very little intelligence to survive, while wolves and leopards are capable of far more complex behaviour. We apply the patterns we know to fill the gaps in the fossil record, but intelligence is one of those factors that are practically impossible to guess. If it were simply a matter of brain size, elephants would rule the land and whales would rule the sea.
Armour
One aspect of the age of dinosaurs that has practically vanished from ours is the use of armour for defence. It survives in tortoises, turtles and beetles, but otherwise, it has vanished as a suitable response to predators. By the end of the Mesozoic era, the arms race between predator and prey had produced some extraordinary examples of armoured herbivores. The Stegosaurus, meaning ‘covered’ or ‘roof lizard’, is one of the best-known examples and evolved in the mid to late Jurassic period, some 170 million years ago.
Stegosaurus was a huge plant eater about the length of a modern 16 sixteen-wheel truck. The plates along its back would have made it much harder for a predator to damage a Stegosaurus spine. In addition, it had a viciously spiked tail to lash out at its enemies. Some dinosaurs, like the Ankylosaurus, even had their eyelids armour-plated.
Stegosaurus
Triceratops means ‘three-horned face’ and was named by Othniel C. Marsh, an American fossil hunter. It looked armoured for both attack and defence. It weighed up to ten tons and its neck protector was a sheet of solid bone – clearly designed to prevent a biting attack on that vulnerable area. It was very common 65 to 70 million years ago in the late Cretaceous period.
The camouflage dinosaurs used is unknown. Skin just doesn’t survive the way bones do and, for all we know, some dinosaurs could have been feathered or even furred. Today’s animals leave some clues, however. Living relatives of dinosaurs such as birds and crocodiles show how some dinosaurs may have been coloured. Large plant eaters like Iguanodon probably had green scaly skin and predators
