Fastest animals
The fastest land animal is the cheetah, which has a recorded speed of . The peregrine falcon is the fastest bird and the fastest member of the animal kingdom with a diving speed of . The fastest animal in the sea is the black marlin, which has a recorded speed of .
Dolphin
Dolphins have two pectoral flippers, containing four digits, a boneless dorsal fin for stability, and a tail fin for propulsion. Although dolphins do not possess external hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. Dolphins are fast swimmers in comparison to seals which typically cruise at ; the killer whale (orca), in comparison, can travel at speeds up to . The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, which means they are unable to turn their heads. River dolphins, however, have non-fused neck vertebrae and are able to turn their head up to 90°. Dolphins swim by moving their tail fin and rear body vertically, while their flippers are mainly used for steering. Some species log out of the water, which may allow them to travel faster. Their skeletal anatomy allows them to be fast swimmers. All species have a dorsal fin to prevent themselves from involuntarily spinning in the water.