General Characteristics and Classification of Reptilia

 

General Characteristics of Reptilia

Reptiles belong to the class Reptilia under the subphylum Vertebrata of the phylum Chordata. They are cold-blooded (ectothermic) vertebrates that are primarily terrestrial and possess adaptations for survival in dry environments.

Characteristics:

1. Body Structure: Reptiles have a triploblastic, bilaterally symmetrical, and coelomate body with a tough, scaly skin that reduces water loss.
2. Exoskeleton: Covered with epidermal scales or scutes made of keratin. These scales provide protection against desiccation and predators.
3. Respiration: Respiration occurs through lungs throughout their life cycle.
4. Circulatory System: They possess a three-chambered heart (except crocodiles, which have a four-chambered heart) and a double circulatory system.
5. Thermoregulation: Reptiles are ectothermic and rely on external sources for body temperature regulation.
6. Excretion: The excretory system consists of metanephric kidneys, and they excrete uric acid to conserve water.
7. Reproduction: Mostly oviparous (egg-laying), but some are ovoviviparous or viviparous. Fertilization is internal. Eggs have calcareous or leathery shells that protect the developing embryo.
8. Nervous System: Well-developed brain and 12 pairs of cranial nerves.

9.      Skeletal System: Well-ossified endoskeleton with vertebrae, ribs, and a sternum. Limbs are usually pentadactyl (five-fingered) but may be absent in snakes.

10. Locomotion: Different modes of movement, including walking, running, burrowing, swimming, and climbing.
11. Sensory Organs: Well-developed eyes, Jacobson’s organ (for chemoreception), and external ear openings (except in snakes).

Classification of Reptilia (Up to Order Level)

Class Reptilia is classified into four major orders:

1. Order Rhynchocephalia (Tuatara)

1. Primitive reptiles with lizard-like appearance.
2. Only one extant species, Sphenodon punctatus (Tuatara), found in New Zealand.
3. Skull with diapsid condition (two temporal openings).
4. Parietal (third) eye present on the head.
5. No external ears.

2. Order Squamata (Lizards and Snakes)

1. Largest order of reptiles, including lizards and snakes.
2. Movable quadrate bone allows for wide jaw opening in snakes.
3. Skin shed periodically.
4. Suborders:

3. Order Testudines (Chelonia – Turtles and Tortoises)

1. Body enclosed in a bony shell (carapace on top, plastron on the bottom).
2. Limbs adapted for swimming (turtles) or walking (tortoises).
3. Toothless jaws covered by a horny beak.
4. Examples: Chelone (Sea turtle), Testudo (Tortoise), Trionyx (Softshell turtle).

4. Order Crocodylia (Crocodiles, Alligators, and Gharials)

1. Largest and most advanced reptiles.
2. Four-chambered heart, unlike other reptiles.
3. Strong, laterally compressed tails for swimming.
4. Teeth are thecodont (embedded in sockets).
5. Examples: Crocodylus (Crocodile), Alligator, Gavialis (Gharial).

References

1. Hickman, C. P., Roberts, L. S., Keen, S. L., Larson, A., I'Anson, H., & Eisenhour, D. J. (2017). Integrated Principles of Zoology (17th ed.). McGraw-Hill Education.
2. Pough, F. H., Janis, C. M., & Heiser, J. B. (2018). Vertebrate Life (10th ed.). Oxford University Press.
3. Romer, A. S., & Parsons, T. S. (1986). The Vertebrate Body. Saunders College Publishing.
4. Goin, C. J., Goin, O. B., & Zug, G. R. (1978). Introduction to Herpetology (3rd ed.). W. H. Freeman & Company.