Dickinsonia Costata Ontogeny
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''Dickinsonia'' is an extinct genus of
basal animal Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. ...
that lived during the late
Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...
period in what is now Australia, China, 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
bilateria The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...
n affinity, though some have suggested that it belongs to the
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, or even an "extinct
kingdom Kingdom commonly refers to: * A monarchy ruled by a king or queen * Kingdom (biology), a category in biological taxonomy Kingdom may also refer to: Arts and media Television * ''Kingdom'' (British TV series), a 2007 British television drama s ...
". It lived during the late Ediacaran (part of Precambrian). The discovery of
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
molecules in fossils of ''Dickinsonia'' lends support to the idea that ''Dickinsonia'' was an
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
.


Description

''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 in length, and from a fraction of a millimetre to a few millimetres thick. 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 In 2-dimensional geometry, a glide reflection (or transflection) is a symmetry operation that consists of a reflection over a line and then translation along that line, combined into a single operation. The intermediate step between reflection ...
symmetry rather than bilateral symmetry; thus, these " segments" are
isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...
. This glide reflection is also found in ''
Spriggina ''Spriggina'' is a genus of early bilaterian animals whose relationship to living animals is unclear. Fossils of ''Spriggina'' are known from the late Ediacaran period in what is now South Australia. ''Spriggina floundersi'' is the official fo ...
'', ''
Yorgia ''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proarti ...
'', ''
Andiva ''Andiva ivantsovi'' is a Vendian fossil, identified to be a bilaterian triploblastic animal in the Ediacaran phylum Proarticulata, known from the Winter Coast, White Sea, Russia. It was first discovered in 1977, and described as a new species ...
'', ''
Cephalonega ''Cephalonega stepanovi'' is a fossil organism from Ediacaran deposits of the Arkhangelsk Region, Russia. It was described by Mikhail A. Fedonkin in 1976 Name Its original genus name ''Onega'' comes from the Onega Peninsula of the White Sea ...
'' and other relatives of a ''Dickinsonia'' from the extinct Phylum
Proarticulata Proarticulata is a proposed phylum of extinct, bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately . The name comes from the Greek () = "before" and Articulata, i.e. ...
. The segments of ''Dickinsonia'' have been described by
Adolf Seilacher Adolf "Dolf" Seilacher (February 24, 1925 – April 26, 2014) was a German palaeontologist who worked in evolutionary and ecological palaeobiology for over 60 years. He is best known for his contributions to the study of trace fossils; constructi ...
as
self-organising Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order arises from local interactions between parts of an initially disordered system. The process can be spontaneous when suffici ...
"
pneu structure Biological or process structuralism is a school of biological thought that objects to an exclusively Darwinian or adaptationist explanation of natural selection such as is described in the 20th century's modern synthesis. It proposes instead ...
s", chambers filled with a liquid at higher than ambient pressure, analogous to a quilted
air mattress An air mattress is an inflatable mattress or sleeping pad. Due to its buoyancy, it is also often used as a water toy or flotation device, and in some countries, including the UK, is called a lilo ("Li-lo" being a specific trademark -- derived ...
. 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.


Discovery and naming

The first species and specimens of this fossil organism were first discovered in the Ediacara Member of the
Rawnsley Quartzite Rawnsley is a family name; it may refer to: ;People * Andrew Rawnsley (born 1962), British political journalist * Brenda Rawnsley (1916-2007), British arts campaigner and arts education activist * David Rawnsley (1909–1977), British art director ...
,
Flinders Ranges The Flinders Ranges are the largest mountain range in South Australia, which starts about north of Adelaide. The ranges stretch for over from Port Pirie to Lake Callabonna. The Adnyamathanha people are the Aboriginal group who have inhabi ...
in
South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
. Additional specimens of ''Dickinsonia'' are also known from the
Mogilev Formation Mogilev (russian: Могилёв, Mogilyov, ; yi, מאָלעוו, Molev, ) or Mahilyow ( be, Магілёў, Mahilioŭ, ) is a city in eastern Belarus, on the Dnieper River, about from the border with Russia's Smolensk Oblast and from the bor ...
in the Dniester River Basin of
Podolia Podolia or Podilia ( uk, Поділля, Podillia, ; russian: Подолье, Podolye; ro, Podolia; pl, Podole; german: Podolien; be, Падолле, Padollie; lt, Podolė), is a historic region in Eastern Europe, located in the west-central ...
,
Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inv ...
, the Lyamtsa, Verkhovka, Zimnegory and Yorga Formations in the
White Sea The White Sea (russian: Белое море, ''Béloye móre''; Karelian and fi, Vienanmeri, lit. Dvina Sea; yrk, Сэрако ямʼ, ''Serako yam'') is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is su ...
area of the
Arkhangelsk Region Arkhangelsk Oblast (russian: Арха́нгельская о́бласть, ''Arkhangelskaya oblast'') is a federal subject of Russia (an oblast). It includes the Arctic archipelagos of Franz Josef Land and Novaya Zemlya, as well as the Solovet ...
, Chernokamen Formation of the Central Urals,
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
, (these deposits have been dated to 567–550 Myr. ), the Dengying Formation in the Yangtze Gorges area, South China. (ca. 551–543 Ma)
Reg Sprigg Reginald Claude Sprigg, (1 March 1919 – 2 December 1994) was an Australian geologist and conservationist. At 17 he became the youngest Fellow of the Royal Society of South Australia. During 1946, in the Ediacara Hills, South Australia he di ...
, the original discoverer of the
Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-sh ...
in Australia, described ''Dickinsonia'', naming it after Ben Dickinson, then Director of Mines for
South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
, and head of the government department that employed Sprigg.


