Whales are the biggest animals on Earth. They’re mammals, just like humans, and have a few things in common with us:
Most mammals live on land, so how did whales come to inhabit our oceans? Through evolution. Keep reading to learn more about the fascinating evolution of whales. You may be surprised by what you find out about the whale evolution timeline!
Whale Evolution: They Began on Land
In the period after dinosaurs became extinct and before humans appeared — or 50 million years ago to be more precise — lived a four-legged land mammal with cloven hooves, adapted for running. This creature, which resembled a large rat with long legs, is believed to be the first cetacean, or member of a group of aquatic mammals, such as whales and dolphins. It measured 3.2 to 6.5 feet long. Scientists named this early ancestor of today’s whales Pakicetus.
The discovery of skeletons in Pakistan revealed Pakicetus had a skull typical of cetaceans, and ankles typical of Artiodactyla. Artiodactyl refers to an animal that has hooves, and an even number of toes or digits on each foot, such as pigs, giraffes, and sheep. The shape of Pakicetus’ teeth also suggests it ate meat, just like some whales do today.
Whale Evolution Timeline: Transitioning Into an Aquatic Creature
It took about 8 million years for whales’ ancestors to evolve into mammals that live in water.
The permanent move to water, scientists theorize, began with some land mammals’ preference for eating plants that lay along shorelines. This location also offered them the benefit of easily slipping into the water to hide from threats, such as predators.
Over time, these mammals’ descendants spent more time in water and their bodies adapted to swimming: flippers evolved from front legs, and a thick layer of fat, or blubber, replaced their coats of hair to keep them warm and more streamlined in the water.
Nostrils became blowholes on the tops of their heads so they could breathe without needing to tilt their heads up while swimming. And while some of these animals began to eat a different diet, they lost their teeth and evolved into baleen filter feeders.
Their tails grew larger and more powerful for swimming, and their rear legs decreased in size. Whales began to swim by undulating their whole body, and resulting changes in their skeleton enabled their limbs to be used for steering, instead of paddling.
Whale Evolution: What Bones Tell Us
Cetaceans that are now extinct, such as Dorudon and Basilosaurus, revealed skeletal changes that accommodate life in the water. They had flexible elbow joints that were able to lock. This meant the forelimbs could better resist the oncoming flow of water as it propelled itself forward.
Some 47 million years ago, Ambulocetus, a four-legged whale that probably had webbed feet, was likely able to both walk and swim. Analysis of its bones has revealed it could live in both fresh and saltwater, and its inner ear was adapted to live in an aquatic environment.
Basilosaurus fossils also offer evidence of whales’ evolution. These ancestors had bodies that were more elongated than today’s whales. In addition, they had front flippers and small rear legs. Their nostrils sat midway between the snout and the forehead, and they had ear bones, just like those of modern-day whales.
In other words, Basilosaurus is what whales were at the midway point between their terrestrial ancestors and today’s whales.
The Two Major Groups of Whales
Today, there are two major groups of whales: odontocetes and mysticetes. Odontocetes are whales that have teeth, while mysticetes are also known as baleen whales or toothless whales. Both groups have a common ancestor that lived about 34 million years ago.
Whale species have diversified over 5 million years, which is likely the result of ecological changes in oceans. Cetacean species quickly diversified 15 million years ago, when ocean currents changed as a result of cooler water temperatures. At this time, the amount of mollusk and crustacean species that some whales consumed also increased.
Evolution of Whales: How They Became Giants
Whales reached the enormous size they are today roughly 4.5 million years ago. The earliest mysticetes were 16.4 feet to 29.5 feet in length. Their growth coincides with the climate growing colder and the formation of ice caps in the Northern Hemisphere.
Nutrients trapped in ice are released into the water in spring and summer and accumulate near coasts. Plankton — which whales eat — also accumulate in these areas and grow when they come into contact with nutrient-rich water. So, a greater amount of food and nutrients contributed to whales’ greater growth and size.
Is Whale Evolution Happening Today?
Science suggests whales began to evolve because their ancestors took advantage of their location: by the water, where they not only fed on plants but were able to quickly hide from danger by slipping under the waves.
Today’s whales face newer challenges, such as climate change, ocean pollution, and having enough food. (Blue whales, for example, eat up to 16 tons of plankton per day).
Yet, whales continue to evolve, as a result of changing ecosystems and dynamic interactions between species. If the eons have shown us anything, it’s that they’re adaptable creatures.
See and appreciate these awe-inspiring animals up close in Southern California. Witness a massive humpback whale breaching, admire the majesty of a blue whale, or delight in watching dolphins play. Book a whale-watching journey with Harbor Breeze Cruises today.
