What animals are dolphins closely related to?

Whales.

Six species in the family Delphinidae are commonly called "whales", but genetically are dolphins. They are sometimes called blackfish.

• Melon-headed Whale, Peponocephala electra
• Killer Whale (Orca), Orcinus orca
• Pygmy Killer Whale, Feresa attenuata

  Wolphin Kawili'Kai at the Sea Life Park in Hawaii.

• False Killer Whale, Pseudorca crassidens
• Long-finned Pilot Whale, Globicephala melas
• Short-finned Pilot Whale, Globicephala macrorhynchus