Class Reptilia comprises a diverse group of cold-blooded vertebrates that includes snakes, lizards, turtles, crocodiles, and tuataras. Reptiles are characterized by their scaly skin, which helps prevent water loss, and their ability to lay shelled eggs on land, though some species give live birth.
General Characters of Class Reptilia:
1) Habitat: They are inhabitants of terrestrial and aquatic (both marine & fresh water) environments.
2) Skin/Body: The skin is rough and dry usually covered with epidermal scales and sentes.
3) Limbs: Two pairs of pentadactyle limbs are present (Exception: Snakes) with clawed digits.
4) Tail: A post-anal tail is present.
5. Heart: Heart is consists of two auricles and a partially divided ventricle. (Exception: 4 chamber heart in Crocodiles)
6) Kidney: The Kidney is metanephric type.
7) Skull: Single occipital condyle present in Skull i.e. Monocondylic.
8) Cranial Nerves: 12 pairs of Cranial nerves present.
9) Nose/Ear: Single external nasal opening is present on the stout. Ear drums are slightly depressed.
10. Cloaca: Cloacal opening is either transverse/longitudinal.
11) Special organ: Vomero-nasal organ (Organ of Jacobson) is well developed.
12) Respiration: Respiration always takes place through lungs.
13) Body temperature: They are poikilothermic (Cold blooded) animals.
14) Fertilisation Fertilisation is internal.
15) Eggs: Cleidoic eggs are large (Macrolecithal eggs).
16. Duct: Mullerian duct persists as oviduct in female and Wolffian duct is retained as vas deference in male.
17. Mandible: Mandibles consists usually six pieces of bones.
18. Embryo: Embryos are provided with extra-embryonic membranes like amnion, chorion and allantois.
Example: Testudo sp. (Tortoise); Hemidactylus sp. (House lizard); Naja naja (Cobra); Crocodilus sp. (Crocodile) etc.
Classification of Class Reptilia:
1) Sub Class: Anapsida
- Order: Chelonia
2) Subclass: Lepidosauria
- a) Order-Rhynchocephalia
- b) Order- Squamata
3) Sub Class: Archosauria
- Order: Crocodilia
1) Sub Class Anapsida:
- i) The skull is devoid of fossae.
- ii) The roof of the skull is solid and bony.
Order: Chelonia (Chelone = tortoise):
- Body is dorsoventrally flattened and more or less elliptical.
- Body is dorsally covered by a shield like Carapace and ventrally by a plate Plastron.
- Neck, limbs and tails are retractile.
- Weak limbs are pentadactyl and in some marine forms modified into paddles.
- In adults, teeth are absent and the jaws are covered by sharp horny plates.
- The cloacal opening is longitudinal.
- These are oviparous animals.
- All Chelonians are hibernate in temperate regions.
- Pectoral girdle consists of a scapula, a long pro-coracoid and a coracoid.
Example: Testudo sp. ; Thionyx sp.; Lepidochelys olivacea etc.
2) Subclass Lepidosauria (Lepis- scale, Squaros= Lizard)
- (i) The skull of these organisms has two temporal fossa, i.e diapsid skull.
- (ii) Lizard like reptiles with scaled skin.
a) Order- Rhynchocephalia (Rhynchos = a snout; Kephale = head)
- The skin is dorsoventrally dull olive green and ventrally whitish in colour.
- Tail is bilaterally compressed have.
- The eyes are large with vertical pupil.
- Almost all vertebrae possess Chevron bone.
- Teeth are of acrodont type. Small triangular teeth present.
- The fertilised eggs teeth take over a year to hatch.
Example: Sphendon punctatus and S. guntheri.
b) Order- Squamata (Squamatas = scaly)
- The skull of these animals bears superior temporal fossa.
- Lower jaw is composed of several pieces of bones.
- Teeth are either acrodont, or pleurodont.
- Organ of Jacobson is well developed.
- Cloacal aperture is a transverse slit.
- Vertebrae are of procoelous type and possess chevron bone.
- The ribs are single headed.
- They are distributed all over the world i.e Cosmopolitan.
Example: Hemidactylus sp. (House lizard); Gekko sp. Draco sp. (Flying Lizard), Chamaeleon sp. (chameleon). Phython sp; Hydrophis sp; Naja naja (Cobra)
3. Sub Class Archosauria:
- i) The skull is diapsid type.
- ii) Some forms are toothless and in others only Palatal teeth are lost.
- iii) The lower jane is with vacuities between dentary and angular.
- iv) In some advanced forms bipedality was present.
Order Crocodilia (Crocodilus = Crocodile) or Loricata:
- These are fresh water reptiles and carnivorous habit. They swim by powerful laterally compressed tail.
- Creep on land with the help of weak limbs.
- Pentadactyl limbs, forelimb possess webbed digits.
- The skin bears epidermal scales. The scales are supported by dermal bones or scutes.
- The cloacal aperature is longitudinal.
- The heart is four chambered.
- The eyes are provided with pecten.
- The nostrils are situated at the tip of snout.
- Thecodont type of teeth present.
- Males have single and median erectile copulatory organ. A clitoris is present in female.
Example: Crocodylus palustris (Indian); C. porosus ; Alligator mississippiensis (American); A. sinensis (China); Gravialis gangeticus (Gharials of India, Ganga river).