The first animals in land

   The step from fish to amphibian' required limbs to walk with, and lungs for breathing. As a result amphibians emerged from the water, but were largely confined to the water's edge. So far as we know they laid their eggs in water, and these hatched into young with gills. Next came the reptiles, whose young also hatched from eggs. Since reptile eggs were covered with a shell they could be laid on land.

   Following on from this some reptiles gave rise to birds, and others to mammals. Both are warm-blooded animals covered in feathers or hair, but whereas birds still lay eggs, as did their reptile ancestors, mammals have progressed from egg-laying to producing living young. From the mam­mals man evolved about two million years ago. With his superior brain and skilled handiwork man now dominates the world in which, some 300 million years ago, fishes were the highest form of life.

   These early fishes included a group of so called lobe-finned fishes, to which Latimeria belongs. In the Devonian lakes lived Eusthenopteron, one of the most likely fish ancestors of the amphibians. It looked fish-like but could breathe air. By late Devonian times amphibians had developed limbs. One of these, Ichthyostega, walked on land but still had a fish-like tail supported by fin rays. Amphibians flourished during the Carboniferous or Goal Age. By the time of the Permian Period some had become giants and almost entirely land dwellers, like the two-metre (six-foot) Eryops. Of special interest is Seymouria, another land dweller, whose skeleton was part amphibian and part reptilian.

   The link between reptiles and birds is well shown in the famous fossil of archaeopteryx (the 'ancient wing'). It could well be described as a lizard in bird's clothing. It lived during the Jurassic. Earliest mammals have now been traced as far back as the Triassic. The few remains of then reveal tiny, shrew-like creatures, such as Megazostrodon.