Cetacea (whales, dolphins, and porpoises) are mammals fully adapted to life in water so that some typical mammalian traits are not visible from their exterior appearance. The body of cetaceans is streamlined in shape. The head is connected to the body without a distinct neck so that it is merged to a single unit. The large boneless caudal fin (fluke) as the actual organ of locomotion is an evolutionary innovation. It is horizontally orientated and not vertical as in fishes or ichthyosaurs. Accordingly, spine and trunk muscles of cetaceans are designed primarily for dorsoventral movements. Moreover, a boneless connective tissue formation represents the unpaired dorsal fin. Flippers (forelimbs) and dorsal fin only control and stabilize the body’s position while swimming.
The Origin of Modern Cetaceans
At the end of the last century, the knowledge about cetacean fossils was so sparse that one could not be sure what the ancestors of the cetaceans looked like. During the last 25 years,...
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