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Reconstructing Rangea: new discoveries from the Ediacaran of southern Namibia
- Patricia Vickers-Rich, Andrey Yu. Ivantsov, Peter W. Trusler, Guy M. Narbonne, Mike Hall, Sasha Wilson, Carolyn Greentree, Mikhail A. Fedonkin, David A. Elliott, Karl H. Hoffmann, Gabi I. C. Schneider
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- Journal:
- Journal of Paleontology / Volume 87 / Issue 1 / January 2013
- Published online by Cambridge University Press:
- 20 May 2016, pp. 1-15
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Rangea is the type genus of the Rangeomorpha, an extinct clade near the base of the evolutionary tree of large, complex organisms which prospered during the late Neoproterozoic. It represents an iconic Ediacaran taxon, but the relatively few specimens previously known significantly hindered an accurate reconstruction. Discovery of more than 100 specimens of Rangea in two gutter casts recovered from Farm Aar in southern Namibia significantly expands this data set, and the well preserved internal and external features on these specimens permit new interpretations of Rangea morphology and lifestyle. Internal structures of Rangea consist of a hexaradial axial bulb that passes into an axial stalk extending the length of the fossil. The axial bulb is typically filled with sediment, which becomes increasingly loosely packed and porous distally, with the end of the stalk typically preserved as an empty, cylindrical cone. This length of the axial structure forms the structural foundation for six vanes arranged radially around the axis, with each vane consisting of a bilaminar sheet composed of a repetitive pattern of elements exhibiting at least three orders of self-similar branching. Rangea was probably an epibenthic frond that rested upright on the sea bottom, and all known fossil specimens were transported prior to their final burial in storm deposits.
23 - Described Taxa of Proterozoic and Selected Earliest Cambrian Carbonaceous Remains, Trace and Body Fossils
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- By Kenneth M. Towe, Smithsonian Institution, Stefan Bengