Survey of the Reptiles – Structure and characteristics of Reptiles


Reptiles have Following characteristics:

1. Their skull has one surface (condyle) for articulation with the first neck vertebra.

2. Respiration takes place by lungs.

3. They have metanephric (kidney Formed From the lower part of the middle part of  ancestral kidney) kidneys.

4. They have internal fertilization and amniotic eggs.

4.Reptiles have dry skin. It has keratinized epidermal scales. Keratin is a resistant protein. It is found in epidermally derived structures of amniotes. It is chemically bonded to phospholipids. Therefore, it prevents loss of water through body surfaces.

5. They are found on all continents except Antarctica. However, they are most abundant on tropical and subtropical environments. There are 17 orders of reptiles.


1. Teeth  are absent in adults. They are replaced bv a horny beak. The have keratinized beak.

2. Thev have short broad body.

3. Their shell consists or a dorsal carapace and ventral plastron.

4. Turtles have 225 species. They have a bony shell.

5. Their limbs articulate internally with the ribs.

Example: Turtles

Shell in turtles

Carapace: The dorsal portion of  the shell is the carapace. Carapace is formed bv the fusion of vertebrae, ribs and bones in the dermis of skin. Keratin covers the bone of the carapace.

Plastron: The ventral portion or the shell is plastron. It is formed from bones of  pectoral girdle and dermal bone. Keratin also covers it. The shell of some turtle has flexible areas or hinges. These hinges attach the anterior and posterior edges of the plastron. The hinges close the openings 0f the shell during withdrawal of body into the shell.

Turtles have eight cervical vertebrae.These  vertebrae can bearticulated to form an S-shaped structure. It draws the head into the shell.


Reproduction and life span

Turtles have long life spans. Most turtles reach at sexual maturity after seven or eight years. They can live 14 or more years. The age of  large tortoises of the Galapagos Islands may be above 100 years. All turtles are oviparous. Females use their hind limhs to dig nests in the soil. There they lay eggs. Their clutches contain 5 to 100 eggs.

They cover the eggs with and soil. Development takes from four weeks to one year. The parent does not attend to the eggs during this time. The young are independent of the parent at hatching.

Turtles in danger

Turtules have slow rates of growth. Therefore, they have long juvenile periods. Therefore, they have high mortality rates. Thus turtles are becoming extinct. Turtle conservation programs have been started in recent years. Dogs and other animals are hunting young turtles. It has severely threatened some species of turtles. These species are sea turtles. They make nest on certain beaches year after year.  Conservation programme of sea turtles is difficult. Theyhave ranges of thousands of square kilometers of ocean. The protectiveareas include waters of different countries.

ORDER RHYNCHOCEPHALIA (rhynchos. snout + kephole, head)

Rhynchocephalia has only one surviving species called tuatara (Sphenodon pundalus). It is lizard like reptile. It has remained unchanged since it evolved from its extinct relatives. Its relatives were present at the beginning of the Mesozoic era nearly 200 million years ago.

Distinctive features: Tooth attachment and structure distinguish the tuatara from other reptiles. They have two rows of teeth on the upper jaw and a single row of teeth in the lower jaw. They bite the birds with these teeth. This biting can decapitate a small bird. It was widely distributed in New Zealand. The population of tuatara is affected by human influences and domestic animals. It is now present only on far off offshore islands. It is protected by New Zealand law. It is oviparous and it shares underground burrows with ground nesting seabirds. Tuataras come out of their burrows at dusk and dawn. They feed on insects or sometimes on vertebrates.


ORDER SQUAMATA (Snakes and Lizards) (squama, scale + ata, hear)

1. Thev have specific characteristics of the skull and Jaws. Temporal arch are reduced or absent. They quadrate bone is moveable or fixed.

2. They are the most successful and diverse group or living reptiles.

Examples: Snakes, lizards, worm lizards

The order Squamata is divided into three suborders. Ancestral member of these suborders originated in the lepidosaur lineage about 150 million years ago.

a) Suborder Sauria: The Lizards

1. Suborder Sauria have about 3, 300 species of lizards.

2. The lizards have two pairs of legs.

3. Their upper and lower jaws arc united anteriorly.

4. Few lizards are legless. But they retain remanants of a pectoral girdle and


5. Lizards vary in length. Their length may be from a few centimeters to 3m.

6. Many lizards live on surface substrates. They move down under rocks or logs when necessary. Others are burrowers or tree dwellers.

7. Most lizards are oviparous. Some are oviviparous or viviparous. They deposit eggs under rocks or debris or in burrows.


Geckos are commonly found on the walls of houses  in semitropical areas. Their body is short and stout. They are nocturnal. They produce the sound of clicking. They have large eyes,  their pupil contract and narrow during the day. It widens at night. This is an adaptation for night vision. They has adhesive disks on their digits. These disks help in clinging to trees and walls.



