Living fossil

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Comoros coelacanth (drawing). The coelacanth group has existed for more than 400 million years and has changed little externally in the course of its evolution.

Living fossils are species or groups of species ( taxa ) that have remained more or less unchanged over long geological periods. The term goes back to Charles Darwin , the father of the modern theory of evolution. It is used by different authors with slightly different meanings.

Some modern evolutionary biologists disapprove of the term because, in their opinion, it has a teleological connotation that evolution has a certain direction or speed, which reminds them of obsolete concepts of evolution from the Victorian era . According to these authors, it is impossible to divide taxa into groups like that of the living fossils based on their constancy of characteristics or the speed of evolution, because these are much too variable, so that even from supposedly unchangeable old forms, new species can later emerge in rapid succession. Others continue to use it to this day. The term living fossil is a contradictio in adjecto (a direct contradiction in terms ) because fossils and life are mutually exclusive.

Definitions

The term "living fossil" was introduced into literature by Charles Darwin . In his main work On the Origin of Species (p. 107 in the first edition) he says about freshwater forms such as Ornithorhynchus ( platypus ) and Lepidosiren ( South American lungfish ): “ ..., which, like fossils, connect to a certain extent orders now widely separated in the natural scale. These anomalous forms may almost be called living fossils; they have endured to present day, from having inhabited a confined area, and from having thus been exposed to less severe competition. “(… Which, like fossils, to a certain extent combine different orders that are now widely separated from each other in the natural system. These deviating forms could almost be called living fossils. They have survived to this day because they populated a limited area and were exposed to less fierce competition there. ") The expression is found somewhat earlier in Darwin's correspondence, for example in a letter to Joseph Dalton Hooker in 1858, where he also emphasized that these were relic forms pushed from the sea into freshwater habitats.

Today's authors often cite the same examples when speaking of living fossils, but few give a definition. Thomas Schopf mentions the following in a review from 1984:

  1. A living species that has survived for very long geological periods ( sometimes referred to as "panchronic" ). Is represented by Katsuhiko Yoshida, for example.
  2. A living species that is morphologically and physiologically quite similar to a fossil species that has been separated from it over a long geological period.
  3. A living species that is predominantly characterized by primitive morphological features.
  4. A species according to one of the first three definitions, but which must also have a relic distribution.
  5. A living species that was believed to be extinct ( but today this is more commonly referred to as a Lazarus taxon ).
  6. A living clade of low taxonomic diversity whose species meet one of the first three definitions.

There are a large number of similar definitions, most of which are similar to one of those listed, but differ from one another. Erich Thenius combines these factors: Living fossils would therefore have both an isolated position in the biological system with one or only a few species, a relic spread, compared to earlier widening and also ancient characteristics due to the slow rate of evolution.

Niles Eldredge and Steven M. Stanley, like Thenius and many others, name an "arrested evolution" as an essential characteristic, the forms have therefore not changed significantly morphologically since their emergence and also have a lower evolutionary speed, Schopf does not use this definition considered. A low rate of evolution is described by some authors with the special term "bradytelia" (the term was introduced by the paleontologist George Gaylord Simpson in Tempo and Mode in Evolution 1944).

Depending on the definition used, some authors exclude certain individual taxa from the living fossils that others accept as such. A problem with all attempts at definition is that the underlying terms are inherently vague (how old must a species be in order for it to meet the criterion? How large can a relic area be? Etc.). The "prehistoric crabs" or Notostraca with the genus Triops , for many a prime example of living fossils, obviously have a high rate of speciation recently , despite their blueprint that has been preserved over long periods of time , with numerous species that emerged only recently in different areas. Another of the classic relic groups, the pearl boats ( Nautilidae ), shows evidence of a renewed speciation in a relatively short past. The cycads (Cycadales) are a typical relic group, since radiation in the Jurassic and the Cretaceous only a few species have survived to this day. In fact, the group unexpectedly showed a new radiation in the Miocene, today's species are no older than about 12 million years. The famous bridge lizard or tuatara ( Sphenodon punctatus ) of New Zealand, morphologically almost unchanged since the Cretaceous, unexpectedly has one of the highest molecular evolution speeds of all vertebrates. Unexpectedly high genetic diversity is also shown by another prime example of living fossils, the horseshoe crabs (Limulidae). These examples show that a certain shape showing a characteristic that is considered characteristic of living fossils does not necessarily match the definitions in the other characteristics got to.

In other cases, the morphological stasis is only faked in the fossil record. For a long time , the arm pod Lingula was considered to be possibly the oldest living fossil. In the meantime it has been made plausible that the smooth shell with few features has tempted to mistakenly place numerous, presumably not particularly closely related, forms in a single genus.

