Much of biologist Hannah Stowe's memoir, Move Like Water, records her experiences on sailing vessels researching cetaceans – an entirely aquatic group of mammals that includes whales, dolphins and porpoises.  Some interesting trivia regarding these magnificent creatures:
 

1. The fossil record shows the first cetaceans evolved from land-dwelling quadrupeds around 55.8 to 49 million years ago, in the Early Eocene epoch. Their ancestors were deer-like creatures that moved back into the sea, flippers replacing their legs over the eons.
2. At up to 32 feet long, the orca (aka killer whale) is the largest member of the oceanic dolphin family. The common bottlenose dolphin, which defines the family for many people, ranges from 8 to 13 feet, and the smallest is the Hector's dolphin, at only 4 feet in length.
3. The blue whale is the largest creature ever to have lived on Earth. It can reach up to 100 feet long and weigh 200 tons – as much as 33 elephants. Its heart alone ...