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Encyclopedia > Ediacaran biota
Dickinsonia costata, an Ediacaran organism of unknown affinity, with a quilted appearance.

The Ediacaran (IPA: [ˌiːdɪˈækəɹən], formerly Vendian) biota are ancient lifeforms, of the Ediacaran Period, that represent the earliest known complex multicellular organisms. They appeared soon after the Earth thawed from the Cryogenian period's extensive glaciers, and largely disappeared soon before the rapid appearance of biodiversity known as the Cambrian explosion, which saw the first appearance in the fossil record of the basic patterns and body-plans that would go on to form the basis of modern animals. Little of the diversity of the Ediacaran biota would be incorporated in this new scheme, with a distinct Cambrian biota arising and usurping the organisms that dominated the Ediacaran fossil record. Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (2272 × 1704 pixel, file size: 1. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (2272 × 1704 pixel, file size: 1. ... Species Dickinsonia is an ancient ovoid fossil with somewhat radial tubes from a (sometimes missing) central ridge. ... The symbols of the International Phonetic Alphabet can be used to show pronounciation in English. ... The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ... Multicellular organisms are those organisms containing more than one cell, and having differentiated cells that perform specialized functions. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... One computer simulation of conditions during the Snowball Earth period. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ... For other uses, see Animal (disambiguation). ... Rainforests are among the most biodiverse ecosystems on earth Biodiversity is the variation of taxonomic life forms within a given ecosystem, biome or for the entire Earth. ...


The organisms of the Ediacaran Period first appeared around 610 million years ago and flourished until the cusp of the Cambrian 542 million years ago, when their characteristic fossil communities vanished. While rare fossils that may represent survivors have been found as late as the Middle Cambrian (510 to 500 million years ago), the earlier fossil communities disappear from the record at the end of the Ediacaran, leaving only fragments of once-thriving ecosystems, if anything.[1] Multiple hypotheses exist to explain this disappearance, including preservation bias, a changing environment, the advent of predators, and competition from other lifeforms. The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... The Middle Cambrian is an geological epoch that is part of the Cambrian Era. ... The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ... A biased sample is one that is falsely taken to be typical of a population from which it is drawn. ... A juvenile Red-tailed Hawk eating a California Vole In ecology, predation describes a biological interaction where a predator organism feeds on another living organism or organisms known as prey. ...


Some Ediacaran organisms might have been closely related to groups that would rise to prominence later; for instance, Kimberella shows some similarity to molluscs, and other organisms show bilateral symmetry, a trait unique today to the Bilateria — a huge grouping containing most of the animal kingdom. Fossilised tracks of burrowing, worm-like organisms are also likely to have been made by bilaterians. However, most non-microscopic fossils are morphologically distinct from later lifeforms and resemble discs, mud-filled bags, or quilted mattresses. Classification is difficult, and the assignment of some species even at the level of kingdom — animal, fungus, protist or something else — is uncertain: one paleontologist has even gained support for a separate kingdom Vendobionta (now renamed Vendozoa).[2] Their strange form and apparent disconnectedness from later organisms have led some to consider them a "failed experiment" in multicellular life, with later multicellular life independently re-evolving from unrelated single-celled organisms.[3] Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... In biology, bilateral symmetry is a characteristic of multicellular organisms, particularly animals. ... Illustration of the different types of symmetry of Life Forms On Earth. ... For other uses, see Animal (disambiguation). ... Ernst Haeckels presentation of a three-kingdom system (Plantae, Protista, Animalia) in his 1866 Generelle Morphologie der Organismen). ... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ... Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. ... The hierarchy of scientific classification. ... For other uses, see Animal (disambiguation). ... Subkingdom/Phyla Chytridiomycota Blastocladiomycota Neocallimastigomycota Glomeromycota Zygomycota Dikarya (inc. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... A paleontologist carefully chips rock from a column of dinosaur vertebrae. ...

The Ediacaran[53][84]
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Last Ediacaran communities
Last putative Ediacaran
First Ediacaran megafossil
Marinoan Glaciation
Aspidella discs
Charnia
Neoproterozoic
(last æon of the Precambrian)

Phanerozoic The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... The Doushantuo Formation is a lagerstätte in Guizhou Province, China that is notable for being one of the oldest fossil beds to contain highly preserved fossils. ... One computer simulation of conditions during the Snowball Earth period. ... A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... Aspidella is an Ediacaran disk shaped fossil. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... In general usage, an eon (sometimes spelled aeon) is a very long period of time. ... The Precambrian (Pre-Cambrian) is an informal name for the eons of the geologic timescale that came before the current Phanerozoic eon. ... During the Phanerozoic the biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera. ...

Axis scale: millions of years ago.

Contents

History

The first Ediacaran fossils discovered were the disc-shaped Aspidella terranovica, in 1868. Their discoverer, A. Murray, a geological surveyor, found them useful aids for correlating the age of rocks around Newfoundland.[4] However, since they lay below the "Primordial Strata" (i.e., the Cambrian strata), then thought to contain the very first signs of life, it took four years until someone, Elkanah Billings, dared to propose they could be fossils. Their simple form caused Billings' peers to dismiss his proposal, and they were instead declared gas escape structures, inorganic concretions, or even tricks played by a malicious God to promote unbelief.[4] No similar structures elsewhere in the world were then known, and the one-sided debate soon fell into obscurity.[4] In 1933, Gürich discovered specimens in Namibia,[5] but the belief that life originated in the Cambrian led to them being assigned there, and no link to Aspidella was made. In 1946, Reg Sprigg noticed "jellyfishes" in the Ediacara Hills of Australia's Flinders Ranges[6] but these rocks were believed to be Early Cambrian, so while the discovery sparked some interest, little serious attention was garnered. For other uses, see Newfoundland (disambiguation). ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... Reginald Sprigg, A.O. D.Sc. ... Ediacara Hills is a hill range in the northern Flinders Ranges of South Australia, around 650km north of Adelaide. ... Flinders Ranges is a national park in South Australia (Australia), 384 km north of Adelaide. ...


