Ediacaran biota

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Smith609 (talk | contribs) at 22:07, 8 April 2007. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

The Ediacaran Biota represent the earliest known multicellular fossils. Their unusual morphology has made classification of many representatives difficult; indeed opinion is still divided on which kingdom some species belong to! Whilst the first Ediacaran fossils were discovered in 1946, their full significance was not identified until their re-examination in 1984. The biota appear to have diversified with time until the Early Cambrian, when competition gradually reduced their diversity and abundance. No recognisable Ediacaran-style fossils have been recognised after the Burgess Shale during the Mid-Cambrian.

{{:Ediacaran_biota/Timeline}}


History

Discoveries

Namibia

Charnwood

In 1946, Reg Sprigg noticed 'jellyfish' in the Ediacaran Hills of Australia's Flinders Ranges. [1] At this time, the rocks were dated as Early Cambrian, and the reports did not receive much attention[2] until ten years later, when amateur collection and improved stratigraphic dating made it clear that the Ediacaran fauna provided evidence for the first pre-Cambrian multicellular animals.


Mistaken Point

Early Interpretations

Cnidarians

A sea-pen, bearing passing resemblance to Charnia

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[3]. The fossils of the Ediacara Hills could be comfortably accommodated in these groups, resulting in the coining of the term 'Ediacaran fauna'.

'The dawn of animal life'

Martin Glaessner believed the Ediacaran biota to represent early stem group members of all modern phyla, representing forms we don't recognise since they had yet to evolve the characteristic features we use in modern classification.[4]

New Phylum

Dolf Seilacher most famously suggested that the Ediacaran organisms represented a unique and extinct grouping (clade) and created the phylum Vendozoa[5][6] which he later renamed (to 'Vendobionta') and refined to exclude fossils identified as animals. He described the Vendibionta as quilted cnidarians lacking stinging cells (cnidæ), . The lack of cnidæ would prevent them feeding in their present manner, and Seilacher suggested that the organisms may have survived by symbiosis with photosynthetic or chemoautotrophic organisms,[7] a mode of life that has since been popularly accepted.

Lichens

Gregory Retallack's hypothesis that Ediacaran organisms were lichens[8] failed to gain wide-spread acceptance. He argues that the fossils are not squashed as much as other examples of jellyfish fossilised in similar situations, and their relief is more similar to that of wood. The chitinous walls of lichen colonies would provide a similar resistance to compaction. The organisms' large size - sometime over a metre across, far larger than any preserved burrows - is also used to suggest that they are not animals.

Other interpretations

Almost every possibly group has been put forward as a candidate to accommodate the Ediacaran Biota[9], from Algæ[10], to protists known as foramanifera,[11] to fungi[12] to bacterial or microbial colonies[13], to hypothetical intermediates between plants and animals.[14] Since representatives of almost all modern groups of organisms (phyla) were in existence by the mid-Cambrian, it seems probable that precursors to many phyla would be represented in the Ediacaran: attempts to group them into one phylum would then be doomed to failure.


Morphology

A vast range of morphological characteristics are encompassed by the Ediacaran biota. Size varies from centimeter to meter scale; complexity from 'blob-like' to intricate. Symmetry forms include radial, bilateral, trigonal, tetragonal and pentameral; rigidity ranges from sturdy and resistant to jelly-soft.[15]

Trace Fossils

The only trace fossils preserved are horizontal, on the then-surfaces. These traces imply the presence of motile, probably bilateral, organisms with heads. It would be highly surprising if these weren't animals.[16]

Discs

Cyclomedusa, a disc shaped fossil that has been interpreted as a microbial artefact

Circular fossils, such as Ediacaria and Cyclomedusa, were the main cause of early recognition of fossils as jellyfish. However, further examination has provided alternative interpretations of all existing disc-shaped fossils; a combination of factors have meant that none are now confidently recognised as jellyfish!

Identifications include holdfasts and anemomes; since only the undersides of fossils are preserved diagnostic characters are often lacking!

Quilted organisms

File:Dickinsonia costata.png
Dickinsonia costata, an organism with quilted appearance

The organisms considered in Seilacher's revised definition of the Vendobionta[17] have in common a 'quilted' appearance resembling an inflatable mattress. These quilts were sometimes torn or ruptured during the preservational process, and such damages specemins provide valuable clues in the reconstruction process. For example, Swartpuntia Germsi was only recognised as having three (or more) petaloid fronds after the description of a posthumously damaged specimen.[18] It is this class of organism, containing the famous Charnia and Charniodiscus, that most captures the imagination, and that has proven the most difficult to position into the existing tree of life; indeed there is debate over whether the quilted structure is shared only by all members of a clade (i.e. is synapomorphic), or whether it evolved multiple times (pleisiomorphy).

