The amphibians were able to survive on land as well as in water, which as we have seen, was of considerable advantage during the arid climates of Devonian times. Nevertheless, all amphibians, even those that survive today, must return to water to breed.
In fact, after the amphibians had developed, and seemed to have come to terms with their new way of life, there was a mass return to the sea, and few amphibians still exist. The early amphibians were large, being as much as two meters long, but gradually they became smaller and more variable in appearance.
The amphibians that returned to the sea had limbs and not fin like the fishes. The body become much longer and most species of the newly returned marine forms became predatory, that is, they hunted other animals for food.
A new group of animals evolved in the late Carboniferous times, some members of which were to dominate the Earth for a considerable period of time. This new group is the reptiles. Landforms perfected their means of moving in their dry surroundings by increasing the strength of the limbs.
By the end of carboniferous times, drier conditions once more came to the Earth. Thus, those species which were better able to cope with these conditions survived while many became extinct. The reptiles developed an extra outside layer to prevent the body from drying out, and eventually, a means of protecting the delicate egg was found.
Reptiles’ bodies became covered with hard plates, and these are well shown in today’s relics of the past, the crocodiles, and alligators, for example. It is possible that the protected egg, capable of withstanding dry conditions, came first as a protective adaptation for one group of amphibians, but this is not certain and there is much speculation about these early amphibians and reptiles.
During Permian times where dry conditions were very widespread and, deserts were far greater in number and extent than they are today there was a very rapid evolution, in which all the various habitats were occupied. It is worth mention here that at the same time a group of warm-blooded animals was also beginning to evolve-the mammals. It would be some times, however, before they would be as powerful as they are today.
There were also mammal-like reptiles, and in some areas, such as South Africa, these were the dominant species. Instead of the flat scales of the reptiles, he mammal-like reptiles had fine scales standing at an angle form the body and which would eventually become hair.
Hair acts as a better insulation against heat loss, so that they could live in cooler climates and eventually develop a warm blood stream so that there would be no need to hibernate during winter. But for 100 million years the reptiles were dominant, and one group, he dinosaurs, were the unchallenged masters of the Earth.
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