General Characteristics Class Reptilia

General Characteristics:

1. General Overview: Reptiles include about 9,500 species such as lizards, snakes, turtles, tortoises, and crocodiles. They dominated the Earth around 200 million years ago during the Jurassic period of the Mesozoic Era, also called the Golden Age of Reptiles. Reptiles are primarily terrestrial, although some species (e.g., tortoises, crocodiles) live in water.
2. Body Structure: Reptiles have a body that can be long and cylindrical or short and broad, divided into head, neck, trunk, and tail. The skin is dry, rough, non-glandular, and covered with horny, epidermal scales. They have pentadactyl limbs (five digits) with horny claws used for locomotion, though some reptiles, like snakes, lack limbs.
3. Endoskeleton: The endoskeleton is bony and provides structural support. The skull is monoconidylic, meaning it articulates with the vertebral column through a single occipital condyle.
4. Digestive System: The digestive system is well developed, with a large mouth equipped with acrodont teeth (teeth attached directly to the jawbone). Reptiles can swallow large prey due to movable jaw bones.
5. Respiratory System: Lungs are the primary respiratory organs, and ribs assist in expanding and contracting the body cavity for efficient breathing. Some reptiles, like turtles, can also perform cloacal respiration.
6. Circulatory System: Reptiles generally have a three-chambered heart (two auricles and one ventricle), but crocodiles have a four-chambered heart. The ventricle in most reptiles is incompletely divided by a septum. RBCs are oval, biconvex, and nucleated.
7. Excretion: Kidneys are the primary excretory organs. Land-dwelling reptiles are uricotelic (excrete uric acid), while aquatic reptiles are ureotelic (excrete urea).
8. Nervous System: The nervous system includes 12 pairs of cranial nerves, and sense organs like eyes, ears, and nose are well developed. Reptiles have excellent vision, hearing, and smell.
9. Temperature Regulation: Reptiles are cold-blooded (poikilothermic) animals, meaning they cannot regulate their body temperature internally. They undergo hibernation during cold seasons. Snakes and lizards periodically shed their skin (called ecdysis or skin cast).
10. Reproduction: Reptiles are unisexual and exhibit sexual dimorphism. Fertilization is internal, and most reptiles are oviparous (egg-laying). Some species, like vipers and sea snakes, are ovoviviparous, meaning they retain eggs inside the mother's body, and the embryos develop there. Development is direct, with no larval stage.

Examples of Class Reptilia: Lizards: Calotes (garden lizard). Draco (flying lizard). Chameleon (arboreal lizard). Hemidactylus (wall lizard). Crocodilians: Crocodilus (crocodile). Alligator (alligator). Tuatara: Sphenodon (living fossil). Snakes: Naja (cobra). Bungarus (krait). Vipera (viper).Turtle (Chelone), Tortoise (Testudo), Garden Lizard (Calotes), Tree Lizard (Chameleon), Wall Lizard (Hemidactylus flaviviridis), Limbless Lizard (Ophisaurus), Desert Lizard (Phrynosoma), Flying Lizard / Flying Dragon (Draco), Crocodile (Crocodilus), Alligator (Alligator), Krait (Bungarus), Viper (Vipera), Cobra (Naja naja), Blind Snake (Typhlops), Sea Snake (Hydrophis)