Earth's humpback whales, extinct by the 23rd century, whose song an alien probe came to hear and which Kirk's crew brought forward from 1986 to save the planet.
Humpback whales are at the centre of Star Trek IV: The Voyage Home. In 2286 a powerful probe arrives at Earth, sending signals that vaporise the oceans and cripple power systems. Spock realises that it is calling to humpbacks, which were hunted to extinction in the 21st century.
Kirk takes his captured Klingon Bird-of-Prey back to 1986 San Francisco, where the biologist Gillian Taylor cares for two humpbacks, George and Gracie, at the Cetacean Institute. Scotty trades the formula for transparent aluminium to build a tank, and the crew beam the whales aboard just ahead of a whaling ship.
Released into San Francisco Bay in the future, the whales answer the probe and it departs. Gracie is pregnant, giving the species a new start.