A chronospecies is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

derived from a sequential development pattern that involves continual and uniform changes from an extinct ancestral form on an evolutionary scale. The sequence of alterations eventually produces a population that is physically, morphologically, and/or genetically distinct from the original ancestors. Throughout the change, there is only one species in the lineage at any point in time, as opposed to cases where

divergent evolution Divergent evolution or divergent selection is the accumulation of differences between closely related populations within a species, leading to speciation. Divergent evolution is typically exhibited when two populations become separated by a geog ...

produces contemporary species with a common ancestor. The related term paleospecies (or palaeospecies) indicates an extinct species only identified with

fossil 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 ...

material. That identification relies on distinct similarities between the earlier fossil specimens and some proposed descendant although the exact relationship to the later species is not always defined. In particular, the range of variation within all the early fossil specimens does not exceed the observed range that exists in the later species. A paleosubspecies (or palaeosubspecies) identifies an extinct

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. Not all specie ...

that evolved into the currently-existing form. The connection with relatively-recent variations, usually from the

Late Pleistocene The Late Pleistocene is an unofficial age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a stratigraphic perspective. It is intended to be the fourth division of the Pleistocene Epoch withi ...

, often relies on the additional information available in

subfossil 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 ...

material. Most of the current species have changed in size and so adapted to the climatic changes during the last ice age (''see''

Bergmann's Rule Bergmann's rule is an ecogeographical rule that states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations and species of smaller size are found in warmer r ...

). The further identification of fossil specimens as part of a "chronospecies" relies on additional similarities that more strongly indicate a specific relationship with a known species. For example, relatively recent specimens, hundreds of thousands to a few million years old with consistent variations (such as always smaller but with the same proportions) as a living species might represent the final step in a chronospecies. The possible identification of the immediate ancestor of the living

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

may also rely on

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

information to establish the age of the specimens. The concept of chronospecies is related to the phyletic gradualism model of evolution, and it also relies on an extensive fossil record since morphological changes accumulate over time, and two very different organisms could be connected by a series of intermediaries.

Examples

* ''

Bison Bison are large bovines in the genus ''Bison'' (Greek: "wild ox" (bison)) within the tribe Bovini. Two extant and numerous extinct species are recognised. Of the two surviving species, the American bison, ''B. bison'', found only in North A ...

'' (several paleospecies and -subspecies) * Marine sloths (paleospecies) * '' Coragyps'' (chronospecies) * '' Gymnogyps'' (paleospecies) * ''

Panthera ''Panthera'' is a genus within the family Felidae that was named and described by Lorenz Oken in 1816 who placed all the spotted cats in this group. Reginald Innes Pocock revised the classification of this genus in 1916 as comprising the tig ...

'' (numerous chrono- and paleospecies and -subspecies) * '' Valdiviathyris'' (no visible change since the

Priabonian The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage ...

, 35 million years ago)

References

External links

{{Wiktionary Evolutionary biology Biostratigraphy Phylogenetics

Examples

See also

References

Further reading

External links