Baleen whales have symmetrical skulls. Concentrated masses of prey are preferable for this method of feeding. Gulpers include most rorquals, blue whales, pygmy blue whales, fin whales , Bryde's whales, humpback whales, and minke whales. Skimmers - these whales keep their mouths open most of the time, filtering food all the while. Sei whales do both.
Gray whales are benthic feeders.
Baleen whales evolved about 35 million years ago, during the early Oligocene Epoch. The earliest baleen whale fossils are from New Zealand. They have baleen plates instead of teeth, which they use to filter food. They are larger than the toothed whales and have two blow holes. As it swims along the bottom of the ocean stirring up sediment, it takes the nutrient-rich murky water into its mouth, and forces it out through its short baleen, retaining tiny organisms.