Dickinsonia

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Not to be confused with Dicksonia.

Dickinsonia
Temporal range: Late Ediacaran, 567–550 Ma
DickinsoniaCostata.jpg
Cast of Dickinsonia costata from Australia
Scientific classification e
Kingdom: Animalia
Phylum: †Proarticulata
Class: †Dipleurozoa
Family: †Dickinsoniidae
Genus: †Dickinsonia
Sprigg, 1947
Type species
†Dickinsonia costata
Sprigg, 1947
Species
  • D. costata Sprigg, 1947
  • D. lissa Wade, 1972
  • D. menneri Keller, 1976
  • D. rex Jenkins, 1992
  • D. tenuis Glaessner & Wade, 1966
Synonyms
Genus Synonymy
Species Synonymy

Dickinsonia is an extinct genus of basal animal that lived during the late Ediacaran period in what is now Australia, China, India, Russia and Ukraine. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth is consistent with a stem-group bilaterian affinity,[3] though some have suggested that it belongs to the fungi, or even an "extinct kingdom".[4][5][6] The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal.[7]

Description[]

Ontogeny of Dickinsonia costata

Dickinsonia fossils are known only in the form of imprints and casts in sandstone beds. The specimens found range from a few millimetres to about 1.4 metres (4 ft 7 in) in length, and from a fraction of a millimetre to a few millimetres thick.[8]

They are nearly bilaterally symmetric, segmented, round or oval in outline, slightly expanded to one end (i.e. egg-shaped outline). The rib-like segments are radially inclined towards the wide and narrow ends, and the width and length of the segments increases towards the wide end of the fossil. The segments are separated by a thin ridge or groove along the axis of symmetry into right and left halves. The segments are organized in an alternating pattern according to glide reflection symmetry rather than bilateral symmetry;[2][9] thus, these "segments" are isomers.[2][10] This glide reflection is also found in Spriggina, Yorgia, Andiva, Cephalonega and other relatives of a Dickinsonia from the extinct Phylum Proarticulata.[11]

The segments of Dickinsonia have been described by Adolf Seilacher as self-organising "pneu structures", chambers filled with a liquid at higher than ambient pressure, analogous to a quilted air mattress.[12][13]

Some spectacular fossils attributed to Dickinsonia appear to preserve internal anatomy, believed to represent a tract that both digested food and distributed it throughout the organism.[14]

Discovery and naming[]

Artist's reconstruction of Dickinsonia

The first species and specimens of this fossil organism was first discovered in the Ediacara Member of the , Flinders Ranges in South Australia. Additional specimens of Dickinsonia are also known from the in the Dniester River Basin of Podolia, Ukraine,[15] the , , and in the White Sea area of the Arkhangelsk Region, Chernokamen Formation of the Central Urals, Russia,[8] (these deposits have been dated to 567–550 Myr.[16][17][18]), the Dengying Formation in the Yangtze Gorges area, South China (ca. 551–543 Ma),[19] and from the Bhimbetka rock shelters in India.[20]

Reg Sprigg, the original discoverer of the Ediacaran biota in Australia,[21] described Dickinsonia, naming it[citation needed] after Ben Dickinson, then Director of Mines for South Australia, and head of the government department that employed Sprigg.

Body fossils[]

Schematic reconstructions of Dickinsonia costata, D. lissa, D. tenuis, D. menneri, D. sp. and Ivovicia rugulosa

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.[22][23] 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"[23] on the decaying body, or perhaps it was due to the carbonate cementation of the sand.[24] 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.[10][25][26]

Rarely, Dickinsonia have been preserved as a cast in massive sandstone lenses, where it occurs together with Pteridinium, Rangea and some others.[16][27][28][29] These specimens are products of events where organisms were first stripped from the sea-floor, transported and deposited within sand flow.[16][29] In such cases, stretched and ripped Dickinsonia occur. The first such specimen was described as a separate genus and species, Chondroplon bilobatum[30] and later re-identified as Dickinsonia.[1]

Trace fossils[]

Several trace fossils, including Epibaion and Phyllozoon, have been interpreted as feeding impressions of Dickinsonia and its relatives. Such fossils consist of large, rounded impressions with less relief that the usual upper side of these animals.[10][25][31]

