Classify Reptiles upto orders giving salient features and examples

Reptiles represent the first class of vertebrates fully adapted for terrestrial life can be live indefinitely out of water. They have no diagrostic characteristics of their own that immediately separate them from other classes of vertebrates. The characters of reptiles are in fact a combination of characters that are found in fish and amphibians on one hand and in birds and mammals on the other. The class name refers to the mode of locomotion (L., repere or reptum, to creep or crawl).

The class reptilian has been classified into five major sub-classes on the basis of presence or absence of certain openings in the temporal region of skull. There are more than 7,000 living and several extinct species which are grouped into 16 orders under the five sub-classes. Out of the 16 orders 4 are living and others are extinct.

Sub-class-I – ANAPSIDA

(i) Roof of skull is complete and no temporal openings.

This sub class includes one living order.

Order – 1 – Chelonia or Testudinata

(i) Body is short, broad and oval.

(ii) Limbs clawed and webbed and paddle like.

(iii) Body encased in a firm shell of dorsal carapace and ventral plastron, made of dermal bony plates.

(iv) Thoracic vertebrae and ribs usually fused to carapace.

(v) No sternum is found.

(vi) Teeth absent Jaws with horny sheath.

(vii) Cloacal with a longitudinal slit.

(viii) Heart incompletely 4 – chambered.

(ix) Copulatory organ simple and single.

(x) Quardrate is immovable. Nasal opening single and media.

(xi) Oviparous.

(xii) There are about 400 species.

Example – Chelene, Testudo, Trionyx.

Sub-class – II – EURYAPSIDA (Extinct)

(i) Skull with a single dorso-lateral temporal opening on either side.

(ii) These openings are bounded below by postorbital and squamosal bones.

(iii) They lived during Triassic period.

Sub-class-III PARAPSIDA (Extinct)

(i) Skull with a single dorso-lateral temporal opening on either side.

(ii) These openings are bounded below by the supratemporal and postfrontal bones.

(iii) They lived during Mesozoic to cretaceous period.

Ex: – Ichthyosaurus, mixosaurus etc.

Sub-class – IV – SYNAPSIDA (Extinct)

(i) Skull with a single lateral temporal opening on either side.

(ii) These openings are bounded above by the postorbital and squamosal bones.

(iii) They lived during carboniferous to perform period.

Sub-class – V – DIAPSIDA

(i) Skull with two temporal openings on either side separated by the bar of postorbital and squamosal bones.

This sub- class includes 3 orders.

Order – 2 Rhynchocephalia

(i) Body small, elongated, lizard –like

(ii) Limbs pentadactyle, clawed and burrowing.

(iii) Skin covered by granular scales and a mid-dorsal row of spines.

(iv) Vertebrae amphicoelous or biconcave.

(v) Numerous abdominal ribs present.

(vi) Teeth acrodont.

(vii) Cloacal aperture transverse/

(viii) No copulatory organs in male.

Example – Represented by a single living species, Sphenodon punctatum or tuatara

Order – 3 Squamata

(i) Body small to medium, elongated and advanced.

(ii) Limbs, clawed, absent in snakes and few lizards.

(iii) Body covered by homy epidermal scales, shields and spines.

(iv) Vertebrae procoelous.

(v) Ribs single headed.

(vi) Teeth acrodent or pleurodent.

(vii) Cloacal aperture is transverse

(viii) Male with eversible double copulatory organs (hemipenes)

This order includes two sub-orders.

Sub order – 1 Lacertilia

Sub order – 2 Ophidia

Suborder – 1 – Laoertilia

(i) Commonly known as lizards.

(ii) Limbs and griddles usually well-developed.

(iii) Eyelids movable. Nictitating membranes present.

(iv) Ear openings and tympanum present.

(v) Maxillae, palatines ad pterygoids fixed.

(vi) Mouth non-expansible.

(vii) Sternum, episternum and urinary bladder usually present.

(viii) Tongue rarely notched or extensile.

Example – hemidactylus, Calotes, Uromastix Varanus, Chamaeleon, Draco.

Sub- order – 2 Ophidia

(i) Commonly known as snakes.

(ii) Limbs and griddles absent, vestigial hindlimbs and pelvic girdle in boa, python etc.

(iii) Eye lids fixed. Nictiating membranes absent.

(iv) Auditory openings and tympanum lost.

(v) Manilae, palatines and pterygoids movable helping in bifing mechanism.

(vi) Mouth can be widely separated.

(vii) Sternum, episternum and urinary bladder usually absent.

(viii) Tongue slender, bifid and extensible.

Ex – Python, Boa, Naja, Bungarus, Vipera etc.

Order – 4 – Crocodile

(i) Body large-sized, carnivorous and aquatic reptiles.

(ii) Limbs short but powerful, clawed and webbed.

(iii) Tail long, strong and laterally compressed.

(iv) Body surface covered by horny epidermal scales, bony plates and scutes.

(v) Teeth thecodont, numerous.

(vi) Abdominal ribs present.

(vii) Cloacal aperture is a longitudinal slit.

(viii) Heart completely 4 chambered.

(ix) Male with a median, erectile, grooved penis.

Ex – Crocodylus, Alligators etc.