Class Reptilia

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🐍 Class Reptilia

Reptiles were the first vertebrates to fully adapt to life on land by developing amniotic eggs, which protect and nourish the embryo outside of water.

🥚 Amniotic Egg

  • Reptiles possess amniotic eggs that have protective extra-embryonic membranes:

    • Amnion – surrounds and protects the embryo.

    • Allantois – stores waste and helps in gas exchange.

    • Chorion – surrounds all membranes and aids in respiration.

  • These membranes prevent drying, nourish the embryo, and enable development on land.

  • The egg contains a large amount of yolk, serving as the primary food supply for the embryo.

  • Albumin provides extra nutrients and water.

  • The egg is covered by a leathery or calcareous shell — permeable to gases but not to water.

🦴 Body Structure

  • Reptiles have dry, scaly skin, which prevents water loss.

  • The bony endoskeleton is stronger and harder than that of amphibians.

  • The skull is longer, providing better jaw movement.

  • The first two cervical vertebrae (the atlas and axis) allow greater head movement.

❤️ Circulatory and Thermoregulation

  • The heart has two atria and a partially divided ventricle, allowing some separation of oxygenated and deoxygenated blood.

  • Reptiles are ectothermic (cold-blooded) — they depend on external heat sources for body temperature regulation.

  • They are poikilothermic, meaning their body temperature varies with the environment.

🐣 Reproduction

  • Fertilization is internal.

  • Most reptiles are oviparous (egg-laying).

🐊 Examples

  • Lizards, Snakes, Tuatara, Crocodiles



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