Species[]

Since 1947, a total of nine species have been described, of which five are currently considered valid:

Species Authority Location Status Synonyms Notes
Dickinsonia brachina [32] Wade
1972		 Australia synonym of Dickinsonia tenuis
Dickinsonia costata [21] Sprigg
1947		 Australia, Russia and Ukraine valid Dickinsonia elongata
Dickinsonia minima
Dickinsonia spriggi
Papilionata eyrei 		Unlike other species, D. costata has comparatively fewer, wider segments / isomers.
Dickinsonia elongata [33] Glaessner & Wade
1966		 Australia synonym of Dickinsonia costata
Dickinsonia lissa[32] Wade, 1972 Australia valid D. lissa is extremely elongated (up to 150 mm), almost ribbon-like in shape, with numerous thin isomers. The isomers of the head area are short in comparison with those of the rest of the body. The fossil bears a distinct axial ledge consisting of two parallel bands extending from the head region to the posterior end of the body.
Dickinsonia menneri[27] Keller
1976		 Russia valid Vendomia menneri 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 [34] Sprigg
1949		 Australia synonym of Dickinsonia costata
Dickinsonia rex [35] Jenkins
1992		 Australia valid D. rex was erected for selected paratypes of D. elongata. This species is represented by only several very big specimens (up to more than 1 m in length), and does not have a distinct determination. A large size is the major reason for D. rex's species status. Individuals identified as D. rex may simply be large specimens of D. costata and or D. tenuis.
Dickinsonia spriggi [36] Harrington & Moore
1955		 Australia Synonym of Dickinsonia costata
Dickinsonia tenuis [33] Glaessner & Wade
1966		 Australia and Russia valid Dickinsonia brachina Strongly resembles D. costata, but differs from it by more narrow and numerous segments, sparingly lengthened oval form of the body.

Classification[]

"Is Dickinsonia our oldest ancestor?" Ilya Bobrovsky from the Australian National University
The structure of some Dickinsonia specimens has been interpreted as a putative "digestive–distributive" system. Image after Ivantsov 2004

The affinities of Dickinsonia are uncertain. It has been variously interpreted as a jellyfish, coral, polychaete worm, turbellarian, mushroom, xenophyophoran protist, sea anemone, lichen,[37][38] and even a close ancestor of the chordates.[39] Genera such as Yorgia and Marywadea somewhat resemble Dickinsonia, and may be related. However, it is possible that Dickinsonia falls into a group of organisms that became extinct before the Cambrian. Its construction is loosely similar to other Ediacaran organisms, and the similarity of their architecture suggests that dickinsoniamorphs may belong in a clade with Charnia and other rangeomorphs.[40] Paleontologist Adolph Seilacher even went so far as to suggest that most of the Ediacaran fauna represents a separate Kingdom termed "Vendozoa" (now: "Vendobionta") that thrived just before most of the modern multicellular animal phyla appeared in the fossil record.[5]

There is an argument that Dickinsonia is more derived than a sponge, but less so than a eumetazoan. The idea that these organisms could move depends on whether Epibaion is its trace fossil or just a different preservation state.[41] It lacks any convincing evidence for a mouth, anus or gut, and appears to have fed by absorption on its bottom surface, much like modern placozoans do. The placozoans are simple animals which absorb food through their bottom surface ("feed through the soles of their feet") and are phylogenetically between sponges and eumetazoa; this suggests that Dickinsonia may have been a stem-group placozoan, or somewhere more crown-wards than sponges on the eumetazoan stem. [42][43] A study of inferred growth patterns determined that Dickinsonia is a eumetazoan but a more accurate affiliation was not established.[44] In a subsequent study Hoyal Cuthill & Han (2018) assigned Dickinsonia to the extinct animal group Petalonamae (placed as sister group to the Eumetazoa), which also included the genera Stromatoveris, Arborea and Pambikalbae, as well as rangeomorphs and erniettomorphs.[45]


Interpretation as lichens and taphomorphs[]

