All creatures on this planet are somewhat related. We humans even share a common ancestor with sharks; sure, it lived more than 400 million years ago, but it does make sharks our distant cousins. Let's say you were asked to guess what a whale's closest relative was. Your first answer might be dolphins or even salmon; well, you'd be wrong. Hippos are, in fact, the closest to whales on the family tree.
It's not the only weird aspect of whale evolution. Take these two types of creatures: whales and hippos. Even though they share some similarities, like being big and loving the water, they didn't get those traits from the same place. They seem to have evolved these features separately, like twins who dress alike by coincidence. We know this because hippos have ancient relatives called anthiotheus, which weren't that big and didn't enjoy the water.
You'd expect the ancient whale relatives, like pakicetus, for instance, to be very big fans of water. You'd be wrong again. They were more like typical land animals with features like long skulls and sharp teeth, perfect for eating meat. However, when you peek inside their heads, particularly in the inner ear region, things start to match up with today's whales.
Following the branches of the whale family tree, we'll then meet ambulocetus. This creature seems to have taken a more aquatic turn in life. It had shorter legs, plus its hands and feet started looking like paddles, perfect for a swim. Its long muscular tail and the location where its fossils were found also indicate it enjoyed water a bit more than its ancestors. It seems it spent time in estuaries or bays, which are places known for their mixture of saltwater and freshwater. These days, we can even check what creatures used to drink back then by looking at the oxygen isotopes in their bones, and it turns out that ambulocetus sipped on both saltwater and freshwater.
The story goes on with even more aquatic pre-whales. They had nostrils that shifted further back on their snouts, which eventually led to the blowhole on the top of their heads. Their pelvis saw some adjustments over the years too; it started to shrink and attach from the backbone since legs weren't particularly needed anymore. This new feature allowed their whole body to move more easily in the water.
You've probably seen dolphins or whales swim; their tails go up and down, not side to side like fish. That's because they evolved from land mammals whose backbones weren't built for wiggling side to side. As they transitioned to undulating swimmers, their limbs started to become better for steering rather than paddling. Watch dolphins or whales swim, and you'll notice their tail fins are horizontal, not vertical like fishes. This helped them steer with their entire bodies, not just their tails.
Through more fossil records, we find other ancient whales with clear adaptations for aquatic life, including a tail fluke that could power their swimming. Their elbow joints were flexible and able to lock, giving their front limbs great control over surfaces in the water. Their hind limbs, however, became tiny and almost useless. In fact, sometimes we might even see vestiges of these tiny hind limbs in living whales, but they don't do much. Either way, these hind limbs are proof of their land-dwelling past.
What also makes whales unique is the fact that some of them became the biggest animals in the world. The Antarctic blue whale can weigh as much as 33 elephants and can reach the lengths of a 10-story building. So how did some whales evolve to reach these impressive measurements?
Traveling back in time after the dinosaurs disappeared, we'll notice massive mammals started to dominate the land. But in the ocean, whales took their time to become giants, and that might be why they're still the kings of the sea today. Researchers at the University of California did a study on this. They checked the fossil record and found some fascinating information about how ocean giants evolved over the past 34 million years. They found that these large creatures have a different story than big land animals. For instance, whales only started getting enormous about 5.3 million years ago during a period called the Miocene-Pliocene transition. On the other hand, the largest land mammal, a relative of the rhino called paraceratherium, became massive way sooner, about 30 million years ago.
Something surely must have held whales back from becoming massive until quite recently in geological terms. They couldn't puff up like the land mammals did. Usually, how big an animal gets depends on its food source. Here's where the whales lost the bet, in evolutionary terms at least. Big as they are, they aren't the top predators. They eat tiny creatures like krill, and how much krill they get to eat depends on how much the ocean produces. Whales got really good at filter-feeding, which is like dining with a built-in sieve. Back in the Eocene period, whale experts believe this to be significant because something must have changed in the ocean to give them more or different types of food.
Researchers believe this giant growth spurt could be linked to a super-productive ocean around 2.5 million years ago during the Pliocene. This is when huge ice sheets were grinding rocks into nutrient-rich particles that flowed into the sea. That would have transformed our planet's oceans into huge buffets for whales. Others think it might not just be about how much food there was but how it was spread out. If the buffet tables were far apart, you'd want to be big enough to travel between them efficiently. A larger body also means more food storage for energy. So, a modern productive ocean that might have been patchy probably pushed these whales to bulk up.
All this information matters not just to satisfy our curiosity. Big animals like whales, elephants, and lions have a huge impact on their environments. Despite their lower numbers, elephants, for instance, help fertilize important trees. As the planet continues to change, these giant marine mammals might struggle, maybe having to find new feeding spots or facing the risk of extinction. And when these creatures are in trouble, it messes up the whole ecosystem.
Now not all whales are the same. Scientists have discovered that there was a major split between two main whale groups somewhere down their family tree: the baleen and toothed whales. The baleen whales, like the colossal blue whale, started mass filter-feeding, and their skull changes kind of stalled. On the other hand, toothed whales like dolphins and sperm whales started relying more and more on echolocation. This special feature allowed them to explore all sorts of aquatic niches.
Speaking of echolocation, it's believed that it was the driving force behind the third phase of evolution. Tooth whales, especially sperm whales, started having some really interesting changes in their heads that were linked to their more sophisticated echolocation. Their skulls even became highly asymmetrical to make room for the echolocation organ known as the melon. Sperm whales took this asymmetry to the extreme.
Other experts believe this whale transition from land to water wasn't a natural phenomenon. They believe it was linked to the same asteroid that wiped out the dinosaurs 66 million years ago. But you see, that asteroid didn't just reshape the land; it had a massive impact on the marine world too. It led to the extinction of the large marine reptiles, leaving lots of empty ocean space
. That's when our early whale ancestors started exploring the oceans.
They might not be related to us like sharks are, but we do have something in common with whales too. Just like how our fingerprints are one of a kind, each whale has its own unique tail. That's how scientists tell them apart. Those cut lines and brownish spots are all special traits that develop over time and can't be copied by any other whale. These features help researchers follow where each whale goes and learn about its habits. It's not the only solution to tell whales apart; there's another way by looking at their flippers, which also have some unique features of their own. But these are a bit harder to spot in the water.