Q.Describe the exoskeleton and endoskeleton of reptiles.

[!TLDR] Reptiles have a dry, keratinised scaly exoskeleton (sometimes with bony plates) and a fully ossified endoskeleton. …

[!ANSWER] Reptiles show both an external (exoskeletal) and internal (endoskeletal) skeleton, both reflecting a fully terrestrial adaptation.

The reptilian exoskeleton is formed by the outer, keratinised layer of the epidermis, developed into dry, horny scales or plates covering the entire body. This dry, keratinised covering is a major adaptation for terrestrial life, since it dramatically reduces water loss through the skin compared with the moist, permeable, glandular skin of Amphibia. In some reptile groups, this basic scaly covering is reinforced by additional structures: turtles and tortoises develop a bony shell fused to the vertebral column and ribs beneath their outer scutes, and crocodilians develop bony plates (osteoderms) embedded in the skin beneath their scales, giving extra protection. …

• Confusing the reptilian scaly covering (a keratinised, epidermal exoskeleton) with true bony armour — only some groups (turtles, crocodiles) add bony reinforcement beneath it. …