It was not until the British discovery of the iconic Charnia in 1957 that the Ediacaran was seriously considered as containing life. This frond-shaped fossil was found in England's Charnwood Forest,[7] and due to the detailed geologic mapping of the British Geological Survey there was no doubt that these fossils sat in Precambrian rocks. Palæontologist Martin Glaessner finally made the connection between this and the earlier finds,[8][9] and with a combination of improved dating of existing specimens and an injection of vigour into the search, many more instances were recognised.[10] Species Charnia wardi Charnia masoni Charnia is the genus name given to a frond-like Precambrian lifeform with segmented ridges branching alternately to the right and left from a zig-zag medial suture. ... Charnwood Forest is an upland tract in north-western Leicestershire, England. ... A geologic map is a special-purpose map made for the purpose of showing subsurface geological features. ... The British Geological Survey is a publicly-funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. ... Martin Fritz Glaessner (born 25 December 1906 in Aussig in the former Austro-Hungarian Empire, died 23 November 1989 in Melbourne, Australia) was a geologist and historical biologist. ...


However, all specimens discovered until 1967 were in coarse-grained sandstone that prevented preservation of fine details, making interpretation difficult. Mistra's discovery of fossiliferous ash-beds at the Mistaken Point assemblage in Newfoundland changed all this, as the delicate detail preserved by the fine ash allowed the description of features that were previously invisible.[11][12] Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth due to erosion by flash flooding over millions of years Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. ... Mistaken Point is a small Canadian headland on the Avalon Peninsula of Newfoundland in the province of Newfoundland and Labrador. ...


Poor communication, combined with the difficulty in correlating globally distinct formations, has led to a plethora of different names for the biota. In 1960, the French name "Ediacarien" — after the Ediacaran Hills in Southern Australia, which take their name from aborigine Idiyakra, "water is present" — was added to the competing "Sinian" and "Vendian",[13] terms for terminal-Precambrian rocks which were also applied to the lifeforms. "Ediacaran" and "Ediacarian" were subsequently applied to the epoch or period of geologic time and its corresponding rocks. In March 2004, the International Union of Geological Sciences ended the inconsistency by formally naming the terminal period of the Neoproterozoic after the Australian locality.[14] Interstate road cut through limestone and shale strata in eastern Tennessee In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. ... Languages Several hundred indigenous Australian languages (many extinct or nearly so), Australian English, Australian Aboriginal English, Torres Strait Creole, Kriol Religions Primarily Christian, with minorities of other religions including various forms of Traditional belief systems based around the Dreamtime Related ethnic groups see List of Indigenous Australian group names Indigenous... // For other uses, see time scale. ... IUGS logo The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. ... A geologic period is a subdivision of geologic time that divides an era into smaller timeframes. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ...


Preservation

The fossil Charniodiscus is barely distinguishable from the "elephant skin" texture on this cast.

All but the smallest fraction of the fossil record is comprised of the robust skeletal matter of decayed corpses. Hence, since Ediacaran biota had soft bodies and no skeletons, their abundant preservation is surprising. The absence of burrowing creatures living in the sediments undoubtedly helped;[15] since after the evolution of these organisms in the Cambrian, soft-bodied impressions were usually disturbed before they could fossilize. Image File history File links Size of this preview: 340 × 600 pixelsFull resolution (1032 × 1821 pixel, file size: 4. ... Image File history File links Size of this preview: 340 × 600 pixelsFull resolution (1032 × 1821 pixel, file size: 4. ... This article does not cite any references or sources. ...


Microbial mats

Microbial mats are areas of sediment stabilised by the presence of colonies of microbes, which secrete sticky fluids or otherwise bind the sediment particles. They appear to migrate upwards when covered by a thin layer of sediment, but this is an illusion caused by the colony's growth; individuals do not, themselves, move. If too thick a layer of sediment is deposited before they can grow or reproduce through it, parts of the colony will die, leaving behind fossils with a characteristically wrinkled "elephant skin" texture.[16] Most Ediacaran strata with the "elephant skin" texture that signifies a microbial mat contain fossils, and Ediacaran fossils are almost never found in beds that do not contain these microbial mats. Although microbial mats were once widespread, the evolution of grazing organisms in the Cambrian vastly reduced their numbers,[17] and these communities are now limited to inhospitable refugia where predators cannot survive long enough to eat them. Proposed Amazonian Refugia from Haffer, 1969 In the most basic biological sense refugia (singular: refugium) refer to locations of isolated or relict populations of once widespread animal or plant species. ...


