Ausgangsform und Entwicklung der rhombischen Schuppen der Osteichthyes (Pisces)

Ganoid and cosmoid scales, the two types of rhombic scales within the osteichthyans, can be traced back to a primitive scale similar to the scales ofLophosteus. The primitive rhombic scale did not have a peg-and-socket articulation, it is composed of lamellar bone superposed by many layers of spongy bone + dentine. That kind of superposition of layers of spongy bone + dentine (+ enamel) has been retained in the cosmoid scale; in contrast in the ganoid scale the growth of the dentine has become restricted to the lateral surface, the growth of ganoin to the outer surface and the growth of bone to the inner surface of the scale. The scales ofAndreolepis have a position between the primitive rhombic scale and the ganoid scale. — Scales from the Gedinnian (Lower Devonian) of New Sibirian Islands, USSR, are described asDialipina markae n. sp. The morphological features are very typical for the genus, but the histology is different from the type speciesD. salgueiroensis. Within the two Devonian palaeoniscoid generaDialipina andOrvikuina acellular bone with irregular non-vascular canals of Williamson has developed twice from cellular bone.