Living fossil

The coelacanths were thought to have gone extinct 66 million years ago, until a living specimen belonging to the order was discovered in 1938.

A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living fossils commonly are of species-poor lineages, but they need not be. While the body plan of a living fossil remains superficially similar, it is never the same species as the remote relatives it resembles, because genetic drift would inevitably change its chromosomal structure.

Living fossils exhibit stasis (also called "bradytely") over geologically long time scales. Popular literature may wrongly claim that a "living fossil" has undergone no significant evolution since fossil times, with practically no molecular evolution or morphological changes. Scientific investigations have repeatedly discredited such claims.[1][2][3]

The minimal superficial changes to living fossils are mistakenly declared as an absence of evolution, but they are examples of stabilizing selection, which is an evolutionary process—and perhaps the dominant process of morphological evolution.[4]

  1. ^ Casane, Didier; Laurenti, Patrick (2013-04-01). "Why coelacanths are not 'living fossils'". BioEssays. 35 (4): 332–338. doi:10.1002/bies.201200145. ISSN 1521-1878. PMID 23382020. S2CID 2751255.
  2. ^ Mathers, Thomas C.; Hammond, Robert L.; Jenner, Ronald A.; Hänfling, Bernd; Gómez, Africa (2013). "Multiple global radiations in tadpole shrimps challenge the concept of 'living fossils'". PeerJ. 1: e62. doi:10.7717/peerj.62. PMC 3628881. PMID 23638400.
  3. ^ Grandcolas, Philippe; Nattier, Romain; Trewick, Steve (2014-01-12). "Relict species: a relict concept?". Trends in Ecology & Evolution. 29 (12): 655–663. doi:10.1016/j.tree.2014.10.002. ISSN 0169-5347. PMID 25454211.
  4. ^ Lynch, M (1990). "The rate of evolution in mammals from the standpoint of the neutral expectation". The American Naturalist. 136 (6): 727–741. doi:10.1086/285128. S2CID 11055926.

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