Fossilisation

The fossils were preserved by virtue of rapid covering by ash or sand, trapping them against the mud or microbial mats on which they lived.[18] Ash beds provide more detail, and can readily be precisely dated to the nearest million years or better by means of radiometric dating.[19] However, it is more common to find Ediacaran fossils under sandy beds deposited by storms or high-energy, bottom-scraping ocean currents known as turbidites.[18] Soft-bodied organisms today almost never fossilise during such events, but the presence of widespread microbial mats aided preservation by stabilising their impressions in the sediment below.[20] Radiometric dating (often called radioactive dating) is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ... USGS image Turbidite geological formations have their origins in turbidity current deposits, deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean. ...


What is preserved?

The rate of cementation of the overlying substrate, relative to the rate of decomposition of the organism, determines whether the top or bottom surface of an organism is preserved. Most disc-shaped fossils decomposed before the overlying sediment was cemented, and the ash or sand slumped in to fill the void, leaving a cast of the underside of the organism.


Conversely, quilted fossils tend to decompose after the cementation of the overlying sediment; hence their upper surfaces are preserved. Their more resistant nature is reflected in the fact that in rare occasions, quilted fossils are found within storm beds, the high-energy sedimentation not destroying them as it would the less-resistant discs. Further, in some cases, the bacterial precipitation of minerals formed a "death mask", creating a mould of the organism.[4] Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...


Morphology

Forms of Ediacaran fossil
The earliest discovered potential embryo, preserved within an acanthomorphic acritarch. The term 'acritarch' describes a range of unclassified cell-like fossils.

Acritarchs are small organic structures found as fossils. ... Image File history File links No higher resolution available. ...

Cyclomedusa, a disc shaped fossil that has been interpreted as a microbial artefact. Metric scale.
A cast of the quilted Charnia, the first accepted complex Precambrian organism. Charnia was once interpreted as a relative of the sea-pens.
Spriggina, a possible precursor to the Trilobites, may be one of the predators that led to the demise of the Ediacaran fauna[21] and subsequent diversification of animals.[22]
A late Ediacaran trace fossil preserved on a bedding plane.

The Ediacaran biota exhibited a vast range of morphological characteristics. Size ranged from millimetres to metres; complexity from "blob-like" to intricate; rigidity from sturdy and resistant to jelly-soft. Almost all forms of symmetry were present.[18] These organisms differed from earlier fossils by displaying an organised, differentiated multicellular construction and centimetre-plus sizes. These disparate morphologies can be broadly grouped into form taxa: Cyclomedusa is an ancient circular fossil with a circular bump in the middle and having as many as 5 circular growth ridges around it. ... Image File history File linksMetadata Size of this preview: 609 × 599 pixel Image in higher resolution (1161 × 1142 pixel, file size: 395 KB, MIME type: image/jpeg) Cyclomedusa, a disc shaped fossil that has been interpreted as a microbial artefact. ... Image File history File links Size of this preview: 800 × 311 pixel Image in higher resolution (1907 × 741 pixel, file size: 354 KB, MIME type: image/jpeg) Rotated version of Image:Charnia_Half_Crop. ... Spriggina was a Vendian animal of the Ediacaran period, fossils of which have been found in the Ediacara Hills of Australia. ... Orders Agnostida Nectaspida Redlichiida Corynexochida Lichida Phacopida Subclass: Librostoma Proetida Asaphida Harpetida Ptychopariida For the robot vacuum cleaner, see Electrolux Trilobite. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ... Image File history File linksMetadata Size of this preview: 800 × 347 pixel Image in higher resolution (899 × 390 pixel, file size: 188 KB, MIME type: image/jpeg) Un-cropped and un-enhanced original File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to... Image File history File linksMetadata Size of this preview: 572 × 599 pixel Image in higher resolution (1194 × 1251 pixel, file size: 1. ... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... ‹ The template below (Unit of length) is being considered for deletion. ... The elaborate patterns on the wings of butterflies are one example of biological symmetry. ... Wastebin taxon (also called a wastebasket, or dustbin taxon) is a term used in taxonomic circles that refers to a taxon that has the sole purpose of classifying organisms that dont fit anywhere else. ...

