Reptile

Reptile Evolution and Natural Selection

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Reptile Evolution and Natural Selection

Introduction

Reptiles are members of the class Sauropsida under kingdom Animalia They are tetrapods and amniotes which mean that embryos are enclosed by an amniotic membrane . Crocodilia , Sphenodontia , Squamata and Testudines are the extant species inhabiting

every continent excluding the Polar Regions , the Antarctica . Reptiles are also referred to as cold-blooded ' or ectothermic animals that rely only on the temperature changes of its environment , e .g . moving between sun and shade , for internal temperature regulation

The oldest known reptile as of 2006 is the Hylonomus which lived 315 million years ago . This organism is the precursor of modern reptiles that we know today . Sauropsids during the Carboniferous period are distinguished by having a notch at the back of the skull where jaw muscles are stacked . Most of Holynomus body systems resemble that of the existing Sauropsida species

The first two branches of Sauropsids were the subclasses Anapsida and Diapsida . Anapsids do not have holes other than the holes for the nose eyes , spinal cord , etc . Diapsids are characterized by a pair of holes located at the back of the skull . Later on , subclass Diapsida split into two lineages : lepidosaurs and archosaurs . Lepidosaurs include snakes and lizards . Archosaurs include crocodilians and birds

Evolution of Reptilian Body Systems

Reptiles were the rulers of terrestrial , aquatic and aerial ecosystems during the time when dinosaurs inhabited the planet (approximately 230 million years ago . Despite the extreme environmental conditions of the earth , reptiles managed to overcome it . Although the largest and the meanest of the reptilian kind were extinct 65 million years ago , the sheer physical strength of these creatures are still characteristics of the existing reptile species inhabiting the planet . Reptiles have astounding body systems that enable them to live in almost all environments except in places where there is too low temperature , e .g the Antarctica , as limitations of their cold-blooded ' nature

Circulatory System

Reptilian circulatory system is a closed system with the central organ the heart , having three-chambers (two atria and a ventricle . Because of this characteristic and with the help of fluid dynamics , reptiles can easily alter blood flow from the lungs to the body allowing greater control for thermoregulation or for staying longer underwater . But some reptiles are exempted from this characteristic . For instance , crocodiles have four-chambered hearts that transforms into fully functional three-chambered hearts during dives . Some snakes and lizards were also found to have the ability to transform their three-chambered hearts into functionally four-chambered hearts during contraction

Respiratory System

All reptiles have lungs which they use to breathe in any environment However , different groups of reptiles have different methods of lung ventilation . Squamata (scaled reptile , which is the existing largest of reptiles , breath through their axial musculature...