Palaeohistological Notes

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Abstract
Ørvig, T. (Section of Palaeozoology, Swedish Museum of Natural History, S‐104 05 Stockholm, Sweden.) Palaeohistological notes. 4. The interpretation of osteodentine, with remarks on the dentition in the Devonian dipnoan Griphognathus. Zool. Scr. 5 (2): 79–96, 1976.—A renewed discussion of the ontogeny and structure of osteodentine (“trabecular dentine”) reaffirms the writer's earlier conclusions that this hard tissue forms initially as a system of bony trabeculae and achieves its final character of dentine by the development of denteons (instead of, as in bone tissue, osteons) on the margins of these trabeculae. In this connection remarks are given on the hard tissue surrounding the tritural columns of the tooth plates in various fossil and recent holocephalans. Osteodentine differs in conditions of mineralization, fibrous texture and growth from the vascular pleromin (pleromic hard tissue) of many dipnoan tooth plates with which it has on occasion been confused. In the Devonian dipnoan Griphognathus, the dentition is in certain respects suggestive of that in some elasmobranchs. — In connection with this paper, methods of investigating fossil hard tissue by the SEM are discussed.