Scaliness

Scaliness is the quality of being covered with scales, a feature seen in several animal groups. Scales are protective plates that form part of the skin’s outer covering. The term denotes a range of structures with different developmental origins, most notably in fishes, reptiles, and certain mammals such as pangolins and armadillos.

In bony fishes, scales are dermal in origin and lie under a thin outer layer. Teleosts typically have cycloid or ctenoid scales, while some early ray-finned fishes possess ganoid scales. Scales grow with the animal and provide abrasion protection; they can also influence hydrodynamics and camouflage.

Reptile scales are keratinous, formed from the epidermis and often arranged in overlapping patterns. They protect against injury and water loss, and in turtles can form large scutes. Snakes and lizards show diverse scale shapes and sizes, and many reptiles shed or replace scales as part of growth.

Among mammals, scaliness is rare but present in a few groups. Pangolins wear overlapping keratinized scales, serving as armor. Armadillos have bony osteoderms beneath a keratinized skin that forms armor plates. These structures illustrate convergent evolution toward protective coverings rather than a single shared ancestry for all scaliness.

Overall, scaliness is an adaptive trait linked to habitat, moisture regulation, and protection. The tissue origin, microstructure, and patterns of scales vary widely among lineages, reflecting distinct evolutionary paths while maintaining a common protective function.