Kimberella

The organism Kimberella does not fit into any of the above categories and is currently interpreted as a bilaterian possessing a sturdy but unmineralised shell.[19]

Origin and fate

Appearance

It is a matter of debate as to whether the appearance of multicellular life around 575 million years ago requires any special explanation, or whether the slow process evolution simply required almost 4 billion years to accumulate the necessary machinery.

The main limiting factor to large life forms was atmospheric oxygen concentration, which could not accumulate until photosynthesising organisms had produced enough to 'rust the planet' and oxidise all the free iron and other reducing agents. Donald Canfield detected the first accumulation of oxygen, albeit to only a percent of current levels, around the same time as the first Ediacaran fossils appeared.[20] The presence of atmospheric oxygen has thus been heralded as a possible 'trigger' for the Ediacaran radiation.[21]

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.[22]

Disappearance

Preservation

The sudden disappearance of Ediacaran fossils around the start of the Cambrian could be due simply to conditions no longer favouring the fossilisation of Ediacaran organisms, which may have continued to thrive unpreserved.[23] However, were they common, it would be expected that more than the occasional specimen[24] would be found in Lagerstätten such as the Burgess Shale - unless such assemblages represent an environment never occupied by the Ediacaran biota.

Higher trophic levels - predation and grazing

Microbial mats largely disappear in the Early Cambrian due to pressure from grazers. The introduction of organisms with a grazing way of life contemporaneous to the decline of the Ediacaran biota may suggest that the grazers fed directly on the Ediacaran biota, that they destabilised the microbial substrate, leading to displacement or detachment of the biota, or that the destruction of the mat destabilised the ecosystem.

Alternatively skeletal 'predators' (assuming that the Ediacaran biota could be termed 'prey') could have fed directly on the relatively undefended Ediacaran biota.[25] However, the existence of the recognised predator Kimberella suggests that the biota had already had limited exposure to predation.

Competition

It is possible that increased competition due to the evolution of key innovations amongst other groups, perhaps as a response to predation[26], drove the Ediacaran biota from their niches. However, attempts to use this argument to explain similar phenomena have not withstood in-depth analysis. Drawing an example from the shellfish, the bivalve molluscs' 'competitive exclusion' of brachiopods was eventually deemed to be a coincidence of two unrelated trends.[27]

Change in environmental conditions

Whilst it is difficult to infer the effect of changing planetary conditions on organisms, communities and ecosystems, the time around the terminal Precambrian and Early Cambrian was one of huge change. The breakup of supercontinents,[28] rising sea levels (creating shallow, 'life-friendly' seas),[29] fluctuations in atmospheric composition, including oxygen and carbon dioxide levels,[30] and changes in ocean chemistry[31] (promoting biomineralisation)[32] could all have played a part in transforming the shape of early life.


Assemblages

{{:Ediacaran_biota/Sub-biota_Timeline}} Ediacaran-type fossils are recognised worldwide in a variety of depositional conditions, and are commonly grouped into three main types, named Avalon-type, Ediacara-type and Nama-type after typical localities.

Preservation

The soft-bodied nature of the Ediacaran biota makes their abundant preservation surprising. It is undoubtedly helped by the absence of vertically burrowing infaunal creatures[33], which disturbed the sediment (disturbing soft-bodied impressions before they could fossilise) once they evolved in the Cambrian.

Sedimentary environment

The fossils were preserved by virtue of rapid covering by ash or sand, trapping their mould against the muddy or microbial substrate on which they lived.[34] As ash is readily dated to a high degree of accuracy, fossils found under ash beds can be designated ages accurate to the nearest million years or better.[35] However, it is more common to find Ediacaran fossils under sandy beds deposited in storms or during a turbidite event (an offshore high-discharge 'flood'),[36]. Soft-bodied organisms today almost never fossilise under such events. It is likely that the presence of widespread microbial mats, which ceased to exist due to the evolution of grazing organisms[citation needed], aided preservation by stabilising the sediment below.[37] Very few Ediacaran age strata with the 'elephant skin' texture signifying a microbial mat are devoid of fossils, and Ediacaran fossils are almost never found in beds not containing microbial mats.

What is preserved?

Whether the top or bottom of an organism is preserved is dependant on the rate of cementation of the overlying substrate, relative to the rate of decomposition of the organism.

