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Great Environmental Adaptations of Reptiles

© Janat Khatoon

The Class Reptilia is represented in the present time by tootsies, turtles, lizards, snakes, crocodiles, sphenodon, and others. The reptiles flourished and were dominant throughout the Mesozoic period, and others. Towards the end of the Mesozoic period a profound change, especially with regard to climate is supposed to have occurred, which affected, their population and apparently led to their decline or their evolution to birds and mammals. It is probable that colder conditions develop all over the earth surface, as a result of which the reptiles were forced to become warm-blooded or perish. It is believed that modern reptiles are the descendants of those who lived in tropical zones and survived.

The reptiles the cold-blooded (poikilothermal) vertebrates with the scaly skin. The scales are horny, epidermal structures, modified in different ways. The skin is normally dry, and the cutaneous glands are only confined to definite places. Reptilia are essentially tertrapods, typically with five clawed digits, but great modifications occur in this respect. The endoskeleton is well ossified and there is one occipital condyle in the skill. The heart is imperfectly four chambered with a right and left aortic arches; the red blood corpuscles are nucleated. Respiration takes place by lunge; functional gills are not developed at any stage of development during the life history. The eggs are large with much yolk, and fertilization is internal.

Because of these three extraembryonic membranes, oviparous reptiles were able and, indeed, forced, to lay their eggs on land. The young hatch fully formed, without a larval stage, ready to seek their own food. Not only were reptiles liberated from returning to water to lay their eggs; aquatic oviparous species must go onto land to do so, since porous eggs would become water-logged in an aqueous environment.

Reptiles exhibit other adaptations to terrestrial life. The body surface is covered with a thick layer of cornified epidermal cells that is organized into plaques, shields, or surface scales unlike the bony dermal scales of fishes and early amphibians. The scales are impervious to water, which results in water conservation, a necessity for animals living in air and often remote from water. Reptiles have developed a neck by specialization of several postcranial vertebrae. This modification combined with their single occipital condyle, enables reptiles to scan the horizon. The pelvic girdle now articulates with two sacral vertebrae, providing a stouter brace for more powerful hind limbs. The digits are supplied with claws, and a new kidney, the metanephros, has come into existence as a modification of the amphibian kidney. The heart is partially or completely divided into right and left chambers, thereby separating the systemic and pulmonary circulations to an extent not achieved in anamniotes.

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