Question

The crossopterygians possess scales called as

• A. Placoid
• B. Cycloid
• C. Ganoid
• D. Cosmoid

Answer 1

The correct option is D Cosmoid

Cosmine is present in the scales and dermal bones of all primitive crossopterygians. This is often lost in more advanced forms. The scales of most crossopterygian groups are characteristic. Primitive members have thick, cosmine-covered rhombic scales. The scales of both groups changed from rhombic to round, lacking cosmine, in their radiations. The rhizodontiforms, onychodontiforms and actinistians have thinner, rounded scales. Crossopterygians have well developed sensory line systems, visible as a series of pores and pit-line canals on the dermal bones and scales.