Most disc-shaped fossils decomposed before the overlying sediment was cemented - hence the ash or sands slumped in to fill the void, only allowing the preservation 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 simply abrading or destroying the organism as it would the less-resistant discs.

Ediacara-type assemblage

[[Image:Ediacara_assemblage...thumb|Reconstruction of an Ediacara-type assemblage, defined by the presence of Dickinsoniids, Trilobozoans, Eoporpita, Praœopascichnids, Kimberella and Charniodiscus..[38]]] The Ediacara-type assemblage consists of fossils preserved in prodeltaic facies - that is, 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.[39]

Avalon-type assemblage

[[Image:Avalon_assemblage...thumb|Reconstruction of an Avalon-type assemblage, defined by the presence of Charnia, Bradgatia and Khatyspytia.[40]]] The Avalon-type assemblage is defined by its type locality Mistaken point, the oldest locality bearing a large quantity of Ediacaran fossils.[41] The assemblage is easily dated as it contains many fine ash-beds, which are a good source of the zircons used in the uranium-lead method of radiometric dating. These fine-grained ash beds can also preserve exquisite detail.


The biota comprises deep sea dwelling organisms,[42] probably preserved in situ (without post-mortem transportation), although this point is not universally accepted. The assemblage, whilst less diverse than the Ediacara- or Nama-types, is said to resemble Carboniferous filter-feeding communities, which may suggest a filter feeding way of life - most interpretations place the water depth as too deep to allow photosynthesis. The low diversity may reflect the depth of water - which would restrict speciation opportunities - or the early age of the assemblage, with not enough time having passed for evolution to produce a rich biota. Opinion is currently divided between the conflicting hypotheses.Cite error: A <ref> tag is missing the closing </ref> (see the help page).]] The Nama assemblage is best represented in Nama, Namibia. 3D preservation is most common, with organisms being preserved in sandy beds containing internal bedding. Dima Grazhdankinbelieves that these organisms represent infaunal burrowing organisms,[43] whilst Guy Narbonne maintains that they were epifaunal surface dwellers.[citation needed] These interesting beds are sandwiched between units comprising interbedded sandstones, siltstones and shales, with microbial mats, where present, usually containing fossils. The environment is interpreted as being sand bars at the mouths of distributaries of deltas.[44]

Significance of assemblages

The three different types of assemblage have all been found in the White Sea region of Russia, and there is some doubt as to the meaning of the assemblages.

The large overlap in time of the faunas makes it unlikely that they represent evolutionary stages or temporally distinct communities.

Since they are globally distributed - described on all continents but Antarctica - geographical boundaries do not appear to have had any effect[45]; the same fossils are found at all palæolatitudes and in distinct sedimentary basins[46].

It is most likely that the three assemblages mark organisms adapted to survival in different facies (environments), and that any apparent patterns in diversity or age are in fact an artefact of our limited sampling - the timeline, left, demonstrates the paucity of Ediacaran fossil-bearing assemblages.



Significance

-

Lifestyle & Ecology

The Ediacaran biota represents an early stage in the history of multicellular life, and as such it is perhaps not surprising that not all possible modes of life are occupied. In a popular recent article, Bambach et al estimate that of the 92 potentially possible modes of life, no more than a dozen are occupied by the end of the Ediacaran - just four are represented in the Avalon assemblage.[47] The lack of large-scale predation and vertical burrowing are perhaps the most significant factors limiting the ecological diversity; the appearance of these during the Early Cambrian allowed the number of lifestyles occupied to rise to thirty.

-

Dating

-

Affinities

McMenamin concludes that although they were related to animals, Ediacarans were not animals in the strict sense, because they never passed through an embryonic stage, which is peculiar to known animal life forms. But they seem to have developed a central nervous system and brains independent from animal evolution. This finding has profound ramifications for our understanding of evolutionary biology, for it indicates that the path toward intelligent life was embarked upon more than once on this planet.[48]


