Pseudoextinction

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In a single lineage, when an old chronospecies (A) is judged to have changed into a new species (B) by anagenesis, the old species is deemed phyletically extinct. Chronospecies.svg
In a single lineage, when an old chronospecies (A) is judged to have changed into a new species (B) by anagenesis, the old species is deemed phyletically extinct.

Pseudoextinction (or phyletic extinction) of a species occurs when all members of the species are extinct, but members of a daughter species remain alive. The term pseudoextinction refers to the evolution of a species into a new form, with the resultant disappearance of the ancestral form. Pseudoextinction results in the relationship between ancestor and descendant still existing even though the ancestor species no longer exists. [1]

Contents

The classic example is that of the non-avian dinosaurs. [2] While the non-avian dinosaurs of the Mesozoic died out, their descendants, birds, live on today. Many other families of bird-like dinosaurs also died out as the heirs of the dinosaurs continued to evolve, but because birds continue to thrive in the world today their ancestors are only pseudoextinct. [3]

Overview

From a taxonomic perspective, pseudoextinction is "within an evolutionary lineage, the disappearance of one taxon caused by the appearance of the next." [4] The pseudoextinction of a species can be arbitrary, simply resulting from a change in the naming of a species as it evolves from its ancestral form to its descendant form. [5] Taxonomic pseudoextinction has to do with the disappearance of taxa that are categorized together by taxonomists. As they are just grouped together, their extinction is not reflected through lineage; therefore, unlike evolutionary pseudoextinction, taxonomic pseudoextinction does not alter the evolution of daughter species. [6] From an evolutionary perspective, pseudoextinction entails the loss of a species as a result of the creation of a new one. As the primordial species evolves into its daughter species, either by anagenesis or cladogenesis, the ancestral species can be subject to extinction. Throughout the process of evolution, a taxon can disappear; in this case, pseudoextinction is considered an evolutionary event. [6]

From a genetic perspective, pseudoextinction is the "disappearance of a taxon by virtue of its being evolved by anagenesis into another taxon." [7] As all species must have an ancestor of a previous species, much of evolution is believed to occur through pseudoextinction. However, it is difficult to prove that any particular fossil species is pseudoextinct unless genetic information has been preserved. For example, it is sometimes claimed that the extinct Hyracotherium (an ancient horse-like animal commonly known as an eohippus) is pseudoextinct, rather than extinct, because several species of horse, including the zebra and the donkey, are extant today. However, it is not known, and probably cannot be known, whether modern horses actually descend from members of the genus Hyracotherium, or whether they simply share a common ancestor. [8]

One proposed mechanism of pseudoextinction is endocrine disruption (changing hormone levels). Additionally, when the primary sex-ratio (male to female ratio of a population) is male-biased, predicted levels of pseudoextinction increase. [9] Because the variance of the population size increases with time, the probability of pseudoextinction increases with the length of the time horizon used. [10]

Mammal systematist and paleobiologist David Archibald has estimated that as many as 25% of the extinctions recorded in three different early Puercan mammal lineages are pseudoextinctions. [11] Pseudotermination is an extreme form of pseudoextinction, when a lineage continues as a new species; phylogeny is often difficult to determine in such cases. [12]

Extirpation or regional disappearance can be a stage in pseudoextinction when progressive diachronous range contraction leads to final extinction by the elimination of the last refuge or population growth from this temporal bottleneck. [12]

The notion of pseudoextinction is sometimes applied to wider taxa than species. For instance, the entire superorder Dinosauria, as traditionally conceived, would have to be considered as pseudoextinct, because feathered dinosaurs are considered by the majority of modern palaeontologists as the ancestors of modern-day birds. Pseudoextinction for such higher taxa appears to be easier to prove. However, pseudoextinct higher taxa are paraphyletic groups, which are rejected as formal taxa in phylogenetic nomenclature; either all dinosaurs are stem-group birds, or birds are derived dinosaurs, but there is no taxon Dinosauria, acceptable in cladistic taxonomy, that excludes the taxon Aves. Pseudoextinction cannot be applied to the genus or family levels as, “when a species evolves to a new form, causing the pseudoextinction of the ancestral form, the new species is normally assigned the same higher taxa as the ancestor.” When a family or genus goes extinct it must be true extinction, because pseudoextinction would mean that at least one member of the family or genus is still extant. [13]

Pseudoextinction is an event that occurs much more frequently under the assumption of a Phyletic gradualism model of evolution, under which speciation is slow, uniform and gradual. [14] The majority of speciation would occur through anagenesis under this model, resulting in a majority of species undergoing Pseudoextinction. However, the model of punctuated equilibrium is more widely accepted, with the proposal that most species remain in stasis, a state of very little evolutionary change, for a large proportion of the species' lifespan. [15] This would result in increased cases of speciation through cladogenesis and true extinction, with fewer cases of Pseudoextinction. Nearly all species undergo true extinction under the model of punctuated equilibrium. [15] Charles Darwin proposed the idea of stasis in his book, On the Origin of Species . He suggested that species spend the majority of their evolutionary lifespan in the same form, having undergone very little morphological or genetic change. [16]

