Variability in Techniques of Counting Dentinal Growth Layer Groups in a Tooth of a Known-Age Dolphin, Tursiops truncatus

A photograph of a mid-longitudinal tooth section of a known-age bottlenose dolphin was used to evaluate the techniques of six experienced tooth readers in counting the growth layer groups (GLGs). The results point up the problem of using different criteria to define GLGs. When age is known, GLG counts may be similar even if somewhat different landmarks in the tissue are used. However, when age is unknown, GLG definitions tend to be more variable among readers using different criteria. The results of the present exercise suggest a critical need to intercalibrate the various aging techniques for given species