The Killer Whale Imposter
The false killer whale (pdf) (Pseudorca crassidens) is a large dolphin that, despite its name, is not closely related to the killer whale, although they are both in the same family, Delphinidae. Instead, it's named for similarities in their skull shapes, as the first false killer whale was described from a fossil in the mid-1800s. They are very social animals and form strong bonds with each other, causing them to stick together in pods. This can be problematic due to their propensity to get stranded in large groups; as many as 835 have been stranded on dry land at one time. The reasons for this happening are not certain but it is possibly related to human use of sonar underwater.