• Cosmoid scale

Cosmoid scales are a special type of scale found in some fossil bony fishes, bipedal fishes, many cysteopterygians, and modern latima. Cosmoid scales are fused and highly modified placoid scales. The scales of present-day latimeria have 4 layers: superficial with denticles; spongy-bony; bony-spongy; and the lower layer consisting of bony plates.

The scales of ancient coelenterate and bipedal fishes, the outer surface of which is formed by a layer of cosmina (hence the name), a continuous "parquet" of closely interlocked cutaneous teeth. From above, cosmoid scales are covered with hard enamel-like dentin, giving it a characteristic shine. The cosmine is underlain by a layer of spongy bone; at the base of the cosmoid scale lies a thick layer of lamellar bone, the isopedine. The outer and spongy layers of the cosmoid scale gradually reduced in the evolution of kysteipterous and bipedal fishes. In the modern cysteopteran fish Latimeria individual dentin tubercles are preserved on the surface of the scales.

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Cosmoid scale

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