Researchers are starting to get a handle on why ancient creatures returned to the ocean after their ancient ancestors climbed out of it.

Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch. Even though all modern cetaceans are obligate aquatic mammals, early cetaceans were amphibious, and their ancestors were terrestrial…

The deep sea is a part of our planet unlike any other. Accounting for over 95 percent of Earth’s living space, it is cold, dark, and under extreme pressure, yet...