Embryos 
Recent discoveries of Precambrian multicellular life have been dominated by reports of embryos, particularly from the Doushantuo Formation in China. Some finds[23] generated intense media excitement[24] though some have claimed they are instead inorganic structures formed by the precipitation of minerals on the inside of a hole.[25] Other "embryos" have been interpreted as the remains of the giant sulfur-reducing bacteria Thiomargarita,[26] a view which is highly contested.[27][28]
Microfossils dating from 632.5 million years ago — just 3 million years after the end of the Cryogenian glaciations — may represent embryonic 'resting stages' in the life cycle of the earliest known animals.[29]
Discs 
Circular fossils, such as Ediacaria, Cyclomedusa, and Rugoconites led to the initial identification of Ediacaran fossils as cnidaria, which include jellyfish and corals.[6] Further examination has provided alternative interpretations of all disc-shaped fossils: none is now confidently recognised as jellyfish. Alternate explanations include holdfasts, protists[30] and anemones; the patterns displayed where two meet have led to many being recognised as microbial colonies.[31][32] Useful diagnostic characters are often lacking because only the underside of the organism is preserved by fossilization.
Bags 
Fossils such as Pteridinium preserved within sediment layers resemble "mud-filled bags". The scientific community is a long way from reaching a consensus on their interpretation.[33]
Quilted organisms 
The organisms considered in Seilacher's revised definition of the Vendobionta[2] share a "quilted" appearance, and resembled an inflatable mattress. Sometimes, these quilts would be torn or ruptured prior to preservation: such damaged specimens provide valuable clues in the reconstruction process. For example, the three (or more) petaloid fronds of Swartpuntia germsi could only be recognised in a posthumously damaged specimen — usually, multiple fronds were hidden as burial squashed the organisms flat.[34]
This "rangeomorph" class of organism, including the famous Charnia and Charniodiscus, is both the most iconic of the Ediacaran biota, and the most difficult to place within the existing tree of life. The quilted structure may be derived from a shared common ancestor (synapomorphy), but if it represents the most ecologically sensible form for an organism to take, different lineages may have converged upon it (plesiomorphy).
Non-Ediacaran Ediacarans 
Some Ediacaran organisms have more complex details preserved, which has allowed them to be interpreted as possible early forms of living phyla, excluding them from some definitions of the Ediacaran biota.
The earliest such fossil is the reputed bilaterian Vernanimalcula, claimed by some, however, to represent the infilling of an egg-sac or acritarch.[25][35] Later examples, almost universally accepted as bilaterians, include the mollusc-like Kimberella,[36] Spriggina (pictured),[21] and the shield-shaped Parvancorina,[37] whose affinities are currently debated.[38]
A suite of fossils known as the Small Shelly Fossils are represented in the Ediacaran, most famously by Cloudina,[39] a shelly tube-like fossil that often shows evidence of predatory boring, suggesting that whilst predation may not have been common in the Ediacaran Period, it was at least present.
Representatives of modern taxa existed in the Ediacaran, some of which are recognisable today. Sponges, red and green algæ, protists and bacteria are all easily recognisable, with some pre-dating the Ediacaran by thousands of millions of years.
Trace fossils 
The only Ediacaran burrows are horizontal, or just below the surface. Such burrows imply the presence of motile organisms with heads, which would probably have had a bilateral symmetry. This could place them in the bilateral clade of animals.[40] Putative "burrows" dating as far back as 1100 million years may have been made by animals which fed on the undersides of microbial mats, which would have shielded them from a chemically unpleasant ocean;[41] however their uneven width and tapering ends make a biological origin difficult to defend.[42] The burrows observed imply simple behaviour, and the complex, efficient feeding traces common from the start of the Cambrian are absent. Some Ediacaran fossils, especially discs, have been interpreted tentatively as trace fossils, but this hypothesis has not gained widespread acceptance. As well as burrows, some trace fossils have been found directly associated with an Ediacaran fossil. Yorgia and Dickinsonia are often found at the end of long pathways of trace fossils matching their shape;[43] the method of formation of these disconnected and overlapping fossils largely remains a mystery. The potential mollusc Kimberella is associated with scratch marks thought to have been formed by its radula,[44] further traces from 555 million years ago appear to imply active crawling or burrowing activity.[44]

The Doushantuo Formation is a lagerstätte in Guizhou Province, China that is notable for being one of the oldest fossil beds to contain highly preserved fossils. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... Binomial name Thiomargarita namibiensis Schulz , 1999 Thiomargarita namibiensis is the largest bacterium ever discovered, with a diameter of around 0. ... Ediacaria is a medusoid fossil from the Precambrian Era, or more precisely the Ediacaran Period. ... Cyclomedusa is an ancient circular fossil with a circular bump in the middle and having as many as 5 circular growth ridges around it. ... Species Glaessner & Wade 1966 Wade 1972 A member of the Ediacaran biota which takes the form of a circular to oval impression preserved in hyporelief, six or more centimeters in diameter. ... Subphylum/Classes[1] Anthozoa — corals and sea anemones Medusozoa:[2] Cubozoa — sea wasps or box jellyfish Hydrozoa — hydroids, hydra-like animals Polypodiozoa Scyphozoa — jellyfish Staurozoa — stalked jellyfish unranked: Myxozoa - parasites Cnidaria[3] (IPA: [4]) is a phylum containing some 11,000 species of apparently simple animals found exclusively in aquatic... A holdfast is a rootlike plant structure that anchors a seaweed. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... Species see text Anemone (Anemone) (from the Gr. ... Pteridinium is a fossil found in a number of Precambrian deposits worldwide. ... A pillow top queen-size mattress. ... Swartpuntia germsi is an Ediacaran leaf shaped frond fossil, with at least three quilted petaloids and probably five or six. ... Species Charnia wardi Charnia masoni Charnia is the genus name given to a frond-like Precambrian lifeform with segmented ridges branching alternately to the right and left from a zig-zag medial suture. ... Charniodiscus is an Ediacaran fossil. ... The Tree-of-Life is a fictional plant (the ancestor of yams, with similar appearance and taste) in Larry Nivens Known Space universe, for which all Hominids have an in-built genetic craving. ... Shared characteristics that define a cladistic grouping. ... It has been suggested that Clade be merged into this article or section. ... In palaeontology, a stem group is a systematic grouping that is required to accommodate fossils in the classification of organisms. ... Extant means still existing. It is the opposite of extinct, and can be applied to species, cultures and works of culture (e. ... In biological taxonomy, a phylum (Greek plural: phyla) is a taxon in the rank below kingdom and above class. ... The oldest known examples of a bilaterian, bilateral animals. ... Acritarchs are small organic structures found as fossils. ... Kimberella quadrata is a fossil animal from the Ediacaran or Vendian fauna. ... Spriggina was a Vendian animal of the Ediacaran period, fossils of which have been found in the Ediacara Hills of Australia. ... Species Parvancorina is a genus of shield-shaped Ediacaran fossils. ... Small shelly fossils is a name for an assemblage of fossils preserved in phosphate. ... Cloudinids (Cloudinia) are an extinct animal phylum that formed small tubelike or conical fossils consisting of cup-in-cup segments of calcareous material. ... Classes Calcarea Hexactinellida Demospongiae The sponges or poriferans (from Latin porus pore and ferre to bear) are animals of the phylum Porifera. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... A fossilized dinosaur footprint at Clayton Lake State Park, New Mexico. ... Illustration of the different types of symmetry of Life Forms On Earth. ... For other uses, see Animal (disambiguation). ... Yorgia waggoneri is a fossil from the Ediacaran period. ... Species Dickinsonia is an ancient ovoid fossil with somewhat radial tubes from a (sometimes missing) central ridge. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Transverse view of the buccal cavity with the radula Radula types chart. ...

Classification and interpretation

Classification of the Ediacarans is difficult, and hence a variety of theories exist as to their placement on the tree of life.

A sea-pen, a cnidarian bearing a passing resemblance to Charnia

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Cnidarians

Since the most primitive metazoans — multi-cellular animals in possession of a nervous system — are recognised as cnidarians, the first attempt to categorise these fossils designated them as jellyfish and sea-pens.[45] However, detailed study of their growth pattern has discounted this hypothesis.[46] Animalia redirects here. ... The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. ... Classes Anthozoa - Corals and sea anemones Cubozoa - Sea wasps or box jellyfish Hydrozoa - Hydroids, hydra-like animals Scyphozoa - Jellyfish Cnidaria is a phylum containing some 10,000 species of relatively simple animals found exclusively in aquatic environments (most species are marine). ... For other uses, see Jellyfish (disambiguation). ... Families Suborder Sessiliflorae Anthoptilidae Chunellidae Echinoptilidae Funiculinidae Kophobelemnidae Protoptilidae Renillidae Scleroptilidae Stachyptilidae Umbellulidae Veretillidae Suborder Subselliflorae Pennatulidae Pteroeididae Virgulariidae Sea Pens are colonial marine cnidarians belonging to the order Pennatulacea. ...


"The dawn of animal life"

Martin Glaessner proposed in his 1985 book "The dawn of animal life" that the Ediacaran biota were early stem group members of all modern phyla, and were unrecognisable because they had yet to evolve the characteristic features we use in modern classification.[47] Adolf Seilacher responded by suggesting that the Ediacaran sees animals usurping giant protists as the dominant life form.[48] Martin Fritz Glaessner (born 25 December 1906 in Aussig in the former Austro-Hungarian Empire, died 23 November 1989 in Melbourne, Australia) was a geologist and historical biologist. ... In palaeontology, a stem group is a systematic grouping that is required to accommodate fossils in the classification of organisms. ... Adolf Dolf Seilacher (b. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all...


Mark McMenamin goes one step further: he claims that Ediacarans did not possess an embryonic stage, and thus could not be animals. He believes that they independently evolved a nervous system and brains, meaning that "the path toward intelligent life was embarked upon more than once on this planet."[30] Mark McMenamin is a professor of geology at Mt. ... For other uses, see Embryo (disambiguation). ...


New phylum

Seilacher most famously suggested that the Ediacaran organisms represented a unique and extinct grouping of related forms descended from a common ancestor (clade) and created the kingdom Vendozoa,[49][50] named after the now-obsolete Vendian era. He later excluded fossils identified as metazoans and relaunched the phylum "Vendobionta". A clade is a term belonging to the discipline of cladistics. ... Ernst Haeckels presentation of a three-kingdom system (Plantae, Protista, Animalia) in his 1866 Generelle Morphologie der Organismen). ... The Vendian biota (also known as Vendian forms, Vendian fauna(s), and Vendazoa) are a group of ancient lifeforms that are found in rocks a bit older than the Cambrian faunas that represent the oldest fossils of classical paleontology. ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ...


He described the Vendobionta as quilted cnidarians lacking stinging cells. This absence precludes the current cnidarian method of feeding, so Seilacher suggested that the organisms may have survived by symbiosis with photosynthetic or chemoautotrophic organisms.[51] Classes Anthozoa - Corals and sea anemones Cubozoa - Sea wasps or box jellyfish Hydrozoa - Hydroids, hydra-like animals Scyphozoa - Jellyfish Cnidaria is a phylum containing some 10,000 species of relatively simple animals found exclusively in aquatic environments (most species are marine). ... Cnidocytes, also known as cnidoblasts or nematocytes, are prey-capture and defensive cells unique to and present in all animals of the phylum Cnidaria (corals, sea anemones, hydrae, jellyfish etc. ... Meat Ants harvest Leaf Hoppers for their honey dew. ... The leaf is the primary site of photosynthesis in plants. ... This page is a candidate to be moved to Wiktionary. ...

Lichen with a 3D structure may be preserved in a similar fashion to wood.

Image File history File linksMetadata Kananakislichen. ... Image File history File linksMetadata Kananakislichen. ...

