Reptiles represent the primary category of vertebrates absolutely tailored for all times in dry places ashore. They need no distinguished diagnostic characteristics of their own that straight off separate them for different forms of vertebrates. The characters of reptiles area unit a mix of characters that are found in fish and amphibians on the one hand and in birds and mammals on the other. The category name refers to the mode of locomotion (L., repere or reptum, to creep or crawl), and also the study of reptiles is termed herpetology (Gr., herpeton, reptiles).
Mainly terrestrial, crawling or burrowing, largely carnivorous, air-breathing, cold-blooded, oviparous and tetrapodal vertebrates.
The body is bilaterally symmetrical and partible into four regions- head, neck, trunk and tail.
Limbs a pair of pairs, pentadactyle. Digits supplied with horny claws. However, limbs absent in a very few lizards and all snakes. Sometime vestigial hindlimbs can be seen in some snakes like Python.
The exoskeleton of horny stratum scales, shields, plates and scutes. Snakes shed their scales as skin casts.
Skin dry, cornified and void of glands.
Mouth terminal. Jaws bear easy cone-shaped teeth. In turtles teeth replaced by horny breaks.
Alimentary canal terminates into a cloacal aperture.
Endoskeleton bony. Bone with one bone process (monocondylar). A characteristic T–shaped inter clavicle present.
The heart sometimes 3–chambered, 4–chambered in crocodiles. Sinus venosus reduced. a pair of general arches gift. Red blood corpuscles oval and cell organ. Cold-blooded.
Respiration by lungs throughout life.
Kidney metanephric. Excretion uricotelic.
Brain with higher development of neural structure than in Amphibia. Cranial nerves twelve pairs.
Lateral line system absent. Jacobson's organs gift within the roof of the mouth.
Sexes separate. Male sometimes with a muscular copulatory organ.
Fertilization internal. Largely broody. Giant yolky meroblastic eggs lined with coriaceous shells, continually set ashore. Embryonic membranes (amnion, chorion, food sac and allantois) seem throughout development. No metamorphosis. Young resemble adults.