North Pacific right whales are large baleen whales with many distinguishing physical characteristics. They have a stocky black body, white on the underside, no dorsal fin, their head is around 1/4 of the overall body length, the lower lips is strongly bowed, and large callosities (raised patches of rough skin) on their head. They have two rows of baleen plates that hang from the upper jaw and their tail, or fluke, is broad, up to 20 feet (6 m) wide and has a deep notch. North Pacific right whales are the rarest of the large whale species and one of the rarest of all marine mammal species.