Another concept of species on the tree of life is the composite species concept. It sees one species as occupying all internodes of the tree that have the same combination of (morphological, ecological, etc.) characters. Here, a species starts with the acquisition of a character and ends when another change is fixed in its lineage. This process - of one lineage turning into what is afterwards seen as another species because of the fixation of a novel character - is often called anagenesis. In this situation, a species is considered to end by definition but is not really extinct (it survived, after all, in the form of one descendent species with a different character combination), and so it could also be considered to be a pseudoextinction. On the other hand, under the composite species concept [17] a species continues through a lineage split if only one of the two resulting lineages acquires a new character, an event that is sometimes called speciation through "budding". The one that has a new character is now a new species but the other lineage, the one that looks identical to the common ancestor, is considered to be the common ancestor. An example would be a widespread breeding group remaining unchanged while "budding off" a small isolated population that accumulates changes until it cannot interbreed with the others any more. [18]

See also

Related Research Articles

Gradualism, from the Latin gradus ("step"), is a hypothesis, a theory or a tenet assuming that change comes about gradually or that variation is gradual in nature and happens over time as opposed to in large steps. Uniformitarianism, incrementalism, and reformism are similar concepts.

Macroevolution Evolution on a scale at or above the level of species

Macroevolution in the modern sense is evolution that is guided by selection among interspecific variation, as opposed to selection among intraspecific variation in microevolution. This modern definition differs from the original concept, which referred macroevolution to the evolution of taxa above the species level.

Paraphyly Type of taxonomic group

In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic with respect to the excluded subgroups. In contrast, a monophyletic group includes a common ancestor and all of its descendants. The terms are commonly used in phylogenetics and in the tree model of historical linguistics. Paraphyletic groups are identified by a combination of synapomorphies and symplesiomorphies. If many subgroups are missing from the named group, it is said to be polyparaphyletic.

Punctuated equilibrium Theory in evolutionary biology

In evolutionary biology, punctuated equilibrium is a theory that proposes that once a species appears in the fossil record, the population will become stable, showing little evolutionary change for most of its geological history. This state of little or no morphological change is called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.

Speciation Evolutionary process by which populations evolve to become distinct species

Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages. Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book On the Origin of Species. He also identified sexual selection as a likely mechanism, but found it problematic.

Archosaur Group of diapsids broadly classified as reptiles

Archosauria is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of term which includes birds. Extinct archosaurs include non-avian dinosaurs, pterosaurs, and extinct relatives of crocodilians. Modern paleontologists define Archosauria as a crown group that includes the most recent common ancestor of living birds and crocodilians, and all of its descendants. The base of Archosauria splits into two clades: Pseudosuchia, which includes crocodilians and their extinct relatives, and Avemetatarsalia, which includes birds and their extinct relatives.

Cladogenesis Evolutionary splitting of a parent species into two distinct species, forming a clade

Cladogenesis is an evolutionary splitting of a parent species into two distinct species, forming a clade.

Index of evolutionary biology articles

This is a list of topics in evolutionary biology.

Evolutionary taxonomy, evolutionary systematics or Darwinian classification is a branch of biological classification that seeks to classify organisms using a combination of phylogenetic relationship, progenitor-descendant relationship, and degree of evolutionary change. This type of taxonomy may consider whole taxa rather than single species, so that groups of species can be inferred as giving rise to new groups. The concept found its most well-known form in the modern evolutionary synthesis of the early 1940s.

Anagenesis is the gradual evolution of a species that continues to exist as an interbreeding population. This contrasts with cladogenesis, which occurs when there is branching or splitting, leading to two or more lineages and resulting in separate species. Anagenesis does not always lead to the formation of a new species from an ancestral species. When speciation does occur as different lineages branch off and cease to interbreed, a core group may continue to be defined as the original species. The evolution of this group, without extinction or species selection, is anagenesis.

Parallel evolution is the similar development of a trait in distinct species that are not closely related, but share a similar original trait in response to similar evolutionary pressure.

Neontology is a part of biology that, in contrast to paleontology, deals with living organisms. It is the study of extant taxa : taxa with members still alive, as opposed to (all) being extinct. For example:

In phylogenetics, a sister group or sister taxon comprises the closest relative(s) of another given unit in an evolutionary tree.

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. In this view no clear line of demarcation exists between an ancestral species and a descendant species, unless splitting occurs. The theory is contrasted with punctuated equilibrium.

Evolutionary grade Non-monophyletic grouping of organisms united by morphological or physiological characteristics

A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.

Punctuated gradualism

Punctuated gradualism is a microevolutionary hypothesis that refers to a species that has "relative stasis over a considerable part of its total duration [and] underwent periodic, relatively rapid, morphologic change that did not lead to lineage branching". It is one of the three common models of evolution.

Ghost lineage Phylogenetic lineage that is inferred to exist but has no fossil record

A ghost lineage is a hypothesized ancestor in a species lineage that has left no fossil evidence yet can be inferred to exist because of gaps in the fossil record or genomic evidence. The process of determining a ghost lineage relies on fossilized evidence before and after the hypothetical existence of the lineage and extrapolating relationships between organisms based on phylogenetic analysis. Ghost lineages assume unseen diversity in the fossil record and serve as predictions for what the fossil record could eventually yield; these hypotheses can be tested by unearthing new fossils or running phylogenetic analyses.

Evolution of reptiles Origin and diversification of reptiles through geologic time

Reptiles arose about 310 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds and mammals that are descended from early traditionally-defined reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.

Outline of evolution Hierarchical outline list of articles related to evolution

The following outline is provided as an overview of and topical guide to evolution:

This glossary of evolutionary biology is a list of definitions of terms and concepts used in the study of evolutionary biology, population biology, speciation, and phylogenetics, as well as sub-disciplines and related fields. For additional terms from related glossaries, see Glossary of genetics, Glossary of ecology, and Glossary of biology.

References

  1. ↑ Leighton, Lindsey R. (2009). "Taxon Characteristics That Promote Survivorship Through the Permian-triassic Interval: Transition from the Paleozoic to the Mesozoic Brachiopod Fauna". Paleobiology. 34: 65–79. doi:10.1666/06082.1. S2CID   86843206.
  2. ↑ Newman, Mark (2003). Modeling Extinction. p. 102. ISBN   9780195159462.
  3. ↑ Newman, Mark; Palmer, R. J. (2003). Modeling Extinction. Oxford University Press. p. 18. ISBN   978-0195159462.
  4. ↑ Allaby, Michael (2014). A Dictionary of Zoology (4th ed.). Oxford University Press. ISBN   978019968427-4.
  5. ↑ Webb, S.D. (1969). "Extinction-origination equilibria in late Cenozoic land mammals of North America". Evolution. 23 (4): 688–702. doi:10.2307/2406863. JSTOR   2406863. PMID   28562877.
  6. 1 2 Archibald, David J. (1993). "The Importance of Phylogenetic Analysis for the Assessment of Species Turnover: A Case History of Paleocene Mammals in North America". Paleobiology. 19: 1–27. doi:10.1017/S0094837300012288. S2CID   86151240.
  7. ↑ King, Michael; Mulligan, Pamela; Stansfield, William (2014). A Dictionary of Genetics (8th ed.). Oxford University Press.
  8. ↑ Minkoff, Eli; Baker, Pamela (2003). Biology Today: An Issues Approach. Garland Science. p. 648.
  9. ↑ Hanson, Niklas; Aberg, Per; Sundelof, Andreas (May 2005). "Population Level Effects Male Biased Broods in Eelpout(Zoarces Viviparus)". Environmental Toxicology and Chemistry. 24 (5): 1235–1241. doi:10.1897/04-185r.1. PMID   16111005. S2CID   8100503.
  10. ↑ Hanson, Niklas (May 2005). "Environmental Toxicology and Chemistry". ProQuest   210374800.{{cite journal}}: Cite journal requires |journal= (help)
  11. ↑ Keller, Gerta; Kerr, Andrew (2014). Volcanism, Impacts, and Mass Extinction: Causes and Effects. Boulder, Colorado: The Geological Society of America, Inc. p. 17. ISBN   978-0-8137-2505-5.
  12. 1 2 Westermann, Gerd E.G. (2001). "Modes of extinction, pseudo-extinction and distribution in Middle Jurassic ammonites: terminology". Canadian Journal of Earth Sciences. 38 (2): 187–195. Bibcode:2001CaJES..38..187W. doi:10.1139/cjes-38-2-187.
  13. ↑ "Birds: The Late Evolution of Dinosaurs". Natural History Museum. Retrieved October 28, 2015.
  14. ↑ Eldredge, N (1972). Punctuated equilibria: an alternative to phyletic gradualism. San Francisco: Freeman Cooper. p. 84.
  15. 1 2 Gould, S. J. (2002). The Structure of Evolutionary Theory. p. 606.
  16. ↑ Darwin, Charles (1869). On the Origin of Species. London: John Murray. p. 551.
  17. ↑ Kornet, D. J. (2005). The Composite Species Concept: A Rigorous Basis for Cladistic Practice. Netherlands. pp. 95–123.
  18. ↑ Zander, Richard (2013). A Framework for Post-Phylogenetic Systematics. ISBN   978-1492220404.
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