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 .
Convergent evolution
Swimming animals including fish such as herrings, marine mammals such as dolphins, and ichthyosaurs (of the Mesozoic) all converged on the same streamlined shape. The fusiform bodyshape (a tube tapered at both ends) adopted by many aquatic animals is an adaptation to enable them to travel at high speed in a high drag environment. Similar body shapes are found in the earless seals and the eared seals: they still have four legs, but these are strongly modified for swimming.