Category Zoology

                        Several Ice Ages occurred as the world’s climate changed and glaciers moved away from the North and South Poles. Many animals migrated to warmer climates or simply died out, but others adapted to live in this new and cooler climate. Woolly rhinoceroses and woolly mammoths appeared. They were able to survive in cold climates, as did great cave bears, hyenas and many other animals.

                          After the death of the dinosaurs, and before the development of large mammals, birds were the main predators. Some of these were fearsome, and very similar to some of the dinosaurs they replaced. Diatryma stood 3 m tall, with massive legs and talons. It was flightless, with the lightweight bones of a bird. These allowed it to run and to manoeuvre itself quickly. With its huge slashing beak it would have been able to tackle prey such as the ancestors of modern horses. These birds died out when the first predatory mammals appeared. These small fast mammals probably ate the eggs and chicks of this flightless monster, which was obliged to nest on the ground and would have been very vulnerable.

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                  Modern sloths are all slow-moving tree dwellers, but some of their ancestors were very different. Ancient ground sloths grew to an enormous size. They had a massive body, a short tail and a small head, and some grew to a length of 7 m. Their forearms were massive and had very large claws, which the sloths used to pull down the branches on which they fed. The back legs were short, and it is thought that these animals propped themselves up on their muscular tail while feeding from trees. They would have been strong enough to push over most trees.

                Giant sloths survived in the Americas until approximately 10,000 years ago. Pieces of their skin, which have been found preserved in dry caves, show that the sloths’ skeleton contained extremely tough nodules of bone. It is this bone which probably helped to protect these giant creatures from predators.

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             Whales evolved from sea lion-like ancestors that returned to the sea. We do not know what the whale’s land-dwelling ancestors looked like. Early whales were mostly like huge dolphins or killer whales. One of these, called Basilosaurus, was a slender predator about 21 m long.

            Fossil remains of whales are very scarce and not much is known about these animals. The early forms did not have the echo-sounding ability of modern whales and dolphins, which did not evolve until much later.

                They are thought to have swum with an eel-like motion and may not have propelled themselves with the flattened fluke found in modern whales. Some early whales still had rudimentary hind legs, but these were so small that they could not have played any part in swimming. When whales die their remains usually sink in deep water where they are unlikely to form fossils.

                        Animals with hooves carry all their  weight on the middle toe of the foot. This was not always the case, however. The evolution of horses shows how they changed from five-toed creatures to single-hoofed animals. Early relatives of the horse were about 30 cm tall and lightly built for fast running. There were four toes on the hind legs and three on the front legs; each toe had a small hoof. As horses grew larger, the number of toes gradually reduced until Merychippus appeared some 23 million years ago. It had several toes but carried all its weight on the large central toe, which had a hoof. Merychippus stood about 1 m high at the shoulder, and looked like a small horse. The development of the horse from its primitive ancestors is one of the best examples of evolution, because unlike many other animals, the development of the modern horse and its specialized hoofs can be seen in detail in the fossil record.

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                Although it was related to the horse and the rhinoceros, Chalicotherium was a very strange-looking beast. Its body was something like a horse’s, but its front legs were very long and powerful and were armed with large claws. It probably used these claws to dig up roots from the ground on which it fed.