Retallack (2007) proposed that some Ediacaran fossils were lichens, based on their unusual resistance to post-burial compaction.[37][46] He suggests that the decay mode of the organisms most closely resembles that of leaves, fungi, or lichens, rather than soft-bodied animals, whose bodies clot and distort as they wilt and decay.[37]

A detailed study of paleosols with Dickinsonia preserved in life position suggests, according to Retallack, that Dickinsonia could have lived on dry land.[47] In addition, Dickinsonia and other Ediacaran fossils are found on and beneath eolian laminae of the kind known only on exposed sandy river banks.[48] These proposals are not universally accepted.[49][50] A paper announcing the discovery of cholesteroids in Dickinsonia fossils states: "Lichen-forming fungi only produce ergosteroids, and even in those that host symbiotic algae, ergosteroids remain the major sterols. Dickinsonia contained [either none] or a maximum of only 0.23% ergosteroids, conclusively refuting the lichen hypothesis".

Paleobiology[]

Under Retallack's (2007) hypothesis,[37] the Dickinsonia spent most, if not all, of their lives with most of their bodies firmly anchored to the sediment, although they may have slowly moved from resting-place to resting-place.[42] Their mode of anchorage may have been oyster-like concretion, lichen-like rooting with rhizines, or fungus-like attachment to an underground network of hyphae.[37] Dickinsonia displayed isometric, indeterminate growth – that is to say, they kept growing until they were covered with sediment or otherwise killed.[37]

The organisms are preserved in such a way that their resistant parts must have been a sturdy biopolymer (such as keratin) rather than a brittle mineral (such as calcite or a pyritized "death mask").

Halo-like "reaction rims" surround specimens;[37] adjacent specimens deform, as if to avoid entering their neighbour's halo, suggesting they competed with one another.[37] No overlapping body fossils have been found.[37]

Trace fossils[]

They may be impressions the organism made while it rested on the sediment surface – perhaps by secreting slime in order to form a platform on the underlying microbial mat,[37] or by sitting and dissolving the underlying microbes in order to devour them.[37][51]

They have also been interpreted as "tumble tracks" created by an organism rolling along the sea floor, perhaps as it was buffeted by currents,[37] and as the bases of lichens or "mushrooms arranged in fairy rings".[37] However, in some cases these trackway imprints overlap. Ridges apparently produced by the channelling of sediment in digestive tubes also indicate body disruption.[10][25] Thus an alternative interpretation is that Epibaion are dead individuals dislodged into rings by frost boils in periglacial paleosols.[52] By this view, Epibaion is not a trace fossil, but rather a decayed body fossil (a ).

See also[]

References[]

