Dickinsonia
Dickinsonia | |
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Cast of Dickinsonia costata from Australia | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | †Proarticulata |
Class: | †Dipleurozoa |
Family: | †Dickinsoniidae |
Genus: | †Dickinsonia Sprigg, 1947 |
Type species | |
†Dickinsonia costata Sprigg, 1947
| |
Species | |
| |
Synonyms | |
D. costata Synonymy
D. tenuis Synonymy
|
Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity,[3] though various other affinities have been proposed.[4][5][6] The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal,[7] though these results have been questioned.[8]
Description
Dickinsonia fossils are known only in the form of imprints and casts in sandstone beds. The specimens found range from a few
The body of Dickinsonia is suggested to have been sack-like, with the outer layer being made of a resistant but unmineralised material.[13] Some specimens from Russia show the presence of branched internal structures.[15][13] Some authors have suggested that the underside of the body bore cilia, as well as infolded pockets.[13]
Dickinsonia is suggested to have grown by adding a new pair of segments/isomers at the end opposite the unpaired "anterior most unit".[11][16] Dickinsonia probably exhibited indeterminate growth (having no maximum size), though it is suggested that the addition of new segments slowed down later in growth.[17] Deformed specimens from Russia indicate that individuals of Dickinsonia could regenerate after being damaged.[16]
Ecology
Dickinsonia is suggested to have been a mobile marine organism that lived on the seafloor and fed by consuming microbial mats growing on the seabed using structures present on its underside. Dickinsonia-shaped trace fossils, presumed to represent feeding impressions, sometimes found in chains demonstrating this behaviour have been observed.[13] These trace fossils have been assigned to the genus Epibaion.[12][18][19] A 2022 study suggested that Dickinsonia temporarily adhered itself to the seafloor by the use of mucus, which may have been an adaptation to living in very shallow water environments.[20]
Discovery
The first species and specimens of this fossil organism were first discovered in the Ediacara Member of the
Taphonomy
As a rule, Dickinsonia fossils are preserved as negative impressions ("death masks") on the bases of sandstone beds. Such fossils are imprints of the upper sides of the benthic organisms that have been buried under the sand.[28][29] The imprints formed as a result of cementation of the sand before complete decomposition of the body. The mechanism of cementation is not quite clear; among many possibilities, the process could have arisen from conditions which gave rise to pyrite "death masks"[29] on the decaying body, or perhaps it was due to the carbonate cementation of the sand.[30] The imprints of the bodies of organisms are often strongly compressed, distorted, and sometimes partly extend into the overlying rock. These deformations appear to show attempts by the organisms to escape from the falling sediment.[12][18][31]
Rarely, Dickinsonia have been preserved as a cast in massive sandstone lenses, where it occurs together with Pteridinium, Rangea and some others.[32][33][34][35] These specimens are products of events where organisms were first stripped from the sea-floor, transported and deposited within sand flow.[32][35] In such cases, stretched and ripped Dickinsonia occur. The first such specimen was described as a separate genus and species, Chondroplon bilobatum[36] and later re-identified as Dickinsonia.
Taxonomy
Species
Since 1947, a total of nine species have been described, of which three are currently considered valid:[37]
Species | Authority | Location | Status | Notes |
---|---|---|---|---|
Dickinsonia brachina [38] | Wade, 1972 | Australia | invalid | Synonym of Dickinsonia tenuis |
Dickinsonia costata [39] | Sprigg, 1947 | Australia, Russia and Ukraine | valid | Unlike other species, D. costata has comparatively rounded body and fewer, wider segments / isomers. |
Dickinsonia elongata [40] | Glaessner & Wade, 1966 | Australia | invalid | Synonym of Dickinsonia costata |
Dickinsonia lissa[38] | Wade, 1972 | Australia | invalid | Synonym of Dickinsonia tenuis |
Dickinsonia menneri[41] | Keller, 1976 | Russia | valid | D. menneri is a small organism up to 8 mm in length, and strongly resembles juvenile specimens of D. costata with its small number of isomers and well-marked head. D. menneri differs from juvenile D. costata by its slightly more elongated form.
Originally classified as Vendomia, it was re-identified as Dickinsonia by Ivantsov (2007)[2] |
Dickinsonia minima [42] | Sprigg, 1949 | Australia | invalid | Synonym of Dickinsonia costata |
Dickinsonia rex [43] | Jenkins, 1992 | Australia | invalid | Synonym of Dickinsonia tenuis |
Dickinsonia spriggi [44] | Harrington & Moore, 1955 | Australia | invalid | Synonym of Dickinsonia costata |
Dickinsonia tenuis [40] | Glaessner & Wade, 1966 | Australia and Russia | valid | Strongly resembles D. costata, but differs from it by more narrow and numerous segments, sparingly lengthened oval form of the body. |
A claimed specimen of Dickinsonia from India was later determined to be the remains of a beehive.[45]
External relationships
Dickinsonia is classified as part of the group
References
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: CS1 maint: numeric names: authors list (link - ^ a b c Ivantsov, A. Yu (2012). "Becoming metamery and bilateral symmetry in Metazoa: way of Proarticulata". Morphogenesis in the Individual and Historical Development: Symmetry and Asymmetry.: 16–17.
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- ^ Eig, Karsten. "EDIACARANS: THE FOSSILS THAT SHOULD NOT BE THERE". Adventures in geology - Karsten Eig.
- ^ Fedonkin, M. A. (1983). "Non-skeletal fauna of Podoloia, Dniester River valley". In Velikanov, V. A.; Assejeva, E. A.; Fedonkin, M. A. (eds.). The Vendian of the Ukraine (in Russian). Kiev: Naukova Dumka. pp. 128–139.
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- ^ Wade, M. (1971). "Bilateral Precambrian Chondrophores from the Ediacara Fauna, South Australia". Proceedings of the Royal Society of Victoria. 84 (1): 183–188.
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- ^ a b Wade, M. (1972). "Dickinsonia: Polychaete worms from the late Precambrian Ediacara fauna, South Australia". Mem. Queensl. Mus. 16 (2): 171–190.
- ^ Sprigg, Reg C. (1947). "Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia" (PDF). Trans. R. Soc. S. Aust. 71: 212–24. Archived from the original (PDF) on 2007-09-29.
- ^ a b Glaessner, M.F.; Wade, M. (1966). "The late Precambrian fossils from Ediacara, South Australia" (PDF). Palaeontology. 9 (4): 599.
- ^ Keller, B.M.; Fedonkin, M.A. (1976). "New records of fossils in the Valdaian group of the precambrian on the Syuz'ma River" (PDF). Izvestiya Akademii Nauk SSR. Seriya Geologicheskaya (in Russian). 3: 38–44. Archived from the original (PDF) on 2007-09-27.
- ^ Sprigg, R.C. (1949). "Early Cambrian "jellyfishes" of Ediacara, South Australia, and Mount John, Kimberley District, Western Australia" (PDF). Transactions of the Royal Society of South Australia. 73: 72–99.[permanent dead link]
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- ^ Harrington, N.J.; Moore, R.C. (1955). "Kansas Pennsylvanian and other jellyfishes". Bull. Kansas Geol. Surv. 114 (5): 153–163.
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- ^ Sperling, Erik; et al. (2008). "A placozoan affinity for Dickinsonia and the evolution of late Precambrian metazoan feeding modes". Geological Society of America. Abstracts with Programs. 40 (6): 508. Archived from the original on 2018-02-28. Retrieved 2008-10-27.
- ^ J.W. Valentine Dickinsonia as a polypoid organism Paleobiology, 18 (1992), pp. 378-382