Lichens

Gregory Retallack's hypothesis that Ediacaran organisms were lichens[52] has failed to gain wide-spread acceptance. He argues that the fossils are not as squashed as jellyfish fossilised in similar situations, and their relief is closer to petrified wood. He points out the chitinous walls of lichen colonies would provide a similar resistance to compaction, and claims the large size of the organisms — sometimes over a metre across, far larger than any of the preserved burrows — also hints against a classification with the animals. Lichenes from Ernst Haeckels Artforms of Nature, 1904 Lichens are symbiotic associations of a fungus (the mycobiont) with a photosynthetic partner (the photobiont also known as the phycobiont) that can produce food for the lichen from sunlight. ... Petrified log at the Petrified Forest National Park A petrified tree from California Petrified wood is a type of fossil: it consists of fossil wood where all the organic materials have been replaced with minerals (most often a silicate, such as quartz), while retaining the original structure of the wood. ... Structure of the chitin molecule, showing two of the N-Acetylglucosamine units that repeat to form long chains in beta-1,4 linkage. ...


Other interpretations

Almost every possible phylum has been used to accommodate the Ediacara biota,[53] from algæ,[54] to protists known as foraminifera,[55] to fungi[56] to bacterial or microbial colonies,[31] to hypothetical intermediates between plants and animals.[57] Since representatives of almost all modern phyla were in existence by the Middle Cambrian, it is probable that the precursors of many phyla would be represented in the Ediacaran. The accumulation of random changes in sequences of DNA — assumed to accumulate at a constant rate — can be used to estimate the time that two lineages shared a common ancestor, and applying this technique to modern phyla produces estimated divergence dates long before the Cambrian.[58] More recent use of molecular clocks, scaled on phyla well represented in the fossil record, show divergence points that are remarkably in keeping with Ediacaran and Cambrian fossil record. If this is indeed the case, attempts to group everything alive in the Ediacara biota into one phylum are doomed to failure. A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Typical phyla Rhodophyta (red algae) Chromista Heterokontophyta (heterokonts) Haptophyta Cryptophyta (cryptomonads) Alveolates Pyrrhophyta (dinoflagellates) Apicomplexa Ciliophora (ciliates) Excavates Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Amoebozoa Choanozoa Many others; classification varies The Kingdom Protista or Protoctista is one of the commonly recognized biological kingdoms, including all the eukaryotes except for... Orders Allogromiida Carterinida Fusulinida - extinct Globigerinida Involutinida - extinct Lagenida Miliolida Robertinida Rotaliida Silicoloculinida Spirillinida Textulariida incertae sedis    Xenophyophorea    Reticulomyxa The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands that branch and merge to form a dynamic net. ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... The molecular clock (based on the molecular clock hypothesis (MCH)) is a technique in genetics, which researchers use to date when two species diverged. ...


Origin

It took 4 billion years from the formation of the Earth for the Ediacaran fossils to first appear, 655 million years ago. Whilst putative fossils are reported from 3,460 million years ago,[59][60] the first uncontroversial evidence for life is found 2,700 million years ago,[61] and cells with nuclei certainly existed by 1,200 million years ago:[62] why did it take so long for forms with an Ediacaran grade of organisation to appear?


It could be that no special explanation is required: the slow process of evolution simply required 4 billion years to accumulate the necessary adaptations. Indeed, there does seem to be a slow increase in the maximum level of complexity seen over this time, with more and more complex forms of life appearing as time progresses, with traces of earlier semi-complex life such as Nimbia, found in the 610 million-year-old Twitya formation,[63] possibly displaying the most complex morphology of the time. The evolution of complexity is an important outcome of the process of evolution. ... Nimbia occlusa is a form of Ediacaran fossil shaped like a circular or oval disk. ...

Global ice sheets may have delayed or prevented the establishment of multicellular life.

The alternative train of thought is that it was simply not advantageous to be large until the appearance of the Ediacarans: the environment favoured the small over the large. Examples of such scenarios today include plankton, whose small size allows them to reproduce rapidly to take advantage of ephemerally abundant nutrients in algal blooms. But for large size never to be favourable, the environment would have to be very different indeed. Image File history File linksMetadata Download high-resolution version (937x688, 137 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Antarctica Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Image File history File linksMetadata Download high-resolution version (937x688, 137 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Antarctica Metadata This file contains additional information, probably added from the digital camera or scanner used to create...


A primary size-limiting factor is the amount of atmospheric oxygen. Without a complex circulatory system, low concentrations of oxygen cannot reach the centre of an organism quickly enough to supply its metabolic demand. General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... Diagram of the human circulatory system. ...


On the early earth, reactive elements such as iron and uranium existed in a reduced form; these would react with any free oxygen produced by photosynthesising organisms. Oxygen would not be able to build up in the atmosphere until all the iron had rusted, and other reactive elements had been oxidised. Donald Canfield detected records of the first significant quantities of atmospheric oxygen just before the first Ediacaran fossils appeared[64] — and the presence of atmospheric oxygen was soon heralded as a possible trigger for the Ediacaran radiation.[65] Oxygen seems to have accumulated in two pulses; the rise of small, sessile (stationary) organisms seems to correlate with an early oxygenation event, with larger and mobile organisms appearing around the second pulse of oxygenation.[66] The resolution of the fossil record is too low to make this assertion definite, and current research seeks to accurately determine the role that oxygen may have played.[67] Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... The leaf is the primary site of photosynthesis in plants. ... Donald Canfield is a geologist born in 1958, most famous for his work on ancient ocean chemistry. ... Four of the 13 finch species found on the Galápagos Archipelago, and thought to have evolved by an adaptive radiation that diversified their beak shapes to adapt them to different food sources. ...


