After the Amphibians – What next?

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.

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Hylonomus, one of the earliest known reptiles.

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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