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 appropriate s ...

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 Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar working i ...

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 that evolved into the currently-existing form. The connection with relatively-recent variations, usually from the Late Pleistocene, often relies on the additional information available in subfossil material. Most of the current species have changed in size and so

adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...

to the climatic changes during the last ice age (''see'' Bergmann's Rule). 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 Phyletic gradualism is a model of evolution which theorizes that most speciation is slow, uniform and gradual.Eldredge, N. and S. J. Gould (1972)"Punctuated equilibria: an alternative to phyletic gradualism"In T.J.M. Schopf, ed., ''Models in Pa ...

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'' (several paleospecies and -subspecies) * Marine sloths (paleospecies) * ''

Coragyps ''Coragyps'' is a genus of New World vulture that contains the black vulture ''(Coragyps atratus)'' and two extinct relatives. One extinct species is the 'western' black vulture, ''Coragyps occidentalis'', a larger ancestral relative of the mod ...

'' (chronospecies) * ''

Gymnogyps ''Gymnogyps'' is a genus of New World vultures in the family Cathartidae. There are five known species in the genus, with only one being extant, the California condor. Fossil species *''Gymnogyps amplus'' was first described by L. H. Miller in ...

'' (paleospecies) * '' Panthera'' (numerous chrono- and paleospecies and -subspecies) * ''

Valdiviathyris ''Valdiviathyris'' is a genus of craniate brachiopods that has changed little since the Silurian, from when fossils are known. The extant species ''V. quenstedti'' is known from the late Eocene. It was initially known only from the holotype coll ...

'' (no visible change since the Priabonian, 35 million years ago)

References

External links

{{Wiktionary Evolutionary biology Biostratigraphy Phylogenetics

Examples

See also

References

Further reading

External links