Classification of Animal Chordates of Class 11
Study of reptiles is called Herpetology.
Reptiles represent the first class of vertebrates fully adapted for the life in dry places on land.
Predominantly terrestrial, creeping or burrowing, mostly carnivorous, air-breathing, cold-blooded, oviparous and tetrapodal vertebrates.
Limbs 2 pairs, pentadactyl. Digits provided with horny claws. Limbs absent in all snakes.
Exoskeleton of horny epidermal scales, shields, plates and scutes.
Skin dry, cornified and devoid of glands.
Mouth terminal. Jaws bear simple conical teeth. Teeth are absent in chelonians.
Alimentary canal terminates into a cloacal aperture.
Endoskeleton bony. Skull with one occipital condyle.
Respiration occurs by lungs. Only ribs help expand and contract the trunk, making lung respiration more efficient than in amphibians.
The heart is incompletely four-chambered. Sinus venosus is present, but truncus arteriosus is absent. Crocodiles have a completely four-chambered heart like the birds and
mammals. Renal portal system is reduced. Red blood corpuscles are oval, biconvex and nucleated.
There are 12 pairs of cranial nerves.
Waste material is removed chiefly as uric acid in land forms and as urea in aquatic forms. Urinary bladder may be present.
Lateral line system absent. Jacobson’s organs (sense of smell) present in the roof of mouth.
Sexes separate. Male usually with a muscular copulatory organ.
Fertilization internal. Mostly oviparous.
Large yolky eggs covered with leathery shell, embryonic membranes (amnion, chorion, yolk sac and allantois) appear during development.
Direct development without any larval stage.
Parental care usually absent.
Living Reptiles are divided as follows :
The class Reptilia is first divided into 5 major groups or subclasses on the basis of presence or absence of temporal openings through the posterolateral or temporal region of the skull.