From Feet to Flippers
Whales and dolphins are beloved animals in many places around the world. From their intelligence and sociability to their sheer enormity, many people are fascinated by the mysterious underwater lives of these majestic creatures. Despite growing curiosity, many people are surprised to discover that whales evolved from land mammals. Cetaceans – the group of animals which includes whales, dolphins, and porpoises – evolved from a group called the artiodactyls, or even-toed ungulates. Artiodactyls are hooved animals that bear weight evenly on two toes. Of the artiodactyls alive today, the whale’s the closest relative is the hippopotamus.
It may be difficult to imagine a whale sauntering about on land, but modern cetaceans are not the artiodactyls of 50 million years ago. Whales evolved from a creature called Pakicetus – a wolf-sized furry animal with hooves, a tail and a long snout. Unlike today’s whales, Pakicetus had nostrils on the tips of its nose (not the back of the head), and no fins. This ancient furball would have had a difficult time taking down a giant squid like today’s sperm whales!
While there is some evidence for Pakicetus being semi-aquatic (such as dense leg bones to ease walking in rivers), this furry, finless wolf-creature spent much of its life on land. Over time, natural selection favoured individuals with traits that allowed them to spend more time in the water. Scientists are uncertain whether it was predators, prey, habitat, or something entirely different that pushed them to evolve into aquatic environments.
Whales have changed dramatically from their early ancestors, but there are still many clues in the skeletons of modern whales that show us where they come from. Based on its skeleton alone, a whale is more closely related to a mammal like you than it is to any fish. The bones that make up the pectoral flippers contain the exact same bones as the ones in your arms and hands. They occur in different proportions, but whales and humans (and bats and cats and hippos) have a humerus, radius, ulna, carpals, metacarpals, and phalanges.
Likewise, the movement of a whale’s skeleton as it swims through the water hints at its evolution. Fish swim by swishing their tails side-to-side in a horizontal motion. Cetaceans pump their tails up and down to move through water. This vertical motion is made with the same spinal movement of a galloping terrestrial quadruped, such as a horse or a deer. In other words, whales are essentially galloping underwater!
If you would like to learn more about how whales evolved, check out these resources: