Abstract Here we describe the stages of tooth development in toothed whales on the basis of the harbor porpoise ( Phocoena phocoena ). The aim of the study was to find out whether these stages are identical to those of other mammals analyzed so far although toothed whales are homodont and monophyodont. We used the collection of histological specimens of embryos and fetuses (51–167 mm total length). The first signs of tooth development were an epithelial thickening, during which the epithelium of the oral cavity thickened by forming several cell layers. Following this, a dental placode was formed which represented an ingrowth of the epithelium into the mesenchyme. From this placode an elongated structure was formed called dental lamina. At its deepest margin, a round structure represented the bud stage which was followed by the cap stage. In the course of further cell proliferation, this cap expanded to the bell stage, in which all tissues required for the formation of a tooth were present. The examination of a post‐natal specimen (skull length 167 mm) showed that the teeth were lined up along a common dental groove and the teeth's length decreased from mesial to distal. However, a presumed stage sequence—mesial more advanced stages than distal—could not be observed in the embryos and fetuses. The results of this study give the first complete photographical documentation of tooth development in toothed whales and, thus, the first coherent developmental process description showing that it followed the same stages as in other mammals.
Mathes et al. (Fri,) studied this question.