Class Reptilia

Class Reptilia

Reptiles are the first class of chordates, among those covered in this chapter, to be fully independent of an aquatic larval stage, showing direct development and full adaptation to terrestrial life (though many reptile groups have secondarily returned to aquatic habitats).

Exoskeleton — the reptilian body is covered externally by dry, keratinised (horny) epidermal scales or plates, which form a protective, water-resistant covering that greatly reduces water loss through the skin — an important adaptation for a fully terrestrial existence, and a marked departure from the moist, glandular, permeable skin of Amphibia. In some reptile groups (turtles, crocodiles) this exoskeleton is further reinforced by underlying bony plates.

Endoskeleton — the reptilian endoskeleton is a fully ossified (bony) skeleton, generally more robust than that of Amphibia, and includes further terrestrial adaptations depending on the group (e.g. limb structure adapted for efficient walking/running rather than the amphibian's leaping gait).

Orders of Reptilia, with two examples of each:

• Order Chelonia (Testudines) — the turtles and tortoises, distinguished by a bony shell fused to the vertebral column and ribs; examples: Testudo (tortoise), Chelone (marine turtle).
• Order Crocodilia — large, predominantly aquatic reptiles with an elongated snout and a heart that is nearly completely four-chambered; examples: Crocodylus (crocodile), Alligator (alligator). …