Category Zoology

                      The earliest known reptiles were small lizard-like animals, only a few centimeters long. They appeared about 330 million years ago, and are known to have lived in the rotted stumps of fallen trees. They probably fed on insects and other small creatures living in fallen trees. Reptiles quickly adapted to live in habitats that were not suitable for the amphibians. They spread across many parts of the Earth’s surface and developed into flying forms as well as many types of land-dweller.

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                     The development of eggs with protective shells was the single thing that freed reptiles from the watery environment which amphibians needed to reproduce. The egg of a reptile contains membranes, which surround the developing embryo. They provide a protective pool of liquid and food stores for use while the embryo grows. The young reptile completes its development inside the egg, and emerges perfectly formed as a miniature version of the adult.

                               Reptiles also differ in having a scaly skin that helps protect them from predators, in contrast to the thin naked skin of amphibians. Their heart and circulation is also improved to allow them to have a more active lifestyle.

                     Reptiles evolved from amphibians, but there are several important differences between these two kinds of animal. The most obvious difference in the living animals is that reptiles have scaly skin to prevent their bodies from drying out, while amphibians have thinner, moist skin. Reptiles also have a more efficient heart and kidneys to equip them for living on land, and they have evolved more efficient ways of walking. It is not so easy to tell the difference between reptiles and amphibians when examining fossils because the soft parts of the body are nut preserved. However, there are important structural changes in the skeleton that can be observed.

                      Frogs, toads, newts and salamanders are amphibians which survive today. There are also some other unusual types of amphibian, such as blind cave-dwellers. All modern amphibians produce aquatic tadpoles from their eggs, which are laid in water or kept moist by special body modifications. It is thought that their ancestors reproduced in the same way.

                     Amphibians such as frogs and toads are valuable because they eat huge amounts of damaging insect pests, but their numbers have been drastically reduced in recent years. They are sometimes used for food, and they are also susceptible to the many insecticides used by farmers.

                        As fish evolved into land-living animals, they had to change their body form. Water supports the body, but on land the animals needed to evolve a strong spine and ribs to stop their body from collapsing. They needed to develop muscles to support the body and to move the limbs. New bone structures had to evolve to support the limbs. Other changes were the perfection of lungs for breathing air, and sense organs, which would work well on land. Despite adaptations, these animals still needed to keep moist and to return to the water to breed. They are known as amphibians, which means ‘living on land and in water’.

Picture credit: google

                        Primitive fish with leg-like fins are thought to have become extinct during the period when dinosaurs lived. Later they were found, alive and well, living in the Indian Ocean. One of these fish is the coelacanth, a large fish up to 1 m long with strange leg-like fins. It was found to contain bones that were very like those of land-living vertebrate animals.

                        The first of these unknown fish was caught off the Comores Islands in the 1930s. It was later found that coelacanths were common enough to be a popular food. They have since been found in other places, always living in very deep water. Because they have hardly changed over many millions of years, coelacanths can be described as true ‘living fossils’.