My Science School

Most modern museums are very different from the early scientific exhibits of the 1800s. This was the time when popular interest in prehistoric life grew, and fossils of dinosaurs and other extinct creatures were first put on display to the public.

Today there are thousands of exhibits in natural history museums. Scientists have been able to reconstruct, in painstaking detail, how prehistoric creatures would have looked in real life. This gives us important information about the probable habits of these animals, instead of simply showing a mounted skeleton or fossil.

Wherever you live, take the time to look at the fossil remains in your nearest museum. By using your imagination, try to picture these extinct creatures as they once would have roamed the Earth.

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                       Some fossil footprints of Apatosaurus caused puzzlement when scientists realized that they were the imprints of only the front legs of this vast reptile. They realized that the Apatosaurus must have been wading along in shallow water, pushing itself along with its long front legs while its hind legs floated clear of the muddy bottom.

                     At one time scientists thought that sauropods were far too large to have walked on land, and that they must have lived entirely in swamps where the water would support their weight. We now know this is incorrect, and that these giants were normally land-dwellers. In fact, they would probably have become stuck in soft mud due to their enormous weight, and preferred to live on dry land.

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Fossils are usually first revealed by the process of erosion, or by quarrying. They are found in sedimentary rocks which have been formed from mud and sand laid down millions of years ago. The remains of animals and plants are buried in the layers of rock. These sedimentary rocks are often buried deep beneath layers of other rocks that do not contain fossils. They are often exposed in sea cliffs, where the rock is worn away by the waves. Mining and quarrying also expose the deeper layers of rock, and many fossils are found in the loose material at the foot of rock faces.

Where are most dinosaurs discovered?

Most fossils have been found in Europe and North America, but they have also been found in most other parts of the world. In recent years, huge numbers of new and exciting fossils have been discovered in China, including huge new sauropods and several of the small dinosaurs which seem to have given rise to modern birds.

Fossils of mammals are not so old as those of the dinosaurs, and they are found in other regions. In particular, fossils of early man and the ancestors of mankind have been found in Africa.

 

Could we ever reconstruct an extinct animal?

We know that it is very unlikely that a dinosaur can be brought to life because its DNA is no longer complete. However, there are other possible ways of re-creating more recent animals.

Woolly mammoths are often found buried in the permanently frozen ground of Siberia and Alaska, and attempts have been made to extract DNA from the carcasses. It is hoped that this material could be inserted into the egg cells of a modern elephant, so a mammoth could be born again.

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Many people must have noticed old bones in the ground, but they did not attract much attention. In the 1500s dinosaur fossils were thought to be the remains of animals or human giants that had perished in the Biblical flood.

The first proper scientific investigation took place after a huge pair of jaws was unearthed in the Netherlands in 1770. The jaws were identified by the great anatomist Cuvier, who recognized them as the remains of a marine lizard. The creature was christened ‘Mosaurus’. Many other fossil finds followed, and by 1830 five major groups of extinct reptiles had been recognized.

Why do palaeontologists disagree about dinosaurs?

Scientists have found very few examples of some of the more interesting and puzzling types of dinosaur. It is very rare to find a complete skeleton, and even rarer to find other clues, such as the animal’s last meal or traces of its fur or feathers.

As a result, palaeontologists often guess at the appearance of an extinct animal, based on a few clues and on similar living animals. This method leads to strong disagreements. For example, some experts say that dinosaurs must have been warm-blooded, in order to move quickly and to live in such varied habitats. Others insist that they were cold-blooded animals, like modern reptiles.

How are dinosaurs preserved and reconstructed?

It is rare that you can just pick up dinosaur bones. They are usually embedded in very hard rock, and it can take weeks of painstaking work to chip them out carefully and release the whole skeleton. Usually the bones were scattered before fossilization, so palaeontologists often have to excavate a wide area around the first finds in order to make sure that they have not missed any important parts. The remains may be taken to a museum still embedded in a block of stone. Once the rock is removed, the fossil bones are reconstructed on a metal frame. These bones have now turned to stone and so they are very heavy and brittle. As a result many museums make castings of the bone in plastic, which can then be jointed together for display.

 

 

Dogs appear to have evolved from small mammals such as the mongoose, which appeared about 30 million years ago. This family proved very successful, and even the very early forms were similar to the modern dog. The early animals probably hunted in packs like modern animals of this group, enabling them to bring down large prey.

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                        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.

 

 

 

                This odd creature looked very much like some of the dinosaurs. It was a giant armadillo-like animal, with a shell 1.5 m long. Its head was covered with armoured plates, and the tail was also armoured. In many types, the tail was tipped with a huge bony club or massive spikes which the creature could swing to defend itself.

 

 

                           Sabre-tooth cats survived until as recently as 10,000 years ago, and must have been encountered by prehistoric humans. The best known of these cats was Smilodon, which was more massive than a lion. It had a pair of canine teeth up to 20 cm long. It used these teeth to slash and stab its prey, and it could open its jaw very wide to allow the teeth to be used in this way. Smilodon probably brought its prey down using its considerable weight and sharp claws, before stabbing with its enormous teeth.

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                      Marsupials, like the kangaroo, are said to be primitive mammals because they give birth to tiny undeveloped young. The young are raised in a pouch until they are developed enough to live on their own. Two surviving kinds of mammal, however, still lay eggs like their reptile ancestors. Both the duck-billed platypus and the spiny anteater, or echidna, lives in Australia. They lay eggs, and the hatchlings are placed in a primitive pouch on the mother’s stomach. Unlike the young of reptiles, these babies are nourished with their mother’s milk. These two peculiar animals give us some indication about how the earliest mammals may have developed.

What are placental animals?

                 Placental mammals give birth to well-developed young, unlike the marsupials. These animals are called placental mammals because their babies are nourished inside the mother’s body by a large fleshy organ called the placenta. It extracts food and oxygen from the mother’s blood and passes it to the developing young, removing waste products at the same time.

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                             The first mammals were small and inconspicuous, and they were vulnerable to all the fierce dinosaur predators. Once the dinosaurs died out, the mammals were able to develop and evolve. Eventually the mammals grew into forms that were almost as gigantic as their dinosaur predecessors. Indricotherium, which was a member of the rhinoceros family, developed into something resembling the giant sauropods but with a shorter neck and tail. It grew to a height of 5 m at the shoulder and weighed 15 tonnes. It probably grazed on trees, like the modern giraffe. Indricotherium had four large teeth, two in the upper and two in the lower jaw. It also had three toes on each foot. In many ways it resembled a gigantic tapir.

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