Further reading

List of Ediacaran biota

-

-

-

References

  1. ^ Sprigg, R.C. (1947). "Early Cambrian "jellyfishes" of Ediacara, South Australia and Mount John, Kimberly District, Western Australia". Transactions of the Royal Society of South Australia. 73: 72–99. {{cite journal}}: |access-date= requires |url= (help); C1 control character in |title= at position 29 (help); Check date values in: |accessdate= (help)
  2. ^ Sprigg, R.C. (1991). "Martin E Glaessner: Palaeontologist extraordinaire". Mem. Geol. Soc. India. 20: 13–20. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); line feed character in |title= at position 36 (help)
  3. ^ Donovan, Stephen K., Lewis, David N. (2001). "Fossils explained 35. The Ediacaran biota". Geology Today. 17 (3): 115–120. doi:10.1046/j.0266-6979.2001.00285.x. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)CS1 maint: multiple names: authors list (link)
  4. ^ Glaessner, M.F. (1984). The Dawn of Animal Life: A Biohistorical Study. Cambridge University Press.
  5. ^ Seilacher, A. (1984). "Late Precambrian and Early Cambrian Metazoa: preservational or real extinctions". Patterns of Change in Earth Evolution: 159–168. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  6. ^ Seilacher, A. (1989). "Vendozoa: organismic construction in the Proterozoic biosphere". Lethaia. 17: 229–239. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  7. ^ Buss, L.W. and Seilacher, A. (1994). "The Phylum Vendobionta: A Sister Group of the Eumetazoa?". Paleobiology. 20 (1): 1–4. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)CS1 maint: multiple names: authors list (link)
  8. ^ Retallack, G.J. (1994). "Were the Ediacaran fossils lichens". Paleobiology. 17: 523–544. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  9. ^ Waggoner, Ben (1998). [intl-icb.oxfordjournals.org "Interpreting the Earliest Metazoan Fossils: What Can We Learn?"]. Integrative and Comparative Biology. Retrieved 8th March 2007. {{cite journal}}: Check |url= value (help); Check date values in: |accessdate= (help)
  10. ^ Ford, T.D. (1958). "Pre-Cambrian fossils from Charnwood Forest". Proceedings of the Yorkshire Geological Society. 31: 211–217. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  11. ^ Zhuralev (1992). "Were Vend-Ediacaran multicellulars metazoa?". Abstracts of the international Geological Congress, Kyoto, Japan. 2: 339. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  12. ^ Peterson, K.J. and Waggoner, B. and Hagadorn, J.W. "A Fungal Analog for Newfoundland Ediacaran Fossils?". Integrative and Comparative Biology. 43 (1): 127–136. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)CS1 maint: multiple names: authors list (link)
  13. ^ Grazhdankin, Dima (2001). "Microbial origin of some of the Ediacaran fossils". GSA Annual Meeting, November 5-8, 2001. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  14. ^ Pflug (1973). "Zur fauna der Nama-Schichten in Südwest-Afrika. IV. Mikroscopische anatomie der petalo-organisme". Paleontographica (in German) (B144): 166–202. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  15. ^ Narbonne, Guy M. "The Ediacara Biota: A Terminal Neoproterozoic Experiment in the Evolution of Life". GSA Today. 8 (2): 1–6. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  16. ^ Fedonkin, M.A. (1992). "Vendian faunas and the early evolution of Metazoa". in Lipps, J., and Signor, P. W., eds., Origin and early evolution of the Metazoa: New York, Plenum Press.: 87–129. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); line feed character in |journal= at position 33 (help), , , , p. .
  17. ^ Seilacher, A. (1992). "Vendobionta and Psammocorallia: lost constructions of Precambrian evolution". Journal of the Geological Society, London. 149: 607–613. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  18. ^ Narbonne, G.M. (1997). "The Youngest Ediacaran Fossils from Southern Africa". Journal of Paleontology. 71 (6): 953–967. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  19. ^ Fedonkin, M.A. (1997). "The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism". Nature. 388: 868–871. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ Canfield, D. E., and Teske, A., Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies. Nature 382:127–132.
  21. ^ {{cite d2007lnd, title=Template:Late-Neoproterozoic Deep-Ocean Oxygenation and the Rise of Animal Life, author={Canfield, D.E. and Poulton, S.W. and Narbonne, G.M.}, journal={Science}, volume={315}, number={5808}, pages={92}, year={2007} }}
  22. ^ Narbonne, Guy M. (2003). "Life after Snowball: The Mistaken Point biota and the origin of animal ecosystems". Seattle Annual Meeting. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help)
