ABSTRACT
The prenatal development of most species of cetaceans is poorly known because descriptions were based on fortuitous recoveries of one or a few embryos of one species, and it was impossible to acquire complete ontogenetic series. However, these occasional and inconsistent discoveries have played an important role in the development of the biological sciences. For instance, the discovery that dolphins have hind limb buds was initially controversial (Kükenthal 1893, 1895; Guldberg 1894, 1899); however, they served to boost the nascent evolutionary theory which had been interested in whale evolution since its origin (Darwin 1859, p. 450-456). At present, the best-studied embryological collection of cetaceans is located at the Senckenbergische Anatomie of the Wolfgang Goethe Universität in Frankfurt, Germany. Many recent studies of cetacean embryology are based on this collection (references by Klima and Oelschläger and co-workers), and it has spawned a new interest in theoretical works into broader evolutionary topics, such as developmental control in evolution (Bejder and Hall 2002; Thewissen and Williams 2002). In spite of its great importance, most species of cetaceans in the Frankfurt collection are represented by only a few specimens. A relatively complete ontogenetic series for three delphinid species in the Frankfurt Collection was described by Šterba et al. (2000). These authors divided embryonic and early fetal dolphin development into twelve stages using criteria originally designed for staging land mammal embryos. However, Šterba et al. (2000) did not have material documenting the earliest stages of development (their Stages
1 and 2), leading them to make assumptions about probable morphologies of early embryos. Although very useful as a descriptive study, Šterba’s et al.’s (2000) work is also idiosyncratic. Several of their stages are defined on the basis of characteristics not present in cetaceans (such as Stage 11: haircoat all over body), making objective characterization of these stages impossible. Furthermore, Šterba et al. (2000) rigidly apply their numbering system to the delphinids even though heterochronic events in cetacean evolution have altered the order in which key characters appear in ontogeny. As a result, the sequence of numbers is counterintuitive: Stage 12 occurs between Stage 9 and 10 in developmental time.
