Embryology of dolphins. Staging and ageing of embryos and fetuses of some cetaceans.

Comparative embryology has been neglected in the past decades. In our opinion the decreased interest has been caused by the fact that the time factor has not sufficiently been respected. Therefore we used the Staging and Ageing Method (Stĕrba 1999) to determine the ontogenetic age of embryos and to state the time tables and time relations of various ontogenetic events. We examined 167 embryos and fetuses of four dolphin species (collection Dr. Senckenbergische Anatomie, Frankfurt am Main). The study of intrauterine development and growth while consistently respecting the time factor enabled us to determine the time course of organogenesis of all organ systems. The resulting comparison with other mammals detected the time lag in ossification, retardation of odontogeny, the time of the origin and development of the fluke, dorsal fin and flipper, etc. We believe the Staging and Ageing Method serves for a much more efficient evaluation of existing embryological collections which very often contain embryos of unknown age.