The Garden of Ediacara

McMenamin, Mark A. S.

doi:10.2307/3514512

Cited by 85 publications

(46 citation statements)

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“…Olenids were derived from benthic, particle-feeding ancestors, exhibiting progressive morphological specializations that are suggestive of obligate adaptations to the dysaerobic environment of the olenid sea. Other forms of symbiosis may be much older, if the claims of Ediacaran animals as examples of photosynthetic symbionts are to be credited (36). However, the environmental indicators of the olenid habitat, and the constraints on the lifestyle of these undoubted arthropods, are more critically constrained than is the case with the late Precambrian enigmatic metazoans.…”

Section: Discussionmentioning

confidence: 99%

Olenid trilobites: The oldest known chemoautotrophic symbionts?

Fortey

2000

Proc. Natl. Acad. Sci. U.S.A.

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Late Cambrian to early Ordovician trilobites, the family Olenidae, were tolerant of oxygen-poor, sulfur-rich sea floor conditions, and a case is made that they were chemoautotrophic symbionts. Olenids were uniquely adapted to this habitat in the Lower Paleozoic, which was widespread in the Late Cambrian over Scandinavia. This life habit explains distinctive aspects of olenid morphology: wide thoraces and large numbers of thoracic segments, thin cuticle and, in some species, degenerate hypostome, and the occasional development of brood pouches. Geochemical and field evidence is consistent with this interpretation. Olenids occupied their specialized habitat for 60 million years until their extinction at the end of the Ordovician.

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Section: Discussionmentioning

confidence: 99%

Olenid trilobites: The oldest known chemoautotrophic symbionts?

Fortey

2000

Proc. Natl. Acad. Sci. U.S.A.

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“…Ediacarans lack a head, digestive system, muscle, and other tissue. They display features that, taken together, suggest they were not animals (McMenamin, 1998). Accordingly, they are the Ediacara biota, not fauna.…”

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confidence: 94%

“…They have been extinct since the early Cambrian, and are found preserved in sandstone. Large extant protoctists (e.g., cellular slime molds, kelp, and calcified red algae) and most Ediacarans display a peculiar form of multicellularity (termed "metacellularity" by McMenamin, 1998). Ediacarans lack a head, digestive system, muscle, and other tissue.…”

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confidence: 99%

Motility proteins and the origin of the nucleus

et al. 2002

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Hypotheses on the origin of eukaryotic cells must account for the origin of the microtubular cytoskeletal structures (including the mitotic spindle, undulipodium/cilium (so-called flagellum) and other structures underlain by the 9(2)ϩ2 microtubular axoneme) in addition to the membrane-bounded nucleus. Whereas bacteria with membrane-bounded nucleoids have been described, no precedent for mitotic, cytoskeletal, or axonemal microtubular structures are known in prokaryotes. Molecular phylogenetic analyses indicate that the cells of the earliest-branching lineages of eukaryotes contain the karyomastigont cytoskeletal system. These protist cells divide via an extranuclear spindle and a persistent nuclear membrane. We suggest that this association between the centriole/kinetosome axoneme (undulipodium) and the nucleus existed from the earliest stage of eukaryotic cell evolution. We interpret the karyomastigont to be a legacy of the symbiosis between thermoacidophilic archaebacteria and motile eubacteria from which the first eukaryote evolved. Mutually inconsistent hypotheses for the origin of the nucleus are reviewed and sequenced proteins of cell motility are discussed because of their potential value in resolving this problem. A correlation of fossil evidence with modern cell and microbiological studies leads us to the karyomastigont theory of the origin of the nucleus. Anat Rec 268: 290 -301, 2002.

