The importance of fossils in deciding evolutionary relationships is that they provide evidence that the present animals (and plants) have originated from the previously existing animals (and plants) through the process of continuous evoltion. For example, a fossil bird called Archaeoptinryx looks like a bird but it has many other features which are found in reptiles. This is because Archaeopteryx has feathered wings like those of and birds, but teeth and tail like those of reptiles. Archaeopteryx is , therefore a connenting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles.
