Class Reptilia

Reptiles are the first class of organisms that adapt to life on land. They are generally to have evolved from the amphibians. They belongs to phylum Chordata of kingdom animalia.

Key Characteristics of Reptilia

Following are the common key characteristics of the Class Reptilia:

1. All reptiles are with Cleidoic eggs and Amniotic eggs (Shelled Eggs).
2. They having thick, rough and waterproof skin.
3. Presence of scales on their body is one of the key character in class Reptilia.
4. Reptiles having strong jaws for biting purpose.
5. As they belong to terrestrial animals Reptiles having more advanced respiratory organ system.
6. Heart is 3 chambered and having High-Pressure cardiovascular system except crocodiles. Crocodiles have a 4-chambered heart.
7. The body is distinctly divided into head, neck, and tail.
8. The presence of post anal tail is main character of class reptilia.
9. Excretion is generally Uricotelic for more water absorption.
10. Loop of Henle is well developed for maximum water absorption.
11. Metanephric kidney is present in all reptiles.
12. Their is only one occipital condyl present in the skull. i.e. monocondylic.
13. They are Ectothermic animals (Cold Blooded animals).
14. Fertilization takes place internally.
15. Sternum is greatly developed with ribs in reptiles.
16. Teeths in are generally homodont and polyphydont.
17. Shape of RBCs are oval and nucleated.
18. Their is no metamorphosis happens in reptiles.
19. Jacobson’s organ is present in only snakes as a sensory organ.

Classification of Reptilia

The class Reptilia is classified into four major sub-classes:

1. Anapsida
2. Parapsida
3. Diapsida
4. Synapsida

Anapsida

• These are sub-class of reptilia in which primitive reptiles are found with the skull roof.
• No Temporal openings are present.
• Sub-class Anapsida is further sub divided into two orders namely, Cotylosauria and Chelonia.
• Examples – Turtles and Tortoises.

Order Chelonia or Testudinata

• Body is short, broad and shape is oval.
• Clawed limbs are present with webbed or paddle like structure.
• Body encased in a firm shell or dorsal carapace and ventral plastron, made of dermal bony plates.
• Thoracic vertebrae and ribs usually fused to carapace.
• Skull anapsid, with a single nasal opening and without a parietal foramen. Quadrate is immovable.
• No sternum is found.
• Teeth absent. Jaws with horny sheaths.
• Cloacal aperture a longitudinal slit.
• Heart incompletely 4-chambered.
• Copulatory organ single and simple.

Diapsida

There are two temporal vacuities in the skull.
They are diverse of all reptiles.
The dinosaurs and pterosaurs are included in this group.
These are divided into two major groups- Archosauria and Lepidosauria.

Order Crocodilia

• Large sized, carnivorous and aquatic reptile.
• Tail long, strong and laterally compressed.
• Limbs short but powerful, clawed and webbed.
• Skin thick with scales bony plates and scutes.
• Skull diapsid. Quadrate immovable.
• No parietal foramen.
• A pseudopalate present.
• Ribs bicephalus. Abdominal ribs present.
• Teeth numerous, the codont, lodged in socket.
• Heart completely 4-chambered.
• Cloacal aperture is longitudinal slit.
• Male with a median, erectile, grooved penis.

Example – Crocodiles, Alligators, Caimans, Gavials, Chameleon.

Order Rynchocephalia

• 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 present. Quadrate is fixed.
• Vertebrae amphicoelous or biconcave.
• Numerous abdominal ribs present.
• Teeth acrodont.
• Cloacal aperture transverse.
• Heart incompletely 4-chambered
• No copulatory organ in male.

Example – Tuatara

Order Squamata

• Limbs clawed, absent in snakes and few lizards.
• Exoskeleton of horny epidermal scales.
• Skull diapsid. Quadrate movable.
• Vertebrae procoelous. Ribs single-headed.
• Teeth acrodont or pleurodont.
• Heart incompletely 4-chambered.
• Cloacal aperture is transverse.
• Male with hemipenis.

Example – Snakes and Lizards

Major differences between Snakes and Lizards

1. Lizards and snakes differ drastically in skull morphology. The skull bones of lizards tend to be tightly joined and stocky. Those of snakes tend to be elongated and mobile. This reflects their type of prey.
2. Most lizards are insect eaters and eat small prey, whereas snakes tend to eat vertebrate prey (lizards, small birds, mice) and they eat less frequently.
3. Snakes have one row of scales on the ventral surface, whereas lizards have many rows.
4. Lizards have external ear openings, which snakes lack.
5. Snakes focus by moving the lens relative to the retina of the eye.
6. Lizards have closing eyelids, snakes have a transparent eyelid that is fused closed.
7. Unlike lizards, the tails of snakes are short relative to their body.
8. Snakes have only one lung, one kidney, and the ovaries are packaged sequentially
9. Snakes have 160-400 vertebrae.

FAQs – Class Reptilia

References and Sources

• https://byjus.com/biology/reptilia/
• https://en.wikipedia.org/wiki/Reptile
• https://www.britannica.com/animal/reptile
• https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/reptilia

Further Readings

1. Chromosomal Aberration
2. Chromosome
3. Mendelian Inheritance
4. Phylum Chordata
5. Types of Chromosomes