Pygmy killer whale

The Pygmy Killer Whale (Feresa attenuata) is a small, rarely-seen cetacean of the oceanic dolphin family (Delphinidae). It derives its common name from the fact that it shares some physical characteristics with the orca ("killer whale"). In fact, "killer" may be a more apt name in the case of the Pygmy Killer Whale than its larger genetic cousin. When a number of Pygmy Killers were brought into captivity in Hawaii and South Africa they were extremely aggressive—even killing one another. A third herd captured in Japan did not display such aggression.
Until the early 1950s the Pygmy Killer Whale was only known from two skulls kept at the British Museum. The first description was recorded by John Gray in 1874. In 1954 Japanese cetologist Muneasto Yamada published accounts of a "rare porpoise" discovered by whale hunters working from Honshū in 1952. He wrote that the individuals he examined had skulls matching those in the Museum but that also the body had similar features to the Killer Whale, and proposed the common name Lesser (or Pygmy) Killer Whale. Despite its name and features, the pygmy killer whale is not closely related to the orca.
The scientific species descriptor attentuata is Latin for 'tapering' and refers to the gradual narrowing from the head to the tail fin of the dolphin.