  1. ^ Jump up to: a b Hofmann, Hans J. (1988). "An alternative interpretation of the Ediacaran (Precambrian) chondrophore Chondroplon Wade". Alcheringa. 12 (4): 315–318. doi:10.1080/03115518808619130.
  2. ^ Jump up to: a b c d Ivantsov, A. Yu. (2007). "Small Vendian transversely articulated fossils". Paleontological Journal. 41 (2): 113–122. doi:10.1134/S0031030107020013. S2CID 86636748.
  3. ^ Gold, D. A.; Runnegar, B.; Gehling, J. G.; Jacobs, D. K. (2015). "Ancestral state reconstruction of ontogeny supports a bilaterian affinity for Dickinsonia". Evolution & Development. 17 (6): 315–397. doi:10.1111/ede.12168. PMID 26492825. S2CID 26099557.
  4. ^ Pflug (1973). "Zur fauna der Nama-Schichten in Südwest-Afrika. IV. Mikroscopische anatomie der petalo-organisme". Palaeontographica (B144): 166–202.
  5. ^ Jump up to: a b Seilacher, Adolf (1992). "Vendobionta and Psammocorallia: lost constructions of Precambrian evolution". Journal of the Geological Society, London. 149 (4): 607–613. Bibcode:1992JGSoc.149..607S. doi:10.1144/gsjgs.149.4.0607. S2CID 128681462. Retrieved 2007-06-21.
  6. ^ McMenamin M. (1998). The Garden of Ediacara. New York: Columbia University Press. ISBN 978-0-231-10559-0. OCLC 228271905. It lived during the late Ediacaran (part of Precambrian). Dinosaurs a visual encyclopedia. New York: DK Publishing, Inc. 2018-04-03. ISBN 9781465469489.
  7. ^ Bobrovskiy, Ilya; Hope, Janet M.; Ivantsov, Andrey; Nettersheim, Benjamin J.; Hallmann, Christian; Brocks, Jochen J. (20 September 2018). "Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals". Science. 361 (6408): 1246–1249. Bibcode:2018Sci...361.1246B. doi:10.1126/science.aat7228. PMID 30237355.
  8. ^ Jump up to: a b Fedonkin M. A.; Gehling J. G.; Grey K.; Narbonne G. M.; Vickers-Rich P. (2007). The Rise of Animals. Evolution and Diversification of the Kingdom Animalia. Johns Hopkins University Press. p. 326. ISBN 978-0-8018-8679-9.
  9. ^ 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.
  10. ^ Jump up to: a b c d Ivantsov, A. Y. (2011). "Feeding traces of Proarticulata — the Vendian metazoa". Paleontological Journal. 45 (3): 237–248. doi:10.1134/S0031030111030063. S2CID 128741869.
  11. ^ A.Y. Ivantsov; M.A. Fedonkin; A.L. Nagovitsyn; M.A. Zakrevskaya (2019). "Cephalonega, a new generic name, and the system of Vendian Proarticulata". Paleontological Journal. 53 (5): 447–454. doi:10.1134/S0031030119050046. S2CID 203853224.
  12. ^ Seilacher, Adolf (1991). "Self-Organizing Mechanisms in Morphogenesis and Evolution". In Schmidt-Kittler, Norbert; Vogel, Klaus (eds.). Constructional Morphology and Evolution. Springer. pp. 251–271. doi:10.1007/978-3-642-76156-0_17. ISBN 978-3-642-76158-4.
  13. ^ Seilacher, Adolf (July 1989). "Vendozoa: Organismic construction in the Proterozoic biosphere". Lethaia. 22 (3): 229–239. doi:10.1111/j.1502-3931.1989.tb01332.x.
  14. ^ Ivantsov, A. Y. (2004). "New Proarticulata from the Vendian of the Arkhangel'sk Region" (PDF). Paleontological Journal. 38 (3): 247–253. Archived from the original (PDF) on 2007-09-27. Retrieved 2007-09-27.
  15. ^ 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.
  16. ^ Jump up to: a b c Grazhdankin, Dima (2004). "Patterns of distribution in the Ediacaran biotas: facies versus biogeography and evolution" (PDF). Paleobiology. 30 (2): 203–221. doi:10.1666/0094-8373(2004)030<0203:PODITE>2.0.CO;2.
  17. ^ Maslov A.V., Podkovyrov V.N., Grazhdankin D.V., Kolesnikov A.V. (2018). "Upper Vendian in the east, northeast and north of East European Platform: Depositional processes and biotic evolution". Litosfera. 18 (4): 520–542. doi:10.24930/1681-9004-2018-18-4-520-542.CS1 maint: uses authors parameter (link)
