Category Zoology

                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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                                A group of mammal-like reptiles preceded the appearance of the dinosaurs. However, these early mammals gradually disappeared during the Triassic Period and were replaced by the true mammals. It is difficult to decide exactly which of these extinct animals was a reptile, and which had become a mammal. It is quite likely that the later reptiles had hair and other mammal-like characteristics.

                            It has been suggested that dinosaur DNA (the substance found in all cells) might have survived in the remains of blood-sucking insects preserved in fossilized tree resin, or amber. The film Jurassic Park was based on this appealing idea. However, we have to be content with the dinosaur descendents that still exist, such as birds, because only tiny and incomplete traces of DNA have been found in this way.

Was the Earth struck from space?

There is plenty of evidence that the Earth was struck by huge comets and possibly by great stony asteroids. These objects would have devastated huge areas of the land and changed the Earth’s climate for many years. At the time of the dinosaurs’ extinction there is evidence to suggest that an asteroid or comet struck the Yucatan Peninsula in the Gulf of Mexico. It produced tidal waves and global dust clouds that shut out the Sun’s light. Large amounts of the rare element iridium have been found in rocks deposited at this time. Iridium is believed to be characteristic of comets and meteorites.

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