Fossils are the remains of organisms formed over a millions of years ago.Evolutionary relationship tells us how closely two organisms are related in evolutionary tree.We ananalyze either the organ structure or the function of an organism and try to compare it with another orgainsm in order to find how closely they are related.The more closely they are related the more likely that they might have had a common ancestor. We can easily examine the structures of organisms that are present now but if we had to trace the evolutionary relationship of organisms that were alive millions of years ago,then we will need fossils.These fossils are an easy way of understanding the ancient species and also it helps us to find the missing link in the evolutionary tree.By knowing more about the organism that lived so many centuries ago,we can understand the changes in the body designs and functions that led to the creation of species in n the due course of evolution and also the evolution itself.We get to understand the prehistoric period and the geographical changes that might have given rise to the organisms by analysing the structure of the organisms in fossils.As we trace the relationship using tgses fossils and go back in time,at one point we might reach a time when organisms evolved from single ancestor and also non material things.Fossils are the key to understand the similarity between organisms and create a hierarchy that would let us to classify the organisms and learn them easily without having learn about all the organisms that ever survived. Nowadays molecular phylogeny is also put in use in order to examine the evolutionary relationship more closely.