The small bony or horny plates that form the body covering of reptiles
| Ganoid scales of the Florida gar
There are four main kinds of scales in fish:
These are found in sharks and rays, and can vary greatly in appearance.
They don't increase in size as the fish grows; instead new scales are
added. Placoid scales consist of a flattened rectangular base plate
which is embedded in the fish, and variously developed structures, such
as spines, which project backwards on the surface.
These are found in lungfish and some
fossil fishes. Cosmoid scales are similar to placoid scales and probably
evolved from the fusion of placoid scales. They consist of two basal
layers of bone, a layer of dentine-like cosmine, and an outer layer
These are found in fishes such as the bichirs, bowfin, paddlefish, gars,
and sturgeons. Ganoid scales are usually rhomboid in shape and have
articulating peg and socket joints between them.
- Cycloid and ctenoid
Cycloid and ctenoid scales are found in the majority of bony fishes.
The anterior part of each scale is usually overlapped by the posterior
portion of the scale in front. This arrangement of overlapping scales
gives the fish greater flexibility than in those species with cosmoid
and ganoid scales.
Unlike fish scales, reptile scales are not separate, detachable structures.
Instead, they are connected in a sheet, which is the outermost layer of
skin. Every so often, this layer of skin is shed and replaced. In some reptiles
the skin flakes off in chunks. In snakes, the skin is usually shed in one
piece. Reptilian scales are of two types: horny epidermal corneoscutes sometimes
fused with underlying bony dermal osteoscutes.