Iguanas have heavy bodies. They have short necks and distinct heads. This group includes the marine iguanas of the Galapagos Islands and the flying dragons (Draco) of southeast Asia. Darco has lateral folds of skin. It is supported by ribs. The ribs of Draco can expand to form gliding surface. It can glide 30 m or more.


It is another group of iguanas. It is found in Africa and India. Chameleons are adapted for aboreal lifestyles. They use a long sticky tongue to capture insects.



Anolis, the pet-store chameleon”is also an iguanid. But it is not  a true chameleon. Chamelons and Anolis are well known for their ability to change color. They change their body colour in response to illumination, temperature or their behavioral state.


Venomous lizards

They are the gila monster (Heloderma suspectum) and the Mexican beaded lizard southwestern North America(Heloderma horridum). These heavy bodied lizards live in southwestern America. The surface of their teeth have groove. Venom is releascd into these grooves. The lizard chews the prey and introduces venom into it. Lizard bites are not fatal to humans.

(b) Suborder Serpentes (serpere,

There are about 2, 300 species in the suborder Serpentes. Majority of snakes are not dangerous to humans. But three hundred species are venomous. 30, 000 to 40, 000 people the from snake bites each year  Worls widely. Most of these deaths are in Southeast Asia. In the United States about one hundred people die each other from snake bites.


Body Structure

(i) Snakes are elongated and lack limbs. Vestigial pelvic girdles and appendages are sometimes present.

(ii)They contain more than two hundred vertebrae and pairs of ribs. Joints between vertebrae make the body very flexible.

(iii) Snakes have adaptations in skull for swallowing large prey.Their upper jaws are moveable on the skull. The upper and lower jaws are loosely joined. Therefore, each half of the jaw can move  independently.

(iv) They have different mechanism for focusing the eyes and the morphologyof the retina than lizards.

(v) Their body is elongated and narrow. Therefore, left lung is reduced and gallbladder, right kidney and gonads are displaced.

(vi) Most snakes are oviparous. A few species give to live young like the New World boas and garter snakes.

Evolution of snakes

Zoologists debate the evolutionary origin of the snakes. The earliest fossils of snakes are 135-million-year-old Cretaceous period. Some zoologists believe that the earliest snakes were borrowers. Loss of appendages and changes in structure take place for borrowing habit. It is believed that early snakes were aquatic or they lived in denselyvegetated areas. Therefore, lost the legs.

(c)Suborder Amphisbaenia: Worm Lizards (amphi , douhle+boen, walk)

This order has about 13 species. They are specialized borrowers and live in soils. They are found in Africa, South America, the Carribean West Indies and the Middle East. Most of them are legles. Their skulls are wedge or shovel shaped.


A single median tooth is present in the upper jaw. It distinguishes amphisbaenians from all other vertebrates.The skin of amphisbaenians has ring like folds ,called annuli. Their skin in loosely attaches to the body wall. Skin bulges outward by the contraction of muscles. It forms an anchor against a burrow wall. Amphishaenians move easily forward and backward. Thus, they are named as amphisbeanians. They feed on worms and small insects. They are oviparous.

ORDER CROCODILIA (krokodeitos, lizard)

The order Crocodilia has 21 species. Dinosaurs and crocodilian, are derived from thearchosaurs. They has e certain special skull characteristics:

1. They have openings in the skull in front of the eve.

2. They have triangular eye orbits.

3. They have laterally compressed teeth.

Examples: Lining crocodilians are alligators, crocodiles, gavials and caimans.

Adaptations in crocodiles: Little changes take place in crocodilians over their 170-million year history.

(i) Snout: Their snout is elongated. It is used to capture prey by a sideways movement of the head. The nostrils are at the tips of the snout. Thus animal can breath mostly submerged.

(ii) Air passage way: Air passageways  open into rear of the mouth and throat. There is a flap of Tissue near the hack of the tongue. It forms a watertight seal. Therefore, breathing takes place without inhaling water in the mouth. The secondary palate us ohs ed in the archosaurs. Secondary palate is a plate of hone. It separates the nasal and mouth passageways.

(iii) Tail: Thev have muscular elongate and lateralk compressed tail. It is used or swimming. It is also used for offense and defense.

(iv) Digestive System: Teeth are used onlv for seizing prey. Food is swallowed as a whole. But crocodiles hold the large prey. It rotates it and tears it into small pieces a he stomach is gizzard like. The crocodilians swallow rocks and other objects. They use these rocks for breaking the ingested Food.

iv) Reproduction: Crocodilians are  oviparous. They  display parental care like birds. Nesting behavior and parental care shows that both birds and crocodiles have common ancestor.


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