The reptilia are also known as creeping vertebrates. They are cold blooded. They have epidermal scales with rough and dry skin. They do not have any glands. They have 24 cranial nerves. The skull has condyle which is single and has a vertebral column. The respiration is also supported by skin and buccopharyngeal cavity. Their heart is 3 chambered with a couple of auricles and a single ventricle. It is 4 chambered in the crocodiles with 2 auricles and 2 ventricles. The renal system is not fully developed. The process of excretion and respiration occurs by a pair of kidneys which are metanephric and ribs along with the lungs respectively. They have the internal mode of fertilization. The development is direct without the formation of larva. They also show sexual dimorphism. The embryonic membranes do occur. They have a cloaca. There are 4 pentadactyl limbs and have a 5 digit claws. They have a urinary bladder. The crocodiles excrete ammonia and turtles excrete a urea. The lizards excrete a uric acid. The ear is divided into three parts which are known as external, middle and internal parts. They are oviparous and have the embryonic membranes. They do not have a well developed lateral line system.
The living reptiles are divided into anapsida and diapsida. The anapsida organisms have skull like bony roof. It has no temporal vacuities. It includes turtles, tortoises etc. The diapsida organisms have a couple of temporal vacuities. It includes sphenodones, lizards, snakes and crocodiles.
The dinosaurs are also known as ancient reptiles. They are the connecting link between a bird and reptile. They have a bird like pelvis as well as reptile like pelvis. The reptile like dinosaurs is known as Saurischia. They are fast and carnivorous. They have two legs. They also include the giant forms. They are known as tyrannosaurs. They are around 15m long. They can also eat plants. They also have 4 legs. The largest form of this type is known as the brachiosaurus. The bird like dinosaurs is known as Ornithischia. They are herbivorous and are 4 legged. They have an upright movement. They do not have teeth and are stout. They have a bird like beak. It includes the ankylosaurus in this group.
The embryo forms 4 membranes known as the embryonic membrane. It occurs in the reptiles, birds and mammals. These include chorion, amnion, allantois and yolk sac. These organisms are known as amniotes. There are the organisms without these membrane and are known as anamniotes. It includes the fishes and amphibians.
The chorion protects the embryo. It also takes part in the formation of placenta. The amnion forms sac which is filled with the fluid and protects from the shock and desiccation. The allantois arises from the hind gut. It extends between amnion and chorion. It is rich in blood. It plays a vital role in excretion and respiration. It is small and non functional in human beings. The yolk sac is formed in reptiles, birds and egg laying mammals. The yolk is surrounded by it. It helps to absorb the nutrient materials. It is non functional in human beings.
The reptiles are quite successful on land. This is mainly due to the process of internal fertilization and the scales on their body which make them not to loss water. The amnion provides a watery environment to the embryo when it develops. The shell is present which prevent desiccation.
The body of tortoise and turtles is covered by a shell. It consists of plastron and carapace. These structures are present on the ventral and dorsal surfaces respectively. They are mostly vegetarian. They are also flesh eaters. It includes the giant tortoise which is the longest living animal.
