Fin whales have deep grey to dark brown/black upper bodies and sides, while their underbellies and beneath their flippers and flukes are creamy white. Stretching from the lower jaw to the navel are 50-100 grooves that expand when the whales take in water during feeding -- characteristic of baleen whales. They also have a prominent, 60 cm dorsal fin located three-quarters of the way along their back which is slightly curved. A unique feature of the fin whale is the colouring pattern around the jaw area: their lower jaw is grey or black on the left side while white on its right side. This asymmetry is helpful to use when identifying and distinguishing fin whales from other whale species; however, no firm agreement exists as to the purpose of the asymmetrical colour pattern. It is suggested that it may be related to the fact that they primarily surface feed on their right sides.