Comparative embryology of Delphinapterus leucas (beluga whale), Balaena mysticetus (bowhead whale), and Stenella attenuata (pan-tropical spotted dolphin) (Cetacea: Mammalia)
Creator
Lia Gavazzi
Lisa N Cooper
Sharon Usip
Robert Suydam
Raphaela Stimmelmayr
John C George
Greg O'Corry-Crowe
Chih-Wei Hsu
Johannes Thewissen
Date
2023
Description
Embryogenesis of cetaceans (whales, dolphins, porpoises) is best known in Stenella attenuata, the pan-tropical spotted dolphin, based on a remarkably complete and well-studied prenatal ontogenetic series. Our study expands understanding of cetacean embryology by adding two additional cetacean taxa: the beluga whale (Delphinapterus leucas, Odontoceti), and the bowhead whale (Balaena mysticetus, Mysticeti). We identify key features that characterize these taxa at specific stages and highlight heterochrony between the odontocetes and mysticetes. The toothed whales are more similar in developmental timing to each other than either is to Balaena. The two odontocete taxa, Stenella and Delphinapterus, share similar developmental trajectories while early Balaena specimens differ from the odontocetes. This developmental variation proves challenging to ascribe to the existing Carnegie staging system. Most notably, flippers, hindlimbs, and flukes all provide morphological traits for characterization within the Carnegie staging system. A presomitic Delphinapterus embryo is also described. This study applies the Carnegie staging system to two more cetacean taxa and forms a framework for future research on cetacean developmental genetics and the modeling of fetal growth.
The prenatal development of bowhead whales is poorly known, and no complete ontogenetic series exist. However, the available embryos and fetuses elucidate aspects of the development of the species, as well as that of all of mysticetes in general, and demonstrate the role of heterochrony in development. For instance, hair on the face of bowhead whale embryos develops at the same ontogenetic stage as it does in terrestrial mammals, even though body hair never develops. The absence of teeth characterizes all modern baleen whales, but bowhead whale fetuses initiate teeth around the same time as land mammals, to then resorb them in the fetal period. Baleen forms after that, late in the fetal period.
The prenatal development of bowhead whales is poorly known, and no complete ontogenetic series exist. However, the available embryos and fetuses elucidate aspects of the development of the species, as well as that of all of mysticetes in general, and demonstrate the role of heterochrony in development. For instance, hair on the face of bowhead whale embryos develops at the same ontogenetic stage as it does in terrestrial mammals, even though body hair never develops. The absence of teeth characterizes all modern baleen whales, but bowhead whale fetuses initiate teeth around the same time as land mammals, to then resorb them in the fetal period. Baleen forms after that, late in the fetal period.