The group in question—the cetaceans (whales, dolphins and porpoises)—are introduced at this point because, despite appearances, they are close kin to the artiodactyls. Closer kin, in fact, than the perissodactyls (odd-toed ungulates) are to the artiodactyls. Simply put, this means that cattle (artiodactyls) are closer cousins to whales (cetaceans) than they are to horses (perissodactyls).
Now, you may have noticed that cetaceans don't look a whole lot like your average artiodactyl (cow, hippo, deer, antelope, camel, pig, and so forth). Not only do they lack hooves, legs and feet, cetaceans aren't even herbivores like most artiodactyls. Instead, they are among the most impressive carnivores in the world. The baleen whales, which include the largest animal that has ever lived (the blue whale), filter vast quantities of krill (a type of crustacean) from the sea. Toothed whales feed on prey that includes fish, squid and (in the case of orcas) sea lions and other mammals.
Yet despite many obvious differences between modern-day cetaceans and artiodactyls, the two groups are thought to be linked by a common ancestor that lived about 60 million years ago. The earliest whales, known as the archaeocetes, are thought to have been most closely related to the artiodactyl lineage that produced the hippopotamuses. Early whales included creatures such as Pakicetus, Indohyus, Rodhocetus and Zygorhiza.
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