Subclass I Anapsida

Classification of Animal Chordates of Class 11

Primitive reptiles with a solid skull roof. No temporal openings.

Order 1 : Chelonia or Tesatudinat

(Gr., chelone, turtle; L., testudo, turtle)

Body short, broad and oval.

Limbs clawed and/or webbed, paddle-like.

Body encased in a firm shell of dorsal carapace and ventral plastron, made of dermal bony plates. Thoracic vertebrae and ribs usually fused to form carapace.

Skull anapsid, with a single nasal opening and without a parietal foramen.

No sternum is found.

Teeth absent. Jaws with horny sheaths.

Cloacal aperture a longitudinal slit.

Heart incompletely 4-chambered with a partly divided ventricle.

Copulatory organ single and simple.

Life span very long.

About 400 species of marine turtles, freshwater terrapins and terrestrial tortoises.

Examples : Chelone, Chrysemys, Trionyx, Dermochelys, Testudo

Table : Difference between Tortoise & Turtle

Subclass II Euryapsida (extinct) : Skull with a single dorso-lateral temporal opening on either side bounded below by postorbital and squamosal bones.

Subclass III Parapsida (extinct) : Skull with a single dorso-lateral temporal opening on either side bounded below by the supratemporal and postfrontal bones.

Subclass IV Synapsida (extinct) : Skull with a single lateral temporal opening on either side bounded above by the postorbital and squamosal bones.

Subclass V Diapsida : Skull with two temporal openings on either side separated by the bar of postorbital and squamosal bones.

Order 2 : Rhynchocephalia

(L., rhynchos, snout +Gr., kephale, head)

Body small, elongated, lizard-like.

Limbs pentadactyle, clawed and burrowing.

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

Skull diapsid. Nasal openings separate. Parietal foramen with vestigeal pineal eye present.

Vertebrae amphicoelous or biconcave. Numerous abdominal ribs (gastralia) present.

Teeth acrodont. Cloacal aperture transverse.

Heart incompletely 4-chambered.

No copulatory organ in male.

Example : It is found only in New Zealand. it is at verge of extinction. It has well developed third eye or Parapineal eye or parietal eye. It is also called living fossil. Eg. “Hatteria” or “tuatara” or Sphenodon punctatum of New Zealand.

Order 3 : Squamata

(L., squama, scale or squamatus, scaly)

Advanced, small to medium, elongated.

Limbs clawed, absent in snakes and few lizards.

Exoskeleton of horny epidermal scales, shields and spines.

Skull diapsid.

Vertebrae procoelous. Ribs single - headed.

Teeth acrodont or pleurodont.

Heart incompletely 4-chambered.

Cloacal aperture is transverse.

Male with eversible double copulatory organs (hemipenes).

About 6,800 species of lizards and snakes. These are divided into 2 distinct sub-orders:

Sub-order 1 : Lacertilia (Sauria) e.g., Lizards. (Study of lizards is saurology)

Sub-order 2 : Ophidia e.g. Snakes. (Study of snakes is ophiology or serpentology)

Table : Difference between Lizard and Snake

Snakes

A typical snake is elongated and devoid of limbs. The body is covered with scales.

The tympanic membrane and tympanic cavity are absent. The eyelids are absent but, if present are immovable. The nictitating membrane is absent.

The tongue is long, bifid and protrusible.

The sternum is absent. Urinary bladder is absent. There are no vocal cords, therefore, snakes can only hiss through the nostrils.

The locomotion is brought about by the lateral body wall muscles through the movement of the ribs.

The sound waves are picked up by the general body surface.

Both upper and lower jaws bear teeth. In poisonous snakes, a pair of teeth on the upper jaw, become large for biting, which are called fangs. There is present a pair of poison glands, each opening at the base of fang of its side by means of a poison duct. Generally, poisonous snakes leave two fang marks, rarely one if it is a side-bite. Non-poisonous snakes usually produce a row of U-shaped teeth marks.

Poisonous snakes (Venomous snakes) : Cobra, Krait, Viper, Pit viper, Russel viper, Sea snake, Coral snake and Rattle snake.

Non Poisonous Snakes : Python, Typhlops (Blind snake), Rat snakes, Tree snakes, double headed snake. 90% of snakes are non-poisonous.