Periods of intense cold have also been suggested as a barrier to the evolution of multicellular life. The earliest known embryos, from China's Doushantuo Formation, appear just a million years after the Earth emerged from a global glaciation, suggesting that ice cover and cold oceans may have prevented the emergence of multicellular life.[68] Potentially, complex life may have evolved before these glaciations, and been wiped out. However, the diversity of life in modern Antarctica has sparked disagreement over whether cold temperatures increase or decrease the rate of evolution. A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... The Doushantuo Formation is a lagerstätte in Guizhou Province, China that is notable for being one of the oldest fossil beds to contain highly preserved fossils. ... One computer simulation of conditions during the Snowball Earth period. ...


Disappearance

The low resolution of the fossil record means that the disappearance of the Ediacarans remains something of a mystery. There appears to have been a relatively abrupt disappearance at the end of the Ediacaran period; reports of Cambrian "Ediacarans" are not universally accepted. The cause — and reality — of this disappearance is open to debate.


Preservation bias

The sudden vanishing of Ediacaran fossils at the Cambrian boundary could simply be because conditions no longer favoured the fossilisation of Ediacaran organisms, which may have continued to thrive unpreserved.[16] However, if they were common, more than the occasional specimen[1] might be expected in exceptionally preserved fossil assemblages (Konservat-Lagerstätten) such as the Burgess Shale and Chengjiang[69] — unless such assemblages represent an environment never occupied by the Ediacaran biota, or unsuitable conditions for their preservation. Lagerstätten (German; singular Lagerstätte; literally place of storage, resting place) are sedimentary deposits that exhibit extraordinary fossil richness or completeness. ... Hallucigenia sparsa, one of the organisms unique to the Burgess Shale. ... The Maotianshan shale is a lower Cambrian (Atdabanian) rock formation, of ca 522 Mya, now lying exposed in the Yunnan Province of China in the villages of Ercaicun and Chengjiang near the city of Kunming. ...

Kimberella may have had a predatory or grazing lifestyle.

Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ...

Predation and grazing

By the Early Cambrian, organisms higher in the food chain caused the microbial mats to largely disappear. These grazers first appeared as the Ediacaran biota started to decline, which may suggest that they destabilised the microbial substrate, leading to displacement or detachment of the biota; or that the destruction of the mat destabilised the ecosystem. In ecology, the trophic level (Greek trophē, food) is the position that an organism occupies in a food chain - what it eats, and what eats it. ... Look up substrate in Wiktionary, the free dictionary. ...


Alternatively, skeletonised animals could have fed directly on the relatively undefended Ediacaran biota.[30] However, the existence in the Ediacaran of the recognized predator Kimberella suggests that the biota had already had limited exposure to predation.[36] This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Kimberella quadrata is a fossil animal from the Ediacaran or Vendian fauna. ...

Cambrian animals such as Waptia may have competed with, or fed upon, Ediacaran lifeforms.

Image File history File linksMetadata Size of this preview: 800 × 531 pixel Image in higher resolution (834 × 554 pixel, file size: 200 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Size of this preview: 800 × 531 pixel Image in higher resolution (834 × 554 pixel, file size: 200 KB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Waptia fieldensis was a small, shrimp-like pseudo-crustacean that lived during the Middle Cambrian about 500 million years ago [1][2] Tirami su ...

Competition

It is possible that increased competition due to the evolution of key innovations amongst other groups, perhaps as a response to predation,[15] drove the Ediacaran biota from their niches. However, this argument has not successfully explained similar phenomena. For instance, the bivalve molluscs' "competitive exclusion" of brachiopods was eventually deemed to be a coincidental result of two unrelated trends.[70] Orders Subclass Anomalosdesmata Pholadomyoida Subclass Heterodonta - clams, zebra mussels †Cycloconchidae Hippuritoida †Lyrodesmatidae Myoida PENIS †Redoniidae Veneroida Subclass Paleoheterodonta Trigonioida; see Superfamily Trigoniacea Unionoida - freshwater mussels Subclass Protobranchia Nuculoida †Praecardioida Solemyoida Subclass Pteriomorphia - oysters, mussels Arcoida Mytiloida Ostreoida Pterioida Bivalves are mollusks belonging to the class Bivalvia. ... Subphyla and classes See Classification Brachiopods (from Latin brachium, arm + New Latin -poda, foot) are a phylum of animals. ...


Change in environmental conditions

While it is difficult to infer the effect of changing planetary conditions on organisms, communities and ecosystems, great changes were happening at the end of the Precambrian and the start of the Early Cambrian. The breakup of the supercontinents,[71] rising sea levels (creating shallow, "life-friendly" seas),[72] a nutrient crisis,[73] fluctuations in atmospheric composition, including oxygen and carbon dioxide levels,[74] and changes in ocean chemistry[75] (promoting biomineralisation)[76] could all have played a part. Depiction of Rodinia at time of initial breakup. ... Biomineralisation is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. ...


Assemblages

Ediacaran-type fossils are recognised globally in 25 localities[14] and a variety of depositional conditions, and are commonly grouped into three main types, named after typical localities. Deposition, also known as sedimentation, is the geological process whereby material is added to a landform. ...


