Phylogeny describes the relationships between groups of animals as understood by ancestor/descendant history, so that groups are linked together on the basis of the recency of common ancestry. This is assessed primarily by the recognition of shared derived characters. The pattern of evolutionary relationships within and between groups can be depicted in the form of a branching diagram called cladograms, which are like genealogies of species.
Not only is phylogeny important for understanding paleontology, but paleontology in turn contributes to phylogeny. Many groups of organisms are now extinct, and without their fossils we would not have as clear a picture of how modern life is interrelated.
Evolutionist Ernst Haeckel is well known for his claim that "ontogeny recapitulates phylogeny," meaning that organisms pass through stages in development that mirror their evolutionary history. Though some of the drawings he produced as evidence of this claim were later found to be fraudulent, evolutionary biologists maintain that other evidence supports this conclusion, albeit not as strongly as Haeckel suspected.