  18. ^ Kolesnikov A.V., Liu A.G., Danelian T., Grazhdankin D.V. (2018). "A reassessment of the problematic Ediacaran genus Orbisiana Sokolov 1976". Precambrian Research. 316: 197–205. Bibcode:2018PreR..316..197K. doi:10.1016/j.precamres.2018.08.011.CS1 maint: uses authors parameter (link)
  19. ^ Wang, Xiao-Peng; Chen, Zhe; Pang, Ke; Zhou, Chuan-Ming; Xiao, Shuhai; Wan, Bin; Yuan, Xun-Lai (2021). "Dickinsonia from the Ediacaran Dengying Formation in the Yangtze Gorges area, South China". Palaeoworld. doi:10.1016/j.palwor.2021.01.002.
  20. ^ Retallack, Gregory J.; Matthews, Neffra A.; Master, Sharad; Khangar, Ranjit G.; Khan, Merajuddin (1 February 2021). "Dickinsonia discovered in India and late Ediacaran biogeography". Gondwana Research. 90: 165–170. doi:10.1016/j.gr.2020.11.008. ISSN 1342-937X.
  21. ^ Jump up to: a b Sprigg, Reg C. (1947). "Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia" (PDF). Trans. Roy. Soc. S. Aust. 71: 212–24. Archived from the original (PDF) on 2007-09-29.
  22. ^ Ivantsov, A.Y. (2009). "A new reconstruction of Kimberella, a problematic Vendian Metazoan". Paleontological Journal. 43 (6): 601–611. doi:10.1134/S003103010906001X. S2CID 85676210.
  23. ^ Jump up to: a b Gehling, J.G. (1999). "Microbial mats in terminal Proterozoic siliciclastics; Ediacaran death masks". PALAIOS. 14 (1): 40–57. Bibcode:1999Palai..14...40G. doi:10.2307/3515360. JSTOR 3515360.
  24. ^ Serezhnikova, E.A. (2011). "Microbial binding as a probable cause of taphonomic variability of Vendian fossils: Carbonate casting?". Advances in Stromatolite Geobiology. Lecture Notes in Earth Sciences. 131. pp. 525–535. doi:10.1007/978-3-642-10415-2_31. ISBN 978-3-642-10414-5.
  25. ^ Jump up to: a b c Ivantsov, A.Yu. (2013). "Trace Fossils of Precambrian Metazoans "Vendobionta" and "Mollusks"". Stratigraphy and Geological Correlation. 21 (3): 252–264. Bibcode:2013SGC....21..252I. doi:10.1134/S0869593813030039. S2CID 128638405.
  26. ^ Runnegar, Bruce (1982). "Oxygen requirements, biology and phylogenetic significance of the late Precambrian worm Dickinsonia, and the evolution of the burrowing habit". Alcheringa: An Australasian Journal of Palaeontology. 6 (3): 223–239. doi:10.1080/03115518208565415.
  27. ^ Jump up to: a b 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.
  28. ^ Keller, B. M.; Fedonkin, M. A. (1977). "New organic fossil finds in the Precambrian Valday series along the Syuz'ma River". International Geology Review. 19 (8): 924–930. Bibcode:1977IGRv...19..924K. doi:10.1080/00206817709471091.
  29. ^ Jump up to: a b Gehling, J.G.; Droser, M.L. (2013). "How well do fossil assemblages of the Ediacara Biota tell time?". Geology. 41 (4): 447–450. Bibcode:2013Geo....41..447G. doi:10.1130/G33881.1.
  30. ^ Wade, M. (1971). "Bilateral Precambrian Chondrophores from the Ediacara Fauna, South Australia". Proceedings of the Royal Society of Victoria. 84 (1): 183–188.
  31. ^ Ivantsov, A.Y.; Malakhovskaya, Y.E. (2002). "Giant Traces of Vendian Animals" (PDF). Doklady Earth Sciences. 385 (6): 618–622. Archived from the original (PDF) on 2007-07-04. Retrieved 2008-02-24.
  32. ^ Jump up to: a b Wade, M. (1972). "Dickinsonia: Polychaete worms from the late Precambrian Ediacara fauna, South Australia". Mem. Queensl. Mus. 16 (2): 171–190.
  33. ^ Jump up to: a b Glaessner, M.F.; Wade, M. (1966). "The late Precambrian fossils from Ediacara, South Australia" (PDF). Palaeontology. 9 (4): 599.
  34. ^ 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]
  35. ^ Jenkins, R.J.F. (1992). "Functional and ecological aspects of Ediacarian assemblages". In Lipps, J.; Signor, P.W. (eds.). Origin and early evolution of the Metazoa. New York, NY: Springer. pp. 131–176. ISBN 978-0-306-44067-0. OCLC 231467647.
