GENERAL CHARACTERS

The term Reptilia originated from Latin word Repto / Reptor –Creep/crawl

Study of reptiles ( herpeton) -Herpetology

Reptiles are predominently terrestrial( land dwelling) , creeping, burrowing , mostly carnivorous, poikilothermic (cold blooded) , mostly oviparous (egg laying) ,tetrapod (four legged) verebrates .

Some Reptiles are aquatic example : Chelone

Some are arboreal (dwell on trees ) example :Chameleon

Body form of Reptiles varies , it may be short, long , broad, narrow, broad,cylindrical or depressed.

Body is divided into – head, neck, trunk and tail.Appendages – two pairs of limbs ending in five

digits each (pentadactyl) ,ending in claws.Limbs maybe modified into paddles for

swimming Example : Chelone

In snakes limbs are absent.

Skin is dry, rough and non-glandular ,covered by an exo-skeleton of horny epidermal scales ,bony plates or bony scutes  made of keratin.

 Most lizards and snakes have overlapping scales arranged diagonally and also into spikes, emphasizing protection from other animals.  By emphasizing skin color, scales help play a role in defense, courtship, and territorial acts.  

Since most reptiles are cold-blooded or ecto -thermic, they are unable to produce their own body heat in which they rely on the sun and the scales help to keep body heat in.  

Scales are of many types – granular(appear bumpy) ,keeled (have a centre ridge).Scales vary in size –stouter larger scales cover parts that are often exposed to stress( feet,tail and head).Scales are small around the joints for flexibility.In crocodiles the scales are modified into plate-like scutes . Turtles and tortoises have shell made of bony plates to protect their soft bodies

 Most lizards and snakes have overlapping scales arranged diagonally and also into spikes for protection from other animals.

 Colouration of scales help in defense, courtship, and territorial acts.

 Since most reptiles are cold-blooded or ecto thermic, they are unable to produce their own body heat so they rely on the sun rays and the scales help to keep body heat in.  

Reptiles are poikilothermic or cold blooded forms,the body temperature varies according to that of the environment.

Endo skeleton is completely ossified.Skull is monocondylar (single occipital condyle)

Skull may have temporal fossa

Brain in Reptiles well developed. 12 pairs of cranial nerves .

Sense organs in ReptiliaSenses of smell and vision well developed

.Snakes have additional Jacobson’s organ for smelling . Sense of hearing is poor ,they can only perceive vibrations of the earth.

Digestive system in Retiles is complete. Alimentary canal leads into cloacal chamber .

Respiration in Reptiles takes place by lungs (pulmonary) throughout life.

Turtles also have cloacal respiration .

Heart in Reptilians is incompletely four chambered, having two auricles and partly divided ventricle.

They have systemic and pulmonary circulation.

Crocodiles have four chambered heart .

RBCs are nucleated, oval shaped and biconvex

Excretion in Reptiles is performed mainly by two small metanephric kidneys. Uric acid  is the main nitrogenous waste product (uricotelic forms),turtles excrete mainly  urea .

Reptile kidneys are unable to produce liquid urine more concentrated than their body fluid because they lack loop of Henle in the nephrons.

Reptiles use the colon to aid in the reabsorption of water. Some are also able to take up water stored in the bladder . Excess salts are also excreted by nasal and lingual salt glands in some reptiles like chelones .

Reptiles generally reproduce sexually . Most reptiles have copulatory organs, which are usually retracted or inverted and stored inside the body.

In turtles and crocodilians, the male has a single median penis, while squamates, including snakes and lizards, possess a pair of hemipenes.

Most reptiles lay amniotic eggs covered with leathery or calcareous shells. An amnion , chorion, and allantois are present during embryonic life. The shell protects and keeps it from drying out, but it is flexible to allow gas exchange. The chorion aids in gas exchange .The albumin serves as a reservoir for water and protein. The allantois collects the metabolic waste produced by the embryo. The amniotic sac with amniotic fluid which protects and cushions the embryo. The amnion aids in osmoregulation .The yolk sac surrounding the yolk contains protein and fat rich nutrients that are absorbed by the emryo. The air space provides the embryo with oxygen while it is hatching. This ensures that the embryo will not suffocate while it is hatching.

Mostly oviparous forms –lay cleidoic (yolk laden) eggs. There are no larval stages in development.

In some forms like Viper ovoviviparity is seen, fertilized eggs develop and hatch inside the mother, who then gives birth to live young ones which resembles the adult .

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