  23. ^ Runnegar, B.N. (1992). "Proterozoic metazoan body fossils". The Proterozoic Biosphere, a Multidisciplinary Study: Cambridge University Press, New York: 369--387. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  24. ^ Conway Morris, S. (1993). "Ediacaran-like fossils in Cambrian Burgess Shale–type faunas of North Americ". Palaeontology. 36: 593–635. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); line feed character in |title= at position 26 (help)
  25. ^ McMenamin M. (1986). The Garden of Ediacara. {{cite book}}: |access-date= requires |url= (help); |journal= ignored (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help)
  26. ^ Stanley, S.M. (1973). "An ecological theory for the sudden origin of multicellular life in the Late Precambrian". Proc. Nat. Acad. Sci. U.S.A. 72: 646–650. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help)
  27. ^ Gould, S.J. (1980). "Clams and Brachiopods-Ships that Pass in the Night". Paleobiology. 6 (4): 383–396. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  28. ^ McKerrow, W.S. (1992). "Early Cambrian continental reconstructions". Journal of the Geological Society, London. 149: 599–606. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  29. ^ Hallam, A. (1984). "Pre-Quarernary sea-level changes". Ann. Rev. 12: 205–243. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help)
  30. ^ Brasier, M.D. (1992). "Global ocean-atmosphere change across the Precambrian-Cambrian transition". Geological Magazine. 129 (2): 161–168. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help)
  31. ^ Lowenstein, T.K. (2001). "Oscillations in Phanerozoic Seawater Chemistry: Evidence from Fluid Inclusions". {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite journal requires |journal= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  32. ^ Bartley, J.K. (1998). "A Vendian--Cambrian boundary succession from the northwestern margin of the Siberian Platform: stratigraphy, palaeontology, chemostratigraphy and correlation". Geological Magazine. 135 (4): 473–494. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  33. ^ Stanley, S.M. (1973). "An ecological theory for the sudden origin of multicellular life in the Late Precambrian". Proc. Nat. Acad. Sci. U.S.A. 72: 646–650. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help) (This reference is a duplicate of 26 but I can't work out how to link it as such.)
  34. ^ Narbonne, Guy M. (1998). "The Ediacara biota: A terminal Neoproterozoic experiment in the evolution of life" (PDF). GSA. 8 (2): 1–6. Retrieved 8th March 2007. {{cite journal}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help) This ref also cited multiple times - please remove repetition if you can!
  35. ^ Bowring, S.A. (2001). "Calibration of the Fossil Record". Palæobiology II, Briggs & Crowther eds; Blackwell publishing group. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help), S. A. and M. W. Martin, in , 2001
  36. ^ Narbonne 1998
  37. ^ Gehling, J.G. (1987). "Earliest known echinoderm— A new Ediacaran fossil from the Pound Subgroup of South Australia". Alcheringa. 11: 337–345. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); line feed character in |title= at position 27 (help)
  38. ^ Grazhdankin 2004
  39. ^ Template:Cite journal id=Grazhdankin2004
  40. ^ Template:Cite journal id=Grazhdankin2004
  41. ^ Benus in Landing, E., Narbonne, G. M., and Myrow, P., editors, 1988, Trace fossils, small shelly fossils and the Precambrian- Cambrian boundary: New York State Museum Bulletin 463, 81 p.
  42. ^ Paleobiology, 29(4), 2003, pp. 527–544 Paleoecology of the oldest known animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland Matthew E. Clapham, Guy M. Narbonne, and James G. Gehling
  43. ^ Dima Grazhdankin and Adolf Seilacher. 2002. Underground Vendobionta from Namibia. Palaeontology 45:57–78.
  44. ^ Template:Cite journal id=Grazhdankin2004
  45. ^ @article{waggoner1999bae, title=Template:Biogeographic Analyses of the Ediacara Biota: A Conflict with Paleotectonic Reconstructions, author={Waggoner, B.}, journal={Paleobiology}, volume={25}, number={4}, pages={440--458}, year={1999}, publisher={JSTOR} }
  46. ^ Template:Cite id=Grazhdankin2004
  47. ^ {{Cite title=Template:AUTECOLOGY AND THE FILLING OF ECOSPACE: KEY METAZOAN RADIATIONS, | author={BAMBACH, R.K. and BUSH, A.M. and ERWIN, D.H.}, | journal={complexity}, | volume=50(1), | pages={1-22}, | year=2007 | url=http:www.blackwell-synergy.com/doi/full/10.1111/j.1475-4983.2006.00611.x | publisher=Blackwell Synergy }}
  48. ^ @book{macmenamin1998ged, title=Template:The Garden of Ediacara: discovering the first complex life, author={MacMenamin, M.A.S. and McMenamin, M.}, year={1998}, publisher={Columbia University Press} }

[[Category:Geology]] [[Category:Paleontology]] [[Category:Ediacaran biota]]

Retrieved from "https://en.wikipedia.org/w/index.php?title=Ediacaran_biota&oldid=121276574"