The process of evolution produces a pattern of relationships between species. As lineages evolve and split and modifications are inherited, their evolutionary paths diverge.
There is a hypothesis about the relationships among organisms. It is shown in a tree called a phylogeny. It illustrates the idea that all of life is related and can be divided into three major domains: Archaea, Bacteria, and Eukaryota.
The tree is supported by many lines of evidence, but it is probably not flawless. Scientists constantly reevaluate hypotheses and compare them to new evidence. For example, evidence discovered in the last 50 years suggests that birds are dinosaurs, which required adjustment to several "vertebrate twigs."
Phylogenies trace patterns of shared ancestry between lineages. Here are some examples:
http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_05
http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_06
Next: The History of Life and How Does Evolution Work
Which phylogeny do you ascribe to? They are different if you base it on physiology or dna structure