A timetree is a

phylogenetic tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In ...

scaled to time. It shows the

evolutionary Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certa ...

relationships of a group of organisms in a temporal framework.Hedges SB; Kumar S (2009).
Discovering the timetree of life
'' in ''The Timetree of Life,'' SB Hedges and S Kumar, Eds. (New York: Oxford University Press, 2009) P. 3-18 Therefore, if living organisms are represented, the branch length between the base of the tree and all leafs (e.g., species) is identical because the same time has elapsed, although extinct organisms can be shown in a timetree. As with a phylogenetic tree, timetrees can be drawn in different shapes: rectangular, circular, or even spiral. The only figure in Darwin's ''

On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life'')The book's full original title was ''On the Origin of Species by M ...

'', one of the earliest printed evolutionary trees, is a hypothetical timetree. Because the

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

has always been tightly linked to the

geologic record The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata. That is, deposits laid down by volcanism or by deposition of sediment derived from weathering detritus (clays, sa ...

, evolutionary trees of extinct organisms are typically illustrated as timetrees.

History

In the past, timetrees were sometimes called " chronograms," but that term has been criticized because it is imprecise, referring to any graph that shows time, and not indicating that evolutionary relationships are involved. The first use of the single word "timetree," in the context of an evolutionary tree scaled to time, was in 2001.Hedges SB (2001)
Molecular evidence for the early history of living vertebrates
Pp. 119-134 in P. E. Ahlberg (Ed.) ''Major events in early vertebrate evolution: palaeontology, phylogeny, genetics and development.'' London: Taylor and Francis.

References

{{reflist Evolutionary biology Phylogenetics Diagrams