Neurotoxic Venom : It acts on nervous system e.g., venom of Cobra, Krait and Sea snakes.

Haemolytic Venom : It breaks down red blood corpuscles e.g. venom of Viper.

Subclass I Anapsida

Fig. Diagram for identification of poisonous and non-poisonous snakes

Table : Identification of poisonous and non-poisonous snake

Order 4 : Crocodilia

(G., krokodeilos, Crocodile)

Large-sized, carnivorous and aquatic reptiles.

Tail long, strong and laterally compressed.

Limbs short but powerful, clawed and webbed.

Skin thick with scales, bony plates and scutes.

Skull diapsid.

Abdominal ribs present.

Teeth numerous, thecodont, lodged in sockets.

Heart completely 4-chambered.

Cloacal aperture is a longitudinal slit.

Male with a median, erectile, grooved penis.

Example : Crocodylus, Gavialis, Alligator

Subclass I Anapsida

Table : Differences between Crocodile, Alligator and Gavialis

POINTS TO REMEMBER

Mesozoic era is known as ‘golden age of reptiles.’

Seymouria is considered as connecting link between amphibians and reptiles.

Loreal pit of pit viper is thermoreceptor organ.

Reptiles without urinary bladder-snakes, crocodiles, alligators.

Many sea snakes are viviparous. Pit vipers are mostly viviparous.

The king cobra of India is the only snake in the world that builds a nest.

The oldest living animal in any Indian Zoo is the Aldabra giant tortoise. (Calcutta zoo)

Rattle snakes’s tail emits a frightening sound which scares away the enemy.

Benadryl is used as an antidote to counteract the effect of haemotoxins.

Largest Snake - Python; Smallest Snake-Thread snake.

Largest Lizard-Komodo dragon; Smallest Lizard-Two species of dwarf gecko.

Long dinosaur - Diplodocus; Small dinosaur - Compsognathus.

Largest Living Reptiles (i) Python, (ii) Crocodile (iii) Komodo dragon.

Heloderma is the only poisonous lizard. It is found in Mexico & Arizona.

Hemidactylus or wall lizard is a swift runner on smooth vertical surface due to the presence of vacuum pads.

Draco is flying lizard but it actually does not fly, it can glide

Ophiosaurus known as ‘glass snake’, ‘blind worm’, or ‘slow worm’. It is a limbless lizard.

Anguis is also blind worm and limbless.

Most venomous Indian snake-king cobra.

Most Poisonous snake of world-Peninsular Tiger Snake.

Poisonous sea snake-Hydrophis, Enhydrina

Heaviest dinosaurs-Brontosaurus.

Largest flesh eater dinosaur - Tyrannosaurus.

Horned dinosaur - Stegosaurus.

Varanus - Monitor lizard (largest living lizard), also called “Goh” or common Indian monitor.

Reptiles arose in the lower carboniferous time, from Labyrinthodon amphibia.

Phrynosoma is found in deserts; called “Horntoed”, skin hygroscopic; takes water in the form of dew; exudes red blood-like stream from eyes, whenever, terrified.

Iguana is 5-6 feet long; body and tail laterally compressed; arboreal in habit; herbivorous found in tropical America.

Sphenodon is the only living genus of Rhynchocephalia. It is commonly called Tuatara. Found only in New Zealand.

Largest living carnivorous reptile is Crocodilus.

Theromorpha is a group of reptiles which are considered as ancestors of mammals.

Hedonic glands present in males, secrete sticky substance which hardens like spine and help to hold the mates firmly.

In Uromastix, cloaca possesses a pair of copulatory organs called hemipenis.

Russel’s viper is the largest Indian viper.

Hofkin’s Institute of Bombay cemtral Research Institute Kasauli are the main centres where anti-venom is produced.

Limbs of Chameleon show syndactly (fusion of digits) as an adaptation to arboreal life to form opposable finger to hold the twigs.

Tortoise has the longest life-span in the animal world.

Hemidactylus (House Gecko) loses its tail when it is attacked by enemy and the phenomenon is called autotomy.

Patagium-A thin fold of integument on the sides of body of lizard supported by bony ribs, act as parachutes and help in gliding.

Sloughing in snakes-Exoskeleton of horny scales periodically moulted in one piece. It is called Ecdysin.

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