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Adolf Seilacher has suggested the Ediacaran sees animals usurping giant protists as the dominant life form. A recent genetic study suggested that the xenophyophores are a specialised group of Foraminifera. There are approximately 42 recognised species in 13 genera and 2 orders; one of which, Syringammina fragilissima , is among the largest known protozoans at up to 20 centimetres in diameter. Seilacher has 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, [78] [79] named after the now-obsolete Vendian era.

He later excluded fossils identified as metazoans and relaunched the phylum "Vendobionta". 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.

Greg Retallack 's hypothesis that Ediacaran organisms were lichens [83] [84] has been controversial [85] [86] He argues that the fossils are not as squashed as known fossil jellyfish, and their relief is closer to compressed woody branches whose compaction can be estimated as compressed cylinders.

He points out the chitinous walls of lichen colonies would provide a similar resistance to compaction, and claims the large size of the organisms up to 1. Thin sections of Ediacaran fossils show lichen-like compartments and hypha-like wisps of ferruginized clay [82]. Finally, Ediacaran fossils from classic localities of the Flinders Ranges have been found in growth position within red calcareous and gypsiferous paleosols , interpreted as soils of well-drained temperate desert soils.

Several classifications have been used to accommodate the Ediacaran biota at some point, [88] from algae , [89] to protozoans , [90] to fungi [91] to bacterial or microbial colonies, [44] to hypothetical intermediates between plants and animals. A new extant genus discovered in , Dendrogramma , which appears to be a basal metazoan but of unknown taxonomic placement, has been noted to have similarities with the Ediacaran fauna.

It could be that no special explanation is required: The alternative train of thought is that it was simply not advantageous to be large until the appearance of the Ediacarans: 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. 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.

On the early Earth, reactive elements, such as iron and uranium , existed in a reduced form that 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 producing banded iron formations , and all the other reactive elements had been oxidised. 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.

However, the diversity of life in modern Antarctica has sparked disagreement over whether cold temperatures increase or decrease the rate of evolution. In early a team analysed the range of basic body structures "disparity" of Ediacaran organisms from three different fossil beds: They found that, while the White Sea assemblage had the most species, there was no significant difference in disparity between the three groups, and concluded that before the beginning of the Avalon timespan these organisms must have gone through their own evolutionary "explosion", which may have been similar to the famous Cambrian explosion.

The paucity of Ediacaran fossils after the Cambrian could simply be due to conditions that no longer favoured the fossilisation of Ediacaran organisms, which may have continued to thrive unpreserved. It is suggested that by the Early Cambrian, organisms higher in the food chain caused the microbial mats to largely disappear. If these grazers first appeared as the Ediacaran biota started to decline, then it 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, causing extinctions.

Alternatively, skeletonised animals could have fed directly on the relatively undefended Ediacaran biota. There is however little evidence for any trace fossils in the Ediacaran Period, which may speak against the active grazing theory.

Further, the onset of the Cambrian Period is defined by the appearance of a worldwide trace fossil assemblage, quite distinct from the activity-barren Ediacaran Period. It is possible that increased competition due to the evolution of key innovations among other groups, perhaps as a response to predation, [] 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.

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 , [] rising sea levels creating shallow, "life-friendly" seas , [] a nutrient crisis, [] fluctuations in atmospheric composition, including oxygen and carbon dioxide levels, [] and changes in ocean chemistry [] promoting biomineralisation [] could all have played a part.

Ediacaran-type fossils are recognised globally in 25 localities [23] and a variety of depositional conditions, and are commonly grouped into three main types, known as assemblages and named after typical localities. Each assemblage tends to occupy its own region of morphospace, and after an initial burst of diversification changes little for the rest of its existence. The Avalon-type assemblage is defined at Mistaken Point in Canada, the oldest locality with a large quantity of Ediacaran fossils.

These fine-grained ash beds also preserve exquisite detail. Constituents of this biota appear to survive through until the extinction of all Ediacarans at the base of the Cambrian. One interpretation of the biota is as deep-sea-dwelling rangeomorphs [] 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. Opinion is currently divided between these conflicting hypotheses. An alternative explanation for the distinct composition of the Avalon-type assemblage is that it was a terrestrial assemblage of volcaniclastic coastal soils near a continental volcanic arc []. This view is based on geochemical studies of the substrates of Mistaken Point fossils and associated matrix supported tuffs and volcanic bombs that could only form on land [].

Some of these fossils such as Fractofusus and Charniodiscus were found in red well drained paleosols of coastal plains, but others such as Aspidella were found in pyritic intertidal paleosols. The Ediacara-type assemblage is named after Australia's Ediacara Hills , and consists of fossils preserved in facies of coastal lagoons and rivers. They are typically found in red gypsiferous and calcareous paleosols formed on loess and flood deposits in an arid cool temperate paleoclimate.

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 fossils represent burrowing organisms, [47] while Guy Narbonne maintains they were surface dwellers. The environment is interpreted as sand bars formed at the mouth of a delta 's distributaries.

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.

An analysis of one of the White Sea fossil beds, where the layers cycle from continental seabed to inter-tidal to estuarine and back again a few times, found that a specific set of Ediacaran organisms was associated with each environment.

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. Just four are represented in the Avalon assemblage. From Wikipedia, the free encyclopedia. Redirected from Ediacara biota. Enigmatic tubular and frond-shaped, mostly sessile organisms that lived during the Ediacaran Period ca.

For other uses, see Ediacara. The Ediacara biota in context. We are offering simple typing job with good p Hi Guys, we are a new and growing Classified Ads website. Buy, Sell or swap almost anything with BizzyAds. Post Your Ad Login. Swap - Excha 0. Make Money Posting Hello there, Work in the comfort of home p Technical Support fo Web applications are becoming ever more widel

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