Most vertebrates enjoy the same five tastes as humans do: sweet, salty, sour, bitter and umami. Dolphins and whales, though, are an exception. According to new research, these animals have lost their ability to perceive any flavors save for salty, ScienceNOW reports.

Scientists analyzed the genomes of 15 different cetacean species, including baleen whales, sperm whales and bottlenose dolphins. Most of the genes responsible for taste sensations, ScienceNOW says, were riddled with mutations and useless for producing the proteins necessary for taste. Only the genes connected to salty flavors remained functional.

These mutations likely occurred around 53 million years ago, after cetaceans' shared ancestors evolved to live in the water, the team told ScienceNOW. The mutations, the scientists think, probably arose because those animals swallow their prey whole and don't need to perceive flavor, which is typically released by chewing.

Usually, taste can clue an animal into whether the food it's eating is nourishing or toxic, ScienceNOW explains. Cetaceans have somehow managed to survive for millions of years without these perceptions. The study authors are concerned, however, that manmade toxins might sneak into the diets of animals which can't perceive them. For example, orcas have swum into oil spills, ScienceNOW reports, and coastal fertilizer runoff in Florida often finds its way into fish that bottlenose dolphins readily gobble up.