About 50 species of birds on Earth today do not belong to the same group as the other 10,000 currently in existence. Known as the paleognaths, this small group features many of the largest and heaviest bird specimens on our planet, bringing together ostriches and their distant South American relatives the rheas, as well as emus and cassowaries. Ground-dwelling kiwis and tinamous complete the family. None of these birds can fly, except for the tinamous....