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“…In fact, if the Vendobiontan hypothesis (Seilacher, 1989(Seilacher, , 1992) is correct, the largest mass extinction in history separates the Vendian and Cambrian, at least in terms of the rank of the taxa that it claimed; no other mass extinction, as far as we know, has destroyed an entire kingdom. Any number of scenarios can be devised for said extinction, from vulcanism or bolide impact (Felitsyn et al, 1989) the evolution of predators (McMenamin, 1986;Seilacher, 1989). However, if the Vendian organisms were early representatives of several extant taxa, then the presumed extinction event loses magnitude: perhaps the difference between Vendian and Cambrian biotas is due more to rapid diversification and pseudoextinction, possibly coupled with changes in taphonomic conditions, than to mass extinction in the usual sense.…”

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confidence: 99%

Phylogenetic Hypotheses of the Relationships of Arthropods to Precambrian and Cambrian Problematic Fossil Taxa

Waggoner¹

1996

Systematic Biology

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Abstract.-A number of Vendian (latest Precambrian) body fossils have traditionally been considered arthropods or arthropodlike organisms. Several Cambrian "weird wonders" have also been linked with the arthropods. However, these relationships are difficult to express in traditional Linnean systematics. I present a morphological cladistic analysis of seven Vendian "arthropodlike" taxa compared with 21 representative Cambrian arthropods, lobopods, and weird wonders. Four arthropods from the later Phanerozoic (a pycnogonid, a monuran, and the problematic Chebnielbn and Arthropleura), five extant tardigrades, two extant kinorhynchs, and an extant priapulid, myriapod, pycnogonid, and onychophoran are also included. Monophyly of the Arthropoda is supported, but the anomalocarids and their relatives (Anomalopoda) fall out very close to the base of the traditional Arthropoda and should be included within it. The relationships among arthropods with uniramous appendages are not well resolved, but the group does not appear to be monophyletic. The biramous arthropods do form a clade and are divided into a crustaceanomorph clade and an arachnomorph clade that includes the trilobites. Most Vendian arthropodlike fossils form two clades, the Vendiamorpha and the Sprigginidae, in the arthropod stem group. The Lobopoda is a monophyletic clade with three branches: tardigrades, onychophorans, and marine lobopods. An unranked taxonomic scheme is proposed for the major clades identified here. There is no compelling reason to accept the hypothesis that the Vendian organisms included here are not metazoans. [Precambrian; Vendian; Ediacara fauna; Cambrian; problematica; arthropod; lobopod.] There is something about writing about arthropod phylogeny that brings out the worst in people.-J. W. Hedgpeth (Schram, 1981) The soft-bodied megafossils of the Vendian or Ediacaran (late Precambrian or Neoproterozoic) have classically been considered metazoans in extant phyla, often in or near extant classes or orders (e.g., Glaessner, 1984). However, a number of dissenting opinions place most or all of these fossils in an extinct kingdom Vendobionta (Seilacher, 1989(Seilacher, , 1992Bergstrom, 1991), an extinct metazoan phylum (Buss and Seilacher, 1994), or an extant nonmetazoan kingdom (e.g., Zhuravlev, 1993;Retallack, 1994), thereby denying them any direct significance for early metazoan evolution. Obstacles to considering the "Vendobionta" as early metazoans include the time gap between the disappearance of Vendian biotas and the appearances of Cambrian faunas, the lack of Vendian-type soft-bodied organisms in the Cambrian and later Lagerstatten; and supposed morphological disparity between most Vendian organisms and their Phanerozoic successors.Resolution of this debate would be desirable, because our understanding and interpretation of the Precambrian-Cambrian transition is colored by our taxonomic pronouncements. The magnitude of whatever extinction took place between the Vendian and Cambrian is an example of this. If the Vendian organisms...

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The Garden of Ediacara

Cited by 85 publications

References 0 publications

Olenid trilobites: The oldest known chemoautotrophic symbionts?

Olenid trilobites: The oldest known chemoautotrophic symbionts?

Motility proteins and the origin of the nucleus

Phylogenetic Hypotheses of the Relationships of Arthropods to Precambrian and Cambrian Problematic Fossil Taxa

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