Cosmine is a spongy, bony material that makes up the dentine-like layers in the scales of the lobe-finned fishes of the class Sarcopterygii.
[1] As traditionally described,[2] cosmine consists of a layer of dentine covered by a continuous sheet of enamel.
[3] Cosmine was first described in the Osteolepiform Megalichthys hibberti by Williamson in 1849, in a purely descriptive, pre-Darwinian, non-evolutionary framework.
Further descriptions of cosmine growth and development were advanced by Tor Ørvig,[6] dealing specifically with the pattern of squamation, or scale formation across the body of a fish.
Newer imaging studies[10] including synchrotron tomography show that pore canal systems in association with dentine occur outside the crown sarcopterygian clade, implying an older synapomorphy of Osteichthyes as opposed to a definitive sarcopterygian trait.