Pliny suggested that the ostrich, then newly discovered, was the result of a cross between a giraffe and a gnat. (It would, I suppose, have to be a female giraffe and a male gnat.) In practice there must be many such crosses which have not beenattempted because of a certain understandable lack of motivation.
Carl Sagan, Dragons of Eden: Speculations on the Evolution of Human Intelligence
animal-evolution, evolution, species