Class Reptilia

Reptiles are animals that have adapted to life on land. Unlike amphibians, reptiles have special adaptations that allow them to thrive in dry environments. They are well-suited for terrestrial life because they have amniotic eggs and dry, scaly skin, which protect them from dehydration.

Key Characteristics of Reptiles:

1. Special Feature – Amniotic Eggs:
   • Reptiles lay amniotic eggs, which have extra-embryonic membranes: the amnion, allantois, and chorion. These membranes provide important functions for the developing embryo:
     • Amnion: Protects the embryo by creating a watery environment around it.
     • Allantois: Helps with gas exchange and waste removal.
     • Chorion: Helps protect the embryo from drying out and plays a role in gas exchange.
   • These membranes are a significant evolutionary adaptation that allowed reptiles to move away from water and live on land.
2. Yolk:
   • The yolk in the egg provides the primary food supply for the developing embryo, ensuring it has enough nutrients to grow before hatching.
3. Albumin:
   • The albumin in the egg surrounds the yolk and provides additional nutrients and water to the developing embryo.
4. Egg Shell:
   • The egg shell is leathery or calcareous (made of calcium) and is permeable to gases (like oxygen and carbon dioxide) but not to water. This helps protect the embryo from drying out while still allowing it to exchange gases with the environment.
5. Skin:
   • Reptiles have dry, scaly skin. The scales are made of keratin, which is a tough, waterproof material. This helps prevent water loss and allows reptiles to live in dry environments.
6. Skeleton:
   • Like amphibians, reptiles have a bony endoskeleton. However, their bones are generally harder and more rigid than amphibians, which helps them support their larger bodies on land.
7. Skull:
   • Reptiles typically have a longer skull than amphibians. This allows them to accommodate larger brains and more developed sensory systems.
8. Neck Movement:
   • The first two cervical vertebrae (the atlas and axis) in reptiles are specialized to allow for greater head movement. This is a major advantage for reptiles, allowing them to turn their heads in various directions, which is especially important for predators.
9. Heart:
   • Reptiles have an incompletely partitioned ventricle. This means their heart has three chambers: two atria (upper chambers) and one ventricle (lower chamber). However, there is some mixing of oxygenated and deoxygenated blood because the ventricle is not fully separated.
10. Body Temperature:

• Like amphibians, reptiles are ectothermic and poikilothermic, meaning they depend on external heat sources (like the sun) to regulate their body temperature, and their body temperature can fluctuate based on the environment.

11. Reproduction:

• Reptiles reproduce through internal fertilization, meaning that the male deposits sperm inside the female’s body. Most reptiles are oviparous, meaning they lay eggs. Some reptiles, like certain species of snakes, give birth to live young (this is called viviparity).

12. Examples of Reptiles:

• Lizards and snakes: These animals are known for their scaly skin and ability to slither or run on land.
• Tuatara: A unique reptile from New Zealand that looks like a lizard but belongs to a distinct group called Rhynchocephalia.
• Crocodiles: Large, powerful reptiles that live in freshwater and saltwater environments.

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Mnemonics for Reptilia:

• “A Great Snake Can Have Scales”
  • A = Amniotic egg
  • G = Great skull (longer skull)
  • S = Scaly skin
  • C = Cervical vertebrae (neck movement)
  • H = Heart with 3 chambers
  • S = Special features (leathery eggs)

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Summary of Differences Between Amphibians and Reptiles:

• Amphibians are moist-skinned, rely on external fertilization, and have a three-chambered heart. They need water to reproduce and undergo metamorphosis.
• Reptiles have dry, scaly skin, lay amniotic eggs, and have a three-chambered heart (with some exceptions). They can reproduce on land and are better adapted for dry environments.