Class Reptilia includes the turtles and tortoises (order Chelonia), lizards and snakes (order Squamata), crocodiles and alligators (order Crocodilia) and tuatara (order Rhynchocephalia). These represent only 4 of the 16 orders that lived and flourished in Mesozoic era. Class Reptiles are first vertebrates adapted for life on dry land. The class name refers to the mode of travel (Latin reptum=to creep). Class Reptiles animals show advance over the amphibians in having (i) dry scaly body covenng, adapted to life away from water, (ii) limbs suited for rapid locomotion, (iii) further separation of oxygenated and non-oxygenated blood in the heart, (iv) complete ossification of skeleton, and (v) eggs sutted for development on land with membranes.
Most reptiles live in tropical and subtropical regions, their number declining towards poles. Turtles and snakes are abundant in humid regions. Class Reptiles have radiated towards all kinds of habitat, i.e., land, water and air. In winter they lead dormant life, hibernate in crevices. Snakes are injurious to mankind and still man fears them very much. Many kinds of snakes and lizards benefit man by providing food, by destroying harmful rodents and insects. Skin of snakes and crocodiles is of great economic importance.
DIAGNOSTIC CHARACTERS OF CLASS REPTILIA
- Body covered with dry skin.
- Horny epidennal scales, shields, plates and scutes fonn exoskeleton.
- Hind and forelimbs present. Digits with horny claws.
- Single occipital condyle.
- Bony endoskeleton.
- Fertilization internal.
CLASSIFICATION OF CLASS REPTILIA
SUB-CLASS A :- ANAPSIDA
- Skull roof solid.
- No temporal opening behind eye.
Order 1. Cotylosauria
- Primitive reptiles.
- Resemble Labyrinthodont amphibians.
Example :- Seymouria
Order 2. Chelonia
- Body broad, covered with a finn shell of rounded dorsal carapace and flat-ventral plastren.
- No teeth. Jaws with horny sheath.
Sub-order 1. Atheca – Extinct
Sub-order 2. Thecaphora
- Neck bends in vertical scurve if retractile.
- Pelvis not fused with plastron.
Family 1. Testudinidae
- Shell usually complete with scutes.
- Limbs with claws, not paddle-like.
Example :- Chrysemys, Terrapene, Testudo, Kachuga
Family 2. Chelonidae
- Limbs flipper-like, shell shield smooth.
- Horny scutes large.
Example :- Chelonia, Coretta, Chelone
Family 3. Trionychoidae
- Soft, shelled turtles.
- Shell reduced covered by skin.
Example :- Trionyx
SUB-CLASS B :- EURYPSIDA
- Skull with single dorsolateral temporal opening bounded by post -orbital and squamosal.
Example :- Plesiosaurus.
SUB-CLASS C :- PARAPSIDA
- Dorsolateral temporal opening in skull bounded by supra-temporal and post Frontal.
Example :- Ichthyosaurus.
SUB-CLASS D :- SYNAPSIDA
- Skull roof with lower opening behind eye bounded above by post-orbital and squamosal.
- Extinct mammal-like reptiles.
Example :- Dimetrodon, Varanosaurus.
SUB-CLASS E :- DIAPSIDA
- Skull roof with 2 openings behind eye separated by a bar formed by post-orbital and squamosal.
- No antero-orbital opening or depression.
Order 1. Rhynchocephalia
- Living reptiles, lizard-like.
- Scales granular, a mid-dorsal row of long spines.
Example :- Sphenodon
Order 2. Squamata
- Lizards and snakes.
- Skin with horny epidermal scales or shields.
Sub-order 1. Sauria or Lacertilia
- Lizards. Body slender. Limbs typically 4.
- Eyelids movable.
Family 1. Geckonidae
Family 2. Iguanidae
Family 3. Agamidae
Family 4. Scincidae
- Limbs and toes often reduced sometimes absent.
- Scales commonly smooth.
Example :- Mabouia
Family 5. Chamaeleonidae
- Head angular produced into snout.
- Tail prehensile. Changes colour.
Example :- Chameleon
Family 6. Varanidae
- Large trunk. Limbs stout. Neck and tail long. Monitors.
- Teeth pleurodont. Tongue long bifid and protrusible.
Example :- Varanus
Family 7. Helodermidae
- Poisonous lizards. Rounded limbs. Trunk and tail stout
- Tongue fleshy and protrusible.
- Venom potent, fatal to small animals, rarely to man.
Example :- Heloderma
Family 8. Anguidae
- Alligator lizards. Body slender with deep fold in skin on each side.
- Limbs small or none. Tail long, fragile and regenerates.
Example :- Anguis, Ophiosaurus
Sub-order 2. Ophidia or Serpentes
- Snakes, limbs, feet, ear openings, sternum and urinary bladder absent.
- Mandibles joined anteriorly by ligament.
- Poisonous and non-poisonous snakes.
Family 1. Typhlopidae
- Eyes vestigial under opaque scales, teeth on maxillary bones only.
- Scales thin, overlapping.
Example :- Blind snakes (Typhlops)
Family 2. Leptotyphlopidae
- Teeth only on lower jaw.
- Vestiges of femur and all pelvic bones present.
Example :- Leptotyphlops
Family 3. Boidae
Family 4. Anilidae
- Head small, cranium firm.
- Tail short, scales smooth.
Example :- Anilius, Cylindrophus
Family 5. Uropeltidae
- Head small and pointed. Tail short, shield tailed snakes.
- No vestiges of hind limbs and pelvic girdle.
Example :- Uropeltis
Family 6. Colubridae
- Facial bones movable, squamosal loosely attached to articular.
- Both jaws with teeth but no elaborate fangs.
Example :- Ptyasmucosus, Matrix, Dendrophis
Family 7. Dasypeltidae
- Ventral spine on anterior vertebrae used to crack shells of birds eggs.
- Teeth long and slender.
Example :- Elachistodon, Dipsas
Family 8. Hydrophiidae
- Tail compressed, used for swimming, venomous and dangerous to man.
- A pair of short, rigid, erect venom-conducting teeth or fangs.
Example :- Sea snakes (Hydrophis), Pelamis
Family 9. Elapidae
Family 10. Viperidae
- Paired erectile fangs in front of upper jaw, one on each maxillary bone and folded backward when not in use. Venomous.
- No pit between nostril and eye.
Example :- Vipera russelii (pitless viper)
Family 11. Crotalidae
Order 4. Pseudosauria :- Extinct. Ex. Saltopseudois.
Order 5. Saurischia
- Ischium and pubis diverge.
- Bipedal or huge 4-footed.
Example :- (Extinct) Dinosaurs, Tyrannosaurus, Brontosaurus, Diplodiscus
Order 6. Ornithischia
- Pelvis bird-like.
- Ischium and pubis together.
- Extinct. Example :- Dinosaurs, Iguanodon, Triceratops, Stegosaurus
Order 7. Pterosauria
- Flying reptiles.
- Forelimbs with wing membranes. Tail long.
Example :- (Extinct) Pteranodon, Rhamphorhynchus