X, Y, and Z are three animals. The animal X can fly but animal Y can only run on ground or walls. The forelimbs of animals X and Y have the same basic design but they are used for different purposes such as flying and running respectively. The animal Z became extinct a long time ago. The study of fossils of Z tells us that it had some features like those of X and some like those of y. In fact, Z is said to form a connecting link in the evolutionary chain of X and Y.
Which is the correct evolutionary chain involving `X, Y and Z : X to Z to Y or Y to Z to X `?