Haeckel's famous phylogeny tree is titled "The Pedigree of Man." Its design places different forms of life into ranks with humans as the pinnacle of evolution. The biggest conceptual distinction between this idea of phylogeny and those of modern science is that the idea of rank has been dismissed. Phylogeny trees no longer refer to higher and lower animals. The only axis used now is time.
To account for this change in concept, cladistics researchers have developed a new vocabulary. Instead of "lower" or "primitive," they prefer the term "basal," referring to a branch whose origin is relatively close to the base of a phylogeny tree. Instead of "higher" or "advanced," they use "derived," meaning something that has been derived through evolution from a more basal form.
In a modern phylogeny tree, with time as the only axis, all non-extinct species are placed at the same height. A phylogeny tree that includes extinct, fossilized species often shows those species' branches as ending at the point in geological time when they went extinct. Since rank has been eliminated, a phylogeny tree may be shown in circular rather than linear form to save space.
Phylogeny is an important concept in biology. Taken as a concept from evolution, it is used for classification and for understanding the nature and history of life.