Chronospecies
Encyclopedia
A chronospecies describes a group of one or more species
derived from a sequential development pattern
which involves continual and uniform changes from an extinct ancestral form on an evolutionary scale. This sequence of alterations eventually produces a population which is physically, morphologically
, and/or genetically
distinct from the original ancestors. Throughout this change, there is only one species in the lineage at any point in time, as opposed to cases where divergent evolution
produces contemporary species with a common ancestor.
The related term paleospecies (or palaeospecies) indicates an extinct species only identified with fossil
material. This 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 which exists in the later species.
A paleosubspecies (or palaeosubspecies) identifies an extinct subspecies
which evolved into the currently existing form. This 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 adapting 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 which 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 (e.g. always smaller but with the same proportions) as a living species might represent the final step in a chronospecies. This possible identification of the immediate ancestor of the living taxon
may also rely on stratigraphic information to establish the age of the specimens.
The concept of chronospecies is related to the phyletic gradualism
model of evolution, and 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.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
derived from a sequential development pattern
Anagenesis
Anagenesis, also known as "phyletic change," is the evolution of species involving an entire population rather than a branching event, as in cladogenesis. When enough mutations have occurred and become stable in a population so that it is significantly differentiated from an ancestral population,...
which involves continual and uniform changes from an extinct ancestral form on an evolutionary scale. This sequence of alterations eventually produces a population which is physically, morphologically
Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...
, and/or genetically
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
distinct from the original ancestors. Throughout this change, there is only one species in the lineage at any point in time, as opposed to cases where divergent evolution
Divergent evolution
Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation...
produces contemporary species with a common ancestor.
The related term paleospecies (or palaeospecies) indicates an extinct species only identified with fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
material. This 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 which exists in the later species.
A paleosubspecies (or palaeosubspecies) identifies an extinct subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
which evolved into the currently existing form. This connection with relatively recent variations, usually from the Late Pleistocene
Late Pleistocene
The Late Pleistocene is a stage of the Pleistocene Epoch. The beginning of the stage is defined by the base of the Eemian interglacial phase before the final glacial episode of the Pleistocene 126,000 ± 5,000 years ago. The end of the stage is defined exactly at 10,000 Carbon-14 years BP...
, often relies on the additional information available in subfossil
Subfossil
Subfossil refers to remains whose fossilization process is not complete, either for lack of time or because the conditions in which they were buried were not optimal for fossilization....
material. Most of the current species have changed in size adapting to the climatic changes during the last ice age (see Bergmann's Rule
Bergmann's Rule
Bergmann's rule is an ecogeographic principle that states that within a broadly distributed genus, species of larger size are found in colder environments, and species of smaller size are found in warmer regions. Although originally formulated in terms of species within a genus, it has often been...
).
The further identification of fossil specimens as part of a "chronospecies" relies on additional similarities which 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 (e.g. always smaller but with the same proportions) as a living species might represent the final step in a chronospecies. This possible identification of the immediate ancestor of the living taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
may also rely on stratigraphic information to establish the age of the specimens.
The concept of chronospecies is related to the phyletic gradualism
Phyletic gradualism
Phyletic gradualism is a model of evolution which theorizes that most speciation is slow, uniform and gradual. When evolution occurs in this mode, it is usually by the steady transformation of a whole species into a new one...
model of evolution, and 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
- Coragyps (chronospecies)
- Gymnogyps (palaeosubspecies)
- PantheraPantheraPanthera is a genus of the family Felidae , which contains four well-known living species: the tiger, the lion, the jaguar, and the leopard. The genus comprises about half of the Pantherinae subfamily, the big cats...
(numerous chrono- and paleospecies and -subspecies) - Valdiviathyris (no visible change since the PriabonianPriabonianThe 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 and...
, 35 million years ago)
Further reading
- Evolutionary species vs. chronospecies from Dr. Steven M. Carr, Memorial University of Newfoundland biology department
- Stanley, S. M. (1978) "Chronospecies' longevities, the origin of genera, and the punctuational model of evolution," Paleobiology, 4, 26-40.