  36. ^ Harrington, N.J.; Moore, R.C. (1955). "Kansas Pennsylvanian and other jellyfishes". Bull. Kansas Geol. Surv. 114 (5): 153–163.
  37. ^ Jump up to: a b c d e f g h i j k l m Retallack, Gregory J. (2007). "Growth, decay and burial compaction of Dickinsonia, an iconic Ediacaran fossil" (PDF). Alcheringa: An Australasian Journal of Palaeontology. 31 (3): 215–240. doi:10.1080/03115510701484705. S2CID 17181699.
  38. ^ Retallack, Gregory J. (2004). Death, decay, and destruction of Dickinsonia. Geological Society of America 2004 Annual Meeting. Abstracts with Programs. 36. Geological Society of America. p. 521. Archived from the original on 2016-03-06.
  39. ^ Dzik, Jerzy (2000). "The origin of the mineral skeleton in chordates". In Hecht, Max Knobler; MacIntyre, Ross J.; Clegg, Michael T. (eds.). Evolutionary Biology. 31. Springer. pp. 105–146. ISBN 0-306-46178-1. Retrieved 10 February 2007 – via Google Books.
  40. ^ Brasier, M.; Antcliffe, J. (2 August 2004). "Decoding the Ediacaran enigma". Science. 305 (5687): 1115–1117. doi:10.1126/science.1102673. PMID 15326344. S2CID 128702365.
  41. ^ Retallack, Gregory J. (2016). "Ediacaran sedimentology and paleoecology of Newfoundland reconsidered". Sedimentary Geology. 333: 15–31. Bibcode:2016SedG..333...15R. doi:10.1016/j.sedgeo.2015.12.001.
  42. ^ Jump up to: a b Sperling, Erik; Vinther, Jakob; Pisani, Davide; Peterson, Kevin (2008). "A placozoan affinity for Dickinsonia and the evolution of Late Precambrian metazoan feeding modes" (PDF). In Cusack, M; Owen, A; Clark, N (eds.). Programme with Abstracts. Palaeontological Association Annual Meeting. 52. Glasgow, UK. p. 81.
  43. ^ 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.
  44. ^ Hoekzema, Renee S.; Brasier, Martin D.; Dunn, Frances S.; Liu, Alexander G. (2017-09-13). "Quantitative study of developmental biology confirms Dickinsonia as a metazoan". Proceedings of the Royal Society B. 284 (1862): 20171348. doi:10.1098/rspb.2017.1348. PMC 5597836. PMID 28904140.
  45. ^ Cuthill, Jennifer F. Hoyal; Han, Jian (2018). "Cambrian petalonamid Stromatoveris phylogenetically links Ediacaran biota to later animals" (PDF). Palaeontology (Submitted manuscript). 61 (6): 813–823. doi:10.1111/pala.12393.
  46. ^ Retallack, Gregory J. (1994). "Were the Ediacaran fossils lichens?". Paleobiology. 20: 523–544. doi:10.1017/s0094837300012975.
  47. ^ Retallack, Gregory J. (3 January 2013). "Ediacaran life on land". Nature. 493 (7430): 89–92. Bibcode:2013Natur.493...89R. doi:10.1038/nature11777. PMID 23235827.
  48. ^ Retallack, Gregory J. (2018). "Interflag sandstone laminae, a novel sedimentary structure, with implications for Ediacaran paleoenvironments". Sedimentary Geology. 379: 60–76. doi:10.1016/j.sedgeo.2018.11.003.
  49. ^ Waggoner, B.M. (1995). "Ediacaran lichens: A critique". Paleobiology. 21 (3): 393–397. doi:10.1017/s0094837300013373. JSTOR 2401174.
  50. ^ Waggoner, B.; Collins, A.G. (2004). "Reductio ad absurdum: Testing the evolutionary relationships of Ediacaran and Paleozoic problematic fossils using molecular divergence dates". Journal of Paleontology. 78 (1): 51–61. doi:10.1666/0022-3360(2004)078<0051:RAATTE>2.0.CO;2.
  51. ^ Jensen, Sören; Droser, Mary L.; Gehling, James G. (2 May 2005). "Trace fossil preservation and the early evolution of animals". Palaeogeography, Palaeoclimatology, Palaeoecology. 220 (1–2): 19–29. doi:10.1016/j.palaeo.2003.09.035.
  52. ^ Retallack, Gregory J. (2016). "Field and laboratory tests for recognition of Ediacaran paleosols". Gondwana Research. 36: 94–110. doi:10.1016/j.gr.2016.05.001.
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