Ediacara-type assemblage

The Ediacara-type assemblage is named after Australia's Ediacara Hills, and consist of fossils preserved in prodeltaic facies (areas near the mouths of rivers). They are typically found in interbedded sandy and silty layers formed below the normal base of wave-related water motion, but in waters shallow enough to be affected by wave motion during storms. Most fossils are preserved as imprints in microbial mats, but a few are preserved within sandy units.[77] Nile River delta, as seen from Earth orbit. ... The term facies was introduced by the Swiss geologist Amanz Gressly in 1838 and was part of his significant contribution to the foundations of modern stratigraphy (see Cross and Homewood 1997), which replaced the earlier notions of Neptunism. ...

Biota ranges[77]
view  talk  edit
Axis scale: millions of years ago, dated with U/Pb of zircons

Nama-type assemblage

The Nama assemblage is best represented in Namibia. Three-dimensional preservation is most common, with organisms preserved in sandy beds containing internal bedding. Dima Grazhdankin believes that these organisms represent burrowing organisms,[33] while Guy Narbonne maintains they were surface dwellers.[78] These beds are sandwiched between units comprising interbedded sandstones, siltstones and shales, with microbial mats, where present, usually containing fossils. The environment is interpreted as sand bars formed at the mouth of a delta's distributaries.[77] Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. ... Nile River delta, as seen from Earth orbit. ... distributary in Else and Hase at Melle A seasonal Distributary of the Kaveri river on the Kaveri delta, near Nannilam, India. ...


Avalon-type assemblage

The Avalon-type assemblage is defined at Mistaken Point in Canada, the oldest locality with a large quantity of Ediacaran fossils.[79] The assemblage is easily dated because it contains many fine ash-beds, which are a good source of zircons used in the uranium-lead method of radiometric dating. These fine-grained ash beds also preserve exquisite detail. Mistaken Point is a small Canadian headland on the Avalon Peninsula of Newfoundland in the province of Newfoundland and Labrador. ... Zircon is a mineral belonging to the group of nesosilicates. ... Radiometric dating (often called radioactive dating) is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ...


The biota comprises deep sea dwelling rangeomorphs[80] such as Charnia, all of which share a fractal growth pattern. They were probably preserved in situ (without post-mortem transportation), although this point is not universally accepted. The assemblage, while less diverse than the Ediacara- or Nama-types, resembles Carboniferous suspension-feeding communities, which may suggest filter feeding[81] — by most interpretations, the assemblage is found in water too deep for photosynthesis. The low diversity may reflect the depth of water — which would restrict speciation opportunities — or it just be too young for evolution to rich biota. Opinion is currently divided between these conflicting hypotheses.[77] Rangeomorphs are soft-bodied creatures, neither animals nor plants that appeared 575 million years ago at the beginning of the Ediacaran period. ... The boundary of the Mandelbrot set is a famous example of a fractal. ... The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ... Filter feeders (also known as suspension feeders) are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized structure, such as the baleen of baleen whales. ... Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...


Significance of assemblages

In the White Sea region of Russia, all three assemblage types have been found in close proximity. This, and the faunas' considerable temporal overlap, makes it unlikely that they represent evolutionary stages or temporally distinct communities. Since they are globally distributed — described on all continents except Antarctica — geographical boundaries do not appear to be a factor;[82] the same fossils are found at all palæolatitudes (the latitude where the fossil was created, accounting for continental drift) and in separate sedimentary basins.[77] Map of the White Sea Two satellite photos of the White Sea The White Sea (Russian: ) is an inlet of the Barents Sea on the North Western coast of Russia. ... In ecology, a community is an assemblage of populations of different species, interacting with one another. ... This article is about the geographical term. ... Plates in the crust of the earth, according to the plate tectonics theory Continental drift refers to the movement of the Earths continents relative to each other. ... The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. ...


It is most likely that the three assemblages mark organisms adapted to survival in different environments, and that any apparent patterns in diversity or age are in fact an artefact of the few samples that have been discovered — the timeline (right) demonstrates the paucity of Ediacaran fossil-bearing assemblages.


As the Ediacaran biota represent an early stage in multicellular life's history, it is unsurprising that not all possible modes of life are occupied. It has been estimated that of 92 potentially possible modes of life — combinations of feeding style, tiering and motility — no more than a dozen are occupied by the end of the Ediacaran. Just four are represented in the Avalon assemblage.[83] The lack of large-scale predation and vertical burrowing are perhaps the most significant factors limiting the ecological diversity; the emergence of these during the Early Cambrian allowed the number of lifestyles occupied to rise to 30. Guilds are groups of organisms sharing a common way of life. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ...


Further reading

  • Simon Conway Morris (7 October 1999). The Crucible of Creation: The Burgess Shale and the Rise of Animals. ISBN 978-0-19-286202-0. 
  • Mark McMenamin (1998). The Garden of Ediacara: Discovering the First Complex Life, 368pp. ISBN 978-0231105590. 
  • Derek Briggs & Peter Crowther (Editors) (2001). Palæobiology II: A synthesis, Chapter 1. ISBN 0-632-05147-7.  Good further reading for the keen - includes many interesting chapters with macroevolutionary theme.

External links

See also

This is a list of all known genera of Ediacaran biota. ... This article does not adequately cite its references or sources. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ...

References

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