In 2013, Didier Casane and Patrick Laurenti used the most famous of all living fossils, the coelacanth Latimeria , to draw attention to the contradictions within the concept. The slow rate of evolution of this species is doubtful, its morphological stasis is based on false assumptions: the coelaceans had a large number of forms in the past, and there are no fossils of Latimeria itself. Thinking in "primitive", "basal", "plesiomorphic" forms is a relapse into the outdated concept of Scala Naturae , so it should be avoided to speak of living fossils at all. This radical approach, however, has been contradicted by other evolutionary biologists. The slow morphological evolution of the coelacanth is actually demonstrable, which has simply been overlooked by their opponents, who are purely fixated on the cladistic characteristics and therefore neglected the temporal dimension. This controversy shows that despite the methodological problems and the difficult delimitation of the concept of living fossils, it still has supporters today. Some authors then tried to solve the problem of the vague definition by quantification and developed what is known as an Evolutionary Performance Index (EPI) to delimit living fossils.

Examples

Plant kingdom

Animal kingdom

supporting documents

  1. ^ Ulrich Lehmann : Paleontological Dictionary . 4th edition. Ferdinand Enke Verlag, Stuttgart 1996, p.  130 .
  2. ^ Letter from C. Darwin to JD Hooker, December 24, 1858. online at Darwin Correspondence Project, University of Cambridge .
  3. ↑ a b Niles Eldrege & Steven M. Stanley (ed.): Living Fossils. Springer Verlag, New York 1984. ISBN 978-1-4613-8273-7 .
  4. ↑ Thomas JM Schopf (1984): Rates of Evolution and the Notion of "Living Fossils". Annual Review of Earth and Planetary Sciences 12: 245-292.
  5. ↑ Katsuhiko Yoshida (2002): Long Survival of "Living Fossils" with Low Taxonomic Diversities in an Evolving Food Web. Paleobiology 28 (4): 464-473.
  6. ↑ Erich Thenius (2003): "Living fossils" in the animal and plant kingdom. Fiction or reality? Writings Association for the Dissemination of Scientific Knowledge 141: 99–123.
  7. ^ TC Mathers, RL Hammond, RA: Jenner, B. Hänfling, A. Gómez (2013): Multiple global radiations in tadpole shrimps challenge the concept of “living fossils”. PeerJ, 1: e62. doi: 10.7717 / peerj.62 .
  8. ^ Charles G. Wray, Neil H. Landman, W. Bruce Saunders, James Bonacum (1995): Genetic divergence and geographic diversification in Nautilus. Palaeobiology 21 (2): 220-228. doi: 10.1017 / S009483730001321X
  9. ↑ NS Nagalingum, CR Marshall, TB Quental, HS Rai, DP Little, S. Mathews (2011): Recent Synchronous Radiation of a living fossil. Science 334: 796-799. doi: 10.1126 / science.1209926
  10. ↑ Jennifer M. Hay, Sankar Subramanian, Craig D. Millar, Elmira Mohandesan, David M. Lambert (2008): Rapid molecular evolution in a living fossil. Trends in Genetics 24 (3): 106-109. doi: 10.1016 / j.tig.2007.12.002
  11. ↑ Matthias Obst, Søren Faurby, Somchai Bussarawit, Peter Funch (2012): Molecular phylogeny of extant horseshoe crabs (Xiphosura, Limulidae) indicates Paleogene diversification of Asian species. Molecular Phylogenetics and Evolution 62: 21-26. doi: 10.1016 / j.ympev.2011.08.025
  12. ↑ Christian Emig (2003): Proof that Lingula (Brachiopoda) is not a living-fossil, and emended diagnoses of the Family Lingulidae. Carnets de Géologie / Notebooks on Geology: Letter 2003/01 (CG2003_L01_CCE) online
  13. ↑ Didier Casane & Patrick Laurenti (2013): Why coelacanths are not 'living fossils'. A review of molecular and morphological data. Bioessays 35: 332-338. doi: 10.1002 / bies.201200145
  14. ^ Lionel Cavin & Guillaume Guinot (2014): Coelacanths as “almost living fossils”. frontiers in Ecology and Evolution 2: article no.49.doi: 10.3389 / fevo.2014.00049
  15. ↑ Dominic J. Bennett, Mark D. Sutton, Samuel T. Turvey (2018): Quantifying the living fossil concept. Palaeontologica Electronica, Article number: 21.1.14A. doi: 10.26879 / 750
  16. ↑ Steven Heritage, David Fernández, Hesham M. Sallam, Drew T. Cronin, Josè Manuel Esara Echube, Erik R. Seiffert: Ancient phylogenetic divergence of the enigmatic African rodent Zenkerella and the origin of anomalurid gliding . In: PeerJ. No. 4 , 2016, p. e2320 , doi : 10.7717 / peerj.2320 .

See also

Web links