Dolphins

Dolphins — comprising approximately 40 species of oceanic dolphins and 7 river dolphins — are among the most intelligent non-human animals. They use signature whistles as names (each dolphin has a unique call that others use to address it); they demonstrate cultural transmission (behaviors spreading through populations, not genetics); they cooperate with human fishermen in Brazil's Laguna, signaling when fish are near and when to cast nets. Dolphins use echolocation (like bats but far more sophisticated) to navigate and hunt — they can detect objects behind barriers, discriminate between materials by density, and form mental images from sound. They have spindle neurons associated with empathy and self-recognition; they comfort grieving companions. Common dolphins were observed protecting a humpback whale from killer whales — apparent interspecies altruism.