Dolphins don't need to see or hear nearby family or friends to know they're around. They can just taste their urine in the water, according to new research published in the journal Science Advances.
From The Guardian:
[Scottish Ocean Institute director Vincent] Janek, the lead author, said: "Dolphins explored urine samples for longer if they came from known animals or when they were presented together with the dolphin's unique and distinctive signature whistle, an acoustic identifier that works like a name."[…]
Janik added: "We still know very little about how the sense of taste works in dolphins. Other studies have shown that they lost a lot of the common tastes that we find in other mammals such as sour, sweet, umami or bitter. But they have unusual sensory cells on their tongue that are probably involved in this detection of individual tastes of other animals."