Adaptive features of Reptiles that helped them to be the first true terrestrial animals

Reptiles are a group a cold blooded, creeping animals, successfully adapted for land life. Though amphibious are considered as first land animals, reptiles are first successful animals independent of water. They do not fear of dehydration. Their success is mainly because, they lay eggs on land. They are the first member of the amniotes originated on the earth.

                Reptiles originated about 255 million years ago in the carboniferous period of paleozoic era. Reptiles evolved from Anthracosaurs of Labyrinthodonts amphibious.

                During the origin of reptiles from amphibious the following evolutionary changes has occurred that helped them to be the first true terrestrial animals on this earth.

1.       Land life: Reptiles become completely terrestrial because they did not depend on water for completing their life cycle. They were well protected from the danger of dehydration.

 

2.       Land eggs: Amphibious layed their eggs in water and they depending on water for completing their life cycle. Reptiles layed their eggs on land. This eggs were called land eggs, amniotic or cledoic eggs. These eggs were protected by an outer hard calcareous shell. The embryo developing in the shell was surrounded by a membrane called amnion which was not found in the eggs of the amphibious. Hence the reptiles eggs are called amniotic eggs. The amnion enclosed in a cavity called amnion cavity filled with a fluid called amniotic fluid. The amniotic fluid is described as the artificial swimming pool of the embryo. Hence the reptilian eggs did not depend on water for development and could develop without any problem in an completely terrestrial environment.

 

 

3.       Internal fertilization: In case of amphibious fertilization was external and this was possible because they bread in water. Reptiles started breading on lands with the help of their cledoic eggs. Hence fertilization become internal.

 

4.       Heart: To spend life on land reptiles exhibited greater activity resulting in better separation of oxygenated and deoxygenated blood stream. Hence the ventricle become incompletely separated to keep the two streams separated as far as possible.

5.       Respiration: Reptiles did not breath by gill at any stage of their life. Cuteneous and gill respirations in amphibious were replaced by complete pulmonary respiration that helped them to lead perfect terrestrial life.

 

6.       Skin: In amphibious, skin was thin and moist to help them to cuteneous respiration and this was possible because they spent a part of their life cycle in water to prevent dessication. When reptiles become terrestrial, their skin become thick, rough, non-glandular and covered with scales and shields to protect them against dessication in the harsh terrestrial environment.