Article: Pleromic dentine in a Permian crossopterygian fish (Family Osteolepidae)

Pleromic dentine is reported filling the pore-cavity spaces within the cosmine of the Early Permian rhipidistian fish Ectosteorhachis nitidus Cope (Family Osteolepidae). The pleromic tissue is only found in regions of specialized cosmine where the regular pattern of seasonal resorption and regeneration has broken down —a process that occurs in the later life history of members of this species. The functional significance of the pleromic tissue seems lo be mechanically to reinforce these regions of more permanent cosmine, with minimal loss of function in the pore-canal sensory system.