What is an evolutionary tree? Is there a precise evolutionary tree known by science that explains the emergence and origin of every type of living being?

Evolutionary tree is the pictorial and schematic showing of evolutionary relations among species of living beings in which the trunk (or a preceding branch) shows common ascendants of species and groups of living beings that are distributed along its branches according to hypothesis on their origin. For instance, today it is admitted that birds and mammals are two distinct branches of the similar preceding reptile branch.

Biology cannot assure a exact evolutionary tree (phylogeny) on the species of living beings that live or have lived in our planet. There are many data to be discovered and many knowledge gaps to be filled. One of the most promising methods to study phylogeny is the comparison of DNA molecules from different groups of living beings researching similarity and dissimilarity in nucleotide sequences that may show more or less relatedness among species.