Whales have not always inhabited the Arctic. The earliest whales, which evolved between 50 and 55 million years ago, came from temperate or mild regions. Modern whales that we recognize today appeared between 20 and 25 million years ago. Today there are three whale species that inhabit the Arctic: bowhead whales (a baleen whale), belugas, and narwhals (toothed whales in the family Monodontidae).
Fossils of beluga and narwhal ancestors from six to 10 million years ago have been found as far south as Baja California, Mexico. These early monodontids shifted their distribution northward around 4.7 million years ago. Fossils of whales closely related to bowheads from around that time have been found in Virginia and North Carolina.
About 2.5 million years ago, ice sheets started forming in the Arctic. These ice sheets have since advanced and retreated every 40,000-100,000 years in intervals called glacial periods. The earliest bowhead whale fossils found in the Arctic date back 30,000-40,000 years, which may indicate that modern bowhead whales evolved in connection with the ice. Similarly around 10,000-20,000 years ago modern belugas were common in the Arctic.
All three species have adapted to conditions in the Arctic. Thick blubber insulates them from the cold and acts as a reserve of energy to help them through relatively lean winters. They also lack the dorsal fins found on most other species of whales, but have a ridge along their backs or a highly placed blowhole. These adaptations probably make it easier for them to breathe in heavy ice cover. Finally, belugas have a special adaptation of extra vertebrae in their necks, allowing them to turn their heads to breathe through smaller holes in the ice.
— Elizabeth Henderson, postdoctoral researcher, Whale Acoustics Laboratory