dermal scale

In zoology, a scale is a small plate or shield that forms part of the outer skin layers of certain animals, primarily providing protection.1

Types of Scales

• Dermal Scales: These are bony plates originating from the deeper dermal layer of the skin. They are abundant in fish, such as the placoid scales of sharks, which are spiny projections with an enamel-like covering. Ganoid scales, found on gars and bowfin, are similar but covered in ganoin. Advanced fish have cycloid scales (round or oval with growth rings) or ctenoid scales (similar to cycloid but with comblike teeth). Turtles also have bony dermal scales called osteoderms beneath their external scales.123
• Epidermal Scales: These are horny, tough extensions of the outer skin layer (epidermis). They are well-developed in reptiles and are also found on the skin of birds and mammals. Bird feathers are considered modified epidermal scales, and the scaly surfaces on some mammals, like pangolins, are also modified epidermal tissue, primarily keratin.13

While fish and reptiles commonly possess dermal scales, birds and mammals have largely reduced dermal derivatives, with a greater emphasis on epidermal extensions like feathers and hair.4