Getting face to face with dinosaurs

I TOOK my grandchildren to the Dinosaur Encounter, an exhibition attracting hordes of youngsters in Dublin.

Robotic models of the giant reptiles gyrate and roar against a Jurassic backdrop.

The originals became extinct 65m years ago, yet dinosaurs capture the imaginations of children today; my grandson, Tommy, not yet three, can identify and name the commoner ones. What masters of spin the grotesque giants were. Scared but safe, like roller-coaster riders or adults watching horror movies, children wallow in delicious terror of the freakish beasts. Could there be a dinosaur living, secretly, at the bottom of the garden? Ironically, the extinct monsters also resonate at the other end of life’s journey; fuddy-duddies, like myself, are often dismissed as “dinosaurs”. Giant reptiles were the most conspicuous creatures on the planet for 150m years, an inconceivably long period. The group to which we belong, the hominids, is a mere two million years old and our species has been around for only 200,000 years. Although many dinosaurs were small, some the size of farmyard chickens, the tribe included the largest land animals ever to have lived. Brachiosaurus, the “arm lizard”, weighed up to 100 tonnes. Diplodocus, the “double beam”, resembled a suspension bridge; a ridiculously long neck was balanced by an equally long tail, the serpentine body held aloft on four pillar-like legs. Some specimens were 35m long, although they weighed a mere 10 to 16 tonnes.

Why dinosaurs grew so large has been much-debated. It’s thought that there were two main factors. One had to do with food and digestion. The menu on offer to ancient vegetarians was limited and unappetising by modern standards. Two types of plant dominated the Jurassic landscape. Cycads looked like modern palm trees, although they are not related to them, their massive trunks topped by crowns of leathery leaves. Conifers, the cone-bearing evergreens, formed the other main group. Ferns provided the ground cover. Digesting such vegetation was difficult. Dinosaurs lacked the grinding molars of modern cows and deer. They relied entirely on stomach bacteria, and corrosive acids, to break down the tough fibres. Such an operation took time; food had to be held in the stomach for long periods. This led to the evolution of great bulky organs in which food could ferment for days.

The other great challenge to dinosaurs was keeping warm. They, like modern reptiles, couldn’t heat their bodies internally; energy had to be absorbed from sunlight. Reptile body temperatures rise during the heat of the day, and drop back in the cool of the night. But the weather then, as now, was fickle. Prolonged cold periods could be threatening; animals were vulnerable to hypothermia. Big things take longer to cool down and warm up than small ones. Being very big, provided that you could get food to sustain you, improved your survival prospects during long, cold spells. With abundant vegetation to keep them fuelled up and the stomachs to deal with it, some dinosaurs became super-sized. Not all were vegetarian.

Carnivores don’t need much time to digest food; unlike those of plants, the cells of animals are not encased in cellulose. Most ancient meat-eaters scavenged for a living, but some were hunters. To bring down large plant feeders, a predator had to be big; Tyrannosaurus rex developed massive jaws lined with lethal teeth. But the monsters seem to have lost their battle with the cold. A global catastrophe, possibly the result of an asteroid impact, may have ushered in a period of partial darkness. Perhaps the sun was obscured by clouds of dust, and the dinosaurs could no longer keep warm. The fact that some of their aquatic relatives managed to survive lends credence to the theory. Primitive crocodiles were already living in the estuaries and swamps, before dinosaurs arrived on the scene, and they are still around today. So are turtles. During prolonged cold spells, the sea cools much more slowly than the land, providing a reservoir of comparative warmth during a post-asteroid winter, a lifeline for crocodiles and turtles.

Dinosaur Encounter is at the Ambassador Theatre, O’Connell Street, Dublin.