Body fossils

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. 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" on the decaying body, or perhaps it was due to the carbonate cementation of the sand. 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. Rarely, ''Dickinsonia'' have been preserved as a cast in massive sandstone lenses, where it occurs together with ''
Pteridinium ''Pteridinium'' is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota. Body plan The three-lobed body is generally flat such that only two lobes are visible. Each lobe consists of a number ...
'', ''
Rangea ''Rangea'' is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs. ''Rangea'' was the first complex Precambrian macrofossil named and described anywhere in the world. ''Rangea'' was a centimetre- ...
'' and some others. These specimens are products of events where organisms were first stripped from the sea-floor, transported and deposited within sand flow. In such cases, stretched and ripped ''Dickinsonia'' occur. The first such specimen was described as a separate genus and species, ''Chondroplon bilobatum'' and later re-identified as ''Dickinsonia''.


Trace fossils

Several
trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
s, including ''
Epibaion ''Epibaion'' is a trace fossil imprint of the Ediacaran animals of the phylum Proarticulata, which became extinct in the Precambrian. Imprints often occurring in chains, that is interpreted as a feeding trace; some chains terminate in a body foss ...
'' and ''
Phyllozoon ''Phyllozoon''(lit. "Leaf animal" in greek) is an Ediacaran imprint that resembles a proarticulatan and has been interpreted as a feeding trace. It usually occurs in long chains of imprints formed, presumably as the organism that made it moved. ...
'', 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.


Taxonomy

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


Classification

The affinities of ''Dickinsonia'' are uncertain. It has been variously interpreted as a
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
,
coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...
, polychaete worm,
turbellarian The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from to large freshwater forms more ...
, mushroom, xenophyophoran
protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
,
sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...
,
lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.chordates A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These five ...
. Genera such as ''
Yorgia ''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proarti ...
'' 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 The rangeomorphs are a form taxon of frondose Ediacaran fossils that are united by a similarity to ''Rangea''. Some researchers, such as Pflug and Narbonne, suggest that a natural taxon Rangeomorpha may include all similar-looking fossils. Ra ...
. Paleontologist Adolph Seilacher even went so far as to suggest that most of the Ediacaran fauna represents a separate
Kingdom Kingdom commonly refers to: * A monarchy ruled by a king or queen * Kingdom (biology), a category in biological taxonomy Kingdom may also refer to: Arts and media Television * ''Kingdom'' (British TV series), a 2007 British television drama s ...
termed "Vendozoa" (now: "
Vendobionta Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, i ...
") that thrived just before most of the modern multicellular animal phyla appeared in the fossil record. There is an argument that ''Dickinsonia'' is more
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
than a
sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...
, but less so than a eumetazoan. The idea that these organisms could move depends on whether ''
Epibaion ''Epibaion'' is a trace fossil imprint of the Ediacaran animals of the phylum Proarticulata, which became extinct in the Precambrian. Imprints often occurring in chains, that is interpreted as a feeding trace; some chains terminate in a body foss ...
'' is its trace fossil or just a different preservation state. 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
placozoa The Placozoa are a basal form of marine free-living (non-parasitic) multicellular organism. They are the simplest in structure of all animals. Three genera have been found: the classical ''Trichoplax adhaerens'', '' Hoilungia hongkongensis'', a ...
ns do. The
placozoa The Placozoa are a basal form of marine free-living (non-parasitic) multicellular organism. They are the simplest in structure of all animals. Three genera have been found: the classical ''Trichoplax adhaerens'', '' Hoilungia hongkongensis'', a ...
ns are simple animals which absorb food through their bottom surface ("feed through the soles of their feet") and are tentatively placed
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
ally between sponges and eumetazoa; this suggests that ''Dickinsonia'' may have been a
stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
placozoan, or somewhere more
crown A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...
-wards than sponges on the eumetazoan stem. A study of inferred growth patterns determined that ''Dickinsonia'' is a eumetazoan but a more accurate affiliation was not established. In a subsequent study Hoyal Cuthill & Han (2018) assigned ''Dickinsonia'' to the extinct animal group
Petalonamae The petalonamids (Petalonamae) are an extinct group of archaic animals typical of the Ediacaran biota, also called frondomorphs, dating from approximately 635 million years ago to 516 million years ago. They are benthic and motionless animals, ...
(placed as
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
to the Eumetazoa), which also included the genera ''
Stromatoveris ''Stromatoveris psygmoglena'' is a genus of basal petalonam from the Chengjiang Lagerstätte, Chengjiang deposits of Yunnan that was originally aligned with the fossil ''Charnia'' (strictly, the Charniomorpha) from the Ediacara biota. However, s ...
'', ''
Arborea Arborea is a town and ''comune'' in the province of Oristano, Sardinia, Italy, whose economy is largely based on agriculture and cattle breeding with production of vegetables, rice, fruit and milk (notably the local milk product Arborea). Histo ...
'' and ''
Pambikalbae ''Pambikalbae'' is a monospecific genus known from the Ediacaran Period (approximately 555 million years ago) of South Australia. Its morphology resembles the morphology of colonial cnidarians, such as sea pens or siphonophores. Description '' ...
'', as well as
rangeomorph The rangeomorphs are a form taxon of frondose Ediacaran fossils that are united by a similarity to ''Rangea''. Some researchers, such as Pflug and Narbonne, suggest that a natural taxon Rangeomorpha may include all similar-looking fossils. R ...
s and
erniettomorph The Erniettomorphs are a form of Ediacaran fossil consisting of rows of airbed-like tubes arranged along a midline with a glide symmetry. Representative genera include '' Ernietta'', '' Phyllozoon'', ''Pteridinium'', ''Swartpuntia''. Undisputed ...
s.


