Are Whales Mammals? Yes, and They're Related to Hippos

Whales are warm-blooded, breathe air through lungs, give birth to live young, and nurse them with mammary glands — all defining characteristics of mammals. Like dolphins and sea lions, whales rely on oxygen, not gills, and must surface regularly to breathe. This places them squarely in the group known as marine mammals.

Modern whales evolved from land mammals about 50 million years ago. Fossil evidence shows that terrestrial mammals gradually adapted to aquatic life, giving rise to the ancestors of today's whales, dolphins, and porpoises. The fossil record reveals limb changes, nostril migration, and spine adaptations that transformed land animals into the oceanic giants we know today.

There are two main types of whales: baleen whales and toothed whales.

Baleen whales — like blue whales, humpback whales, right whales and minke whales — use comb-like structures called baleen to filter tiny organisms from seawater. This process is known as filter feeding, and it's essential for these gentle giants to consume enough food.

On the other hand, toothed whales include species like sperm whales, killer whales (orcas), beaked whales and pygmy sperm whales. These animals use teeth to hunt squid, fish and even other marine mammals.

Most toothed whales are smaller than their baleen counterparts, but they're often more social and exhibit complex behaviors.

There are many whale species spread across all the world's oceans. Some, like the bowhead whale and beluga whales, are adapted to life in polar waters, while species like the grey whale and sei whale can be found migrating along the western coast of North America.

Unfortunately, many whale species have suffered due to commercial whaling. Iconic species like the North Atlantic right whale and fin whale are considered endangered because of past overhunting and current environmental threats.

Efforts to protect whales and restore whale populations are ongoing, supported by conservation groups and scientists around the globe.

Whales migrate seasonally, traveling thousands of miles between feeding and breeding grounds. This epic journey helps female whales find safe, warm waters to birth and nurse calves before returning to colder feeding zones.

Male whales may compete for mates through song or displays, particularly among humpback whales known for their haunting underwater melodies. Some larger whales, like the blue whale, can dive into the deep ocean for feeding, while smaller whales and oceanic dolphins stay closer to the surface.

And yes, whales breathe through blowholes, not gills — unlike fish. This means every breath is intentional. They even sleep with part of their brain awake to ensure they make it to the surface.

Believe it or not, whales' closest living relatives are not fish or even other marine mammals. They're actually most closely related to hoofed animals like hippos.

Modern cetaceans — which include whales, bottlenose dolphins and harbor porpoises — share a common ancestor with these land-dwellers.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.