In the mammalian race to food snobbery, whales are at the back of the pack. They don't even know what umami is. They're likely rather adept, however, at determining the salt content of a given food item. Salt, after all, is the only thing whales can taste. According to a new study, evolutionary gene mutations among cetacean ancestors -- which include whales and dolphins -- have rendered four of five taste bud types useless, destroying their ability to taste sweet, bitter, umami (savory) and sour. Almost all other vertebrates have the full array of functioning taste sensors. Researchers made their discovery while sequencing the genomes of 15 species, including baleen whales, like bowheads and minkes, as well toothed species, like bottlenose dolphins and sperm whales. "The loss of bitter taste is a complete surprise, because natural toxins typically taste bitter," explained zoologist Huabin Zhao of Wuhan University in China, the study's lead researcher. The study was published earlier this month in journal Genome Biology and Evolution. The fact that most whale species swallow their food whole may at least partially explain the loss of taste buds, as flavors are mostly released when food is chewed. Mutations often infiltrate the genetic code after certain traits become useless. But the retention of salty taste receptors, scientists say, may help whales maintain proper sodium levels and blood pressure. Still, if the price of a strengthened sense of salt is the the inability to taste dangerous substances, it's a cost that sometimes proves perilous. Packs of killer whales have unknowingly swum into the middle of oil spills, and dolphins have died after eating fish filled with algal toxins.