There is no such thing as the ‘Ediacara Biota’

MacGabhann, Breandán Anraoi

doi:10.1016/j.gsf.2013.08.001

Cited by 30 publications

(24 citation statements)

References 88 publications

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“…This is especially true in the Neoproterozoic, with numerous extinct lineages existing alongside the ancestors of extant discoidal organisms. In addition, structural elements within the water column, including more delicate frondose structures, are far more difficult to preserve than body parts within or on the substrate [51,103,104]. As a result, it may be impossible to identify whether or not discoidal structures are holdfasts of epibenthic frondose organisms.…”

Section: Discussionmentioning

confidence: 99%

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Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway

Kirkland

MacGabhann

Kirkland³

et al. 2016

PLoS ONE

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The Hellefjord Schist, a volcaniclastic psammite-pelite formation in the Caledonides of Arctic Norway contains discoidal impressions and apparent tube casts that share morphological and taphonomic similarities to Neoproterozoic stem-holdfast forms. U-Pb zircon geochronology on the host metasediment indicates it was deposited between 437 ± 2 and 439 ± 3 Ma, but also indicates that an inferred basal conglomerate to this formation must be part of an older stratigraphic element, as it is cross-cut by a 546 ± 4 Ma pegmatite. These results confirm that the Hellefjord Schist is separated from underlying older Proterozoic rocks by a thrust. It has previously been argued that the Cambrian Substrate Revolution destroyed the ecological niches that the Neoproterozoic frond-holdfasts organisms occupied. However, the discovery of these fossils in Silurian rocks demonstrates that the environment and substrate must have been similar enough to Neoproterozoic settings that frond-holdfast bodyplans were still ecologically viable some hundred million years later.

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Section: Discussionmentioning

confidence: 99%

“…The preservation of imprints or traces from soft-bodies necessitates a general lack of heavy bioturbation [92]. As in the case of many Ediacaran sites, certain body elements may not have been preserved due to removal in the water column or labile tissue destruction prior to complete lithification [104]. …”

Section: Discussionmentioning

confidence: 99%

Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway

Kirkland

MacGabhann

Kirkland³

et al. 2016

PLoS ONE

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“…Before the modern dating era it was widely considered that the Ediacaran biota considerably pre‐dated the Cambrian (Laflamme et al , ; MacGabhann, ), and even after redating placed the two biotas in close temporal proximity, there has been a tendency to regard them as being separated by a mass extinction (e.g. Amthor et al , ; Narbonne, ; Darroch et al , ).…”

Section: The Fate Of the Ediacarans And The Rise Of The Bilateriansmentioning

confidence: 99%

The origin of the animals and a ‘Savannah’ hypothesis for early bilaterian evolution

2015

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The earliest evolution of the animals remains a taxing biological problem, as all extant clades are highly derived and the fossil record is not usually considered to be helpful. The rise of the bilaterian animals recorded in the fossil record, commonly known as the 'Cambrian explosion', is one of the most significant moments in evolutionary history, and was an event that transformed first marine and then terrestrial environments. We review the phylogeny of early animals and other opisthokonts, and the affinities of the earliest large complex fossils, the so-called 'Ediacaran' taxa. We conclude, based on a variety of lines of evidence, that their affinities most likely lie in various stem groups to large metazoan groupings; a new grouping, the Apoikozoa, is erected to encompass Metazoa and Choanoflagellata. The earliest reasonable fossil evidence for total-group bilaterians comes from undisputed complex trace fossils that are younger than about 560 Ma, and these diversify greatly as the Ediacaran-Cambrian boundary is crossed a few million years later. It is generally considered that as the bilaterians diversified after this time, their burrowing behaviour destroyed the cyanobacterial mat-dominated substrates that the enigmatic Ediacaran taxa were associated with, the so-called 'Cambrian substrate revolution', leading to the loss of almost all Ediacara-aspect diversity in the Cambrian. Why, though, did the energetically expensive and functionally complex burrowing mode of life so typical of later bilaterians arise? Here we propose a much more positive relationship between late-Ediacaran ecologies and the rise of the bilaterians, with the largely static Ediacaran taxa acting as points of concentration of organic matter both above and below the sediment surface. The breaking of the uniformity of organic carbon availability would have signalled a decisive shift away from the essentially static and monotonous earlier Ediacaran world into the dynamic and burrowing world of the Cambrian. The Ediacaran biota thus played an enabling role in bilaterian evolution similar to that proposed for the Savannah environment for human evolution and bipedality. Rather than being obliterated by the rise of the bilaterians, the subtle remnants of Ediacara-style taxa within the Cambrian suggest that they remained significant components of Phanerozoic communities, even though at some point their enabling role for bilaterian evolution was presumably taken over by bilaterians or other metazoans. Bilaterian evolution was thus an essentially benthic event that only later impacted the planktonic environment and the style of organic export to the sea floor.

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“…To avoid future confusion and unhelpful generalisations, careful and consistent application of terminology across the field, and an agreed taxonomic framework for the description of Ediacaran taxa, are now required (cf. Brasier et al, 2012;MacGabhann, 2014).…”

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confidence: 99%

Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota

2015

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Ediacaran macrofossils from the Avalon Terrane (primarily eastern Newfoundland and the central U.K.) record some of the earliest large and complex multicellular organisms on Earth.Perhaps the greatest unknown regarding these fossils is their relevance to the early evolutionary history of the Kingdom Animalia. In recent years, new data and discoveries have revealed insights into Ediacaran paleobiology, taxonomic relationships, paleoecology and taphonomy, significantly refining our understanding of Avalonian ecosystems. Here, we summarise recent observational and quantitative studies, and their bearing on the current understanding of Avalonian benthic marine ecosystems. A review of existing knowledge of the biological composition of Avalonian marine assemblages demonstrates that they recorddensely-populated ecosystems inhabited by a diverse range of organisms, likely representing multiple biological Kingdoms. Appreciation of this diversity, and of the complexities it introduces to paleoecological studies, is vital when considering the relationship between macroevolution and contemporaneous climatic, tectonic and geochemical events. We then summarise current understanding of Avalonian paleoecology. Studies into locomotion, reproduction, feeding strategies, and community structure and succession reveal that these ecosystems were considerably different to Phanerozoic settings. Furthermore, we suggest that Avalonian ecosystems witnessed the appearance of novel nutrient sources, offering new opportunities and niches for benthic organisms. The suggestion that the numerically dominant rangeomorphs were osmotrophic is reviewed and appraised in light of geochemical, morphological, and biological information. Finally, the use of modern ecological metrics in the study of Ediacaran fossil assemblages is assessed. Concerns regarding the interpretation of paleoecological data are outlined in light of current taphonomic and sedimentological understanding, and these cast doubt on previous suggestions that the Avalonian assemblages were largely composed of metazoans. Nevertheless, we emphasise that if treated with necessary caution, paleoecological data can play a significant role in assisting efforts to determine the biological affinities of late Ediacaran macroscopic organisms.

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There is no such thing as the ‘Ediacara Biota’

Cited by 30 publications

References 88 publications

Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway

Cryptic Disc Structures Resembling Ediacaran Discoidal Fossils from the Lower Silurian Hellefjord Schist, Arctic Norway

The origin of the animals and a ‘Savannah’ hypothesis for early bilaterian evolution

Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota

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