Category Zoology

                       Among the earliest large inhabitants of the seas and shallow waters were giant relatives of the scorpions and spiders. Some of these creatures were around 10 cm in length, but others were enormous — up to 2 m long. These fearsome creatures had a flattened armoured body, and claws tipped with sharp spines for catching their prey. As well as ordinary jointed walking legs, they had large paddle-shaped limbs with which they rowed themselves along. They could swim by beating their tails up and down. These creatures were the largest predators living in the seas 450 million years ago.

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                     Trilobites are another of the great groups of animals that lived 500 million years ago, but have now disappeared. They looked rather like large flattened woodlice (pill bugs). Some trilobites were predators, but most were scavengers that scuttled around on the sea-bed on their many jointed legs. Some grew to a length of 45 cm and weighed about 4.5 kg, but most were much smaller. Like woodlice, trilobites could roll up into a ball when threatened. The name ‘trilobite’ comes from the animal’s appearance — its body was in three lobes. Trilobites were arthropods (animals with jointed skeletons), and like modern crabs and lobsters they had to split their rigid shell and emerge before they could grow bigger.

Ammonites were members of the same class of animals as the modern octopus and squid. They were tentacle animals that lived in a flat coiled shell. There were many thousands of different types of ammonite. The shells of some ammonites were as much as 1 m across, but most were much smaller. The animal lived in a small horny cell, constructing a new cell as it grew. The cells contained gas, probably making the shell buoyant and allowing the animal to swim freely. Later, the shells of some ammonites became partly straightened out. Ammonite shells have been well fossilized. They are commonly found on beaches, where they have been washed out of the soft rock by wave action.

                 Animals such as fish, amphibians, reptiles, birds and mammals have a backbone. It supports their body and serves as an anchorage for the muscles. These animals are called vertebrates. Some of the ancestors of vertebrates are found in old fossils. They have traces of a stiffening rod to support their back, which is thought to have later evolved into a proper spine.

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                 Evolution seems to have carried out some very strange experiments. Some of the earliest forms of animal life did not lead to further evolution, so they died out quickly. A few creatures have survived almost entirely unchanged, such as brachiopods. These look like small clams although they are unrelated. They appear in the oldest fossil beds and survive in exactly the same form to this day, living in ocean depths.

                 Some of the oddest failures in evolution were found in a layer of rock called the Burgess Shale, in Canada. This rock preserved the tiny remains of soft-bodied animals, which is an extremely rare occurrence. The animals amazed scientists because most of them had no relationship to any other known life form.

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                   The fossil record has very large gaps in it, so there are periods where we know little about the life that once existed. Conditions may have changed long ago, making it unlikely that fossils were preserved. Also, changes on the Earth’s surface may have worn away rocks that contained fossils.

                 Fossil shells are quite common, but fossils of larger animals are very rare. It is even more unusual to find a complete skeleton of an animal such as a dinosaur, because its carcass would have been partly eaten by scavengers and the remains scattered. Some of the best fossils were formed in shallow lakes or mudflats, where the animal has been preserved because it was quickly covered with protective silt. Preservation of a delicate animal in fossil form requires ideal conditions, such as soft mud where there is no oxygen present, so scavengers cannot destroy the carcass.