Histologic Studies of Ostracoderms, Placoderms and Fossil Elasmobranchs 5. Ptyctodontid tooth plates and their bearing on holocephalan ancestry: the condition of chimaerids

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Abstract
A description is given of the histology and growth of the tooth plates in various fossil and recent chimaerids, with special reference to the structure of their vascular and compact pleromin. It is concluded that statodont elements of this kind cannot have had connection with the dentition of iniopterygians and cannot either have evolved from lyodont dental units of such bradyodonts as, for example, the cochliodontids. As compared with statodont elements in other fishes, the chimaerid tooth plates show resemblance in many ways to those of the ptyctodontids and may well have developed by certain structural changes from tooth plates like those of the latter.