Teeth from Recent adult and juvenile Somniosus microcephalus were inspected and compared with 9 very rare fossil teeth found in the Lower and Upper Pliocene sediments of Antwerp/Kallo (Belgium). This material shows that the teeth of the lower jaw from juvenile specimens are provided with smooth cutting edges. At a certain age of the fish and size of the tooth, however, fine serrations develop on the cutting edges. When a shark grows older, the teeth increase in size and in most cases also the prey. This requires a longer cutting edge to sever the food tissue. A serrated cutting edge will allow the shark to produce lower crowns, due to the more effective severence in most tissues, than smooth ones. Serrated cutting edges also remain sharper for a longer period of time. Sharks invest a certain amount of energy in their continual tooth replacement process. The positive result in relation to the development of smaller serrated teeth, is a reduced energy consumption towards tooth replacement and therefore an increased chance to survive. The only available fossil tooth from the upper jaw has an intact crown with smooth cutting edges which resembles the Recent S. microcephalus. However, the root has weathered to such an extent that comparison with Recent teeth is not possible anymore. The fossil teeth from the lowerjaw are compared with recent specimens of the same dimensions. They are all serrated and between 14-17 mm tall. They have belonged to adult sharks with an estimated length of 450-550cm. - In general the crowns of the Recent teeth are in relation to the root of lesser height. - The fossil teeth are between apron and uvula thicker (3-4mm) than the Recent specimens (2 mm and in one case 2.5 mm). The crown of the fossil teeth are therefore more convex and the roots show more pronounced foramina, ducts and folds. - The fossil teeth show clearer serrated cutting edges.

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Grondboor & Hamer

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Nederlandse Geologische Vereniging

W. van der Brugghen. (1992). Over recente en fossiele tanden van de haai Somniosus microcephalus. Grondboor & Hamer, 46(1), 12–16.