Interpretation as lichens and taphomorphs

Retallack (2007) proposed that some Ediacaran fossils were
lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
,
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, or
lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.paleosol In the geosciences, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The precise definition of the term in geology and paleontology is slightly different from its use in soil science. In geolo ...
s with ''Dickinsonia'' preserved in life position suggests, according to Retallack, that ''Dickinsonia'' could have lived on dry land. In addition, ''Dickinsonia'' and other Ediacaran fossils are found on and beneath eolian laminae of the kind known only on exposed sandy river banks. These proposals are not universally accepted. 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 ither noneor a maximum of only 0.23% ergosteroids, conclusively refuting the lichen hypothesis".


Paleobiology

Under Retallack's (2007) hypothesis, 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. Their mode of anchorage may have been oyster-like concretion, lichen-like rooting with
rhizine In lichens, rhizines are multicellular root-like structures, arising mostly from the lower surface. A lichen with rhizines is termed rhizinate, while a lichen lacking rhizines is termed erhizinate. Rhizines serve only to anchor the lichen to their ...
s, or fungus-like attachment to an underground network of
hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...
e. ''Dickinsonia'' displayed isometric, indeterminate growth – that is to say, they kept growing until they were covered with sediment or otherwise killed. The organisms are preserved in such a way that their resistant parts must have been a sturdy biopolymer (such as
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
) rather than a brittle mineral (such as
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
or a pyritized "death mask"). Halo-like "reaction rims" surround specimens; adjacent specimens deform, as if to avoid entering their neighbour's halo, suggesting they competed with one another. No overlapping body fossils have been found.


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, or by sitting and dissolving the underlying microbes in order to devour them. They have also been interpreted as "tumble tracks" created by an organism rolling along the sea floor, perhaps as it was buffeted by currents, and as the bases of lichens or "mushrooms arranged in
fairy ring A fairy ring, also known as fairy circle, elf circle, elf ring or pixie ring, is a naturally occurring ring or arc of mushrooms. They are found mainly in forested areas, but also appear in grasslands or rangelands. Fairy rings are detectable by ...
s". However, in some cases these trackway imprints overlap. Ridges apparently produced by the channelling of sediment in digestive tubes also indicate body disruption. Thus an alternative interpretation is that ''Epibaion'' are dead individuals dislodged into rings by frost boils in periglacial paleosols. By this view, ''Epibaion'' is not a trace fossil, but rather a decayed body fossil (a '' taphomorph'').


See also

*
List of Ediacaran genera This is a list of all described Ediacaran genera, including the Ediacaran biota. It contains 227 genera. References {{reflist, 30em * Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end o ...


References

{{Taxonbar, from=Q292078 Dipleurozoa Ediacaran life White Sea fossils Fossil taxa described in 1947