Pseudoextinction
Pseudoextinction (or phyletic extinction) of a species occurs where there are no more living members of that species, but members of a daughter species or subspecies remain alive. 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.
Pseudotermination is extreme form of pseudoextinction, when lineage may continue in form of new species of frequently difficult to predict phylogeny.[1]
Extirpation or regional disappearance is the stage in pseudoextinction, when progressive diachronous range contraction, may lead to, final extinction by the elimination of the last refuge, or population growth from this temporal bottleneck.[1]
Pseudoextinction can sometimes apply to wider taxons than the species level. For instance, the entire Superorder Dinosauria, as traditionally defined, 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 higher appears to be easier to prove. However, pseudoextinct higher taxa are equivalent to paraphyletic groups, which are rejected as unnatural groupings in modern phylogenetic classifications that are based on cladistic reasoning (either all dinosaurs are stem-group birds, or birds are derived dinosaurs, but there is no valid taxon Dinosauria that excludes the taxon Aves). Consequently, the alleged pseudoextinction of higher taxa rather represents an artifact of an obsolete non-phylogenetic classification than a genuine evolutionary phenomenon.
[edit] See also
- Main articles: on Extinction, and the Cretaceous-Tertiary extinction event
- Human extinction
[edit] References
- ^ a b Westermann, Gerd E.G. (2001). "Modes of e×tinction, pseudo-e×tinction and distribution in Middle Jurassic ammonites: terminology". Canadian Journal of Earth Sciences 38: 187. Bibcode 2001CaJES..38..187W. doi:10.1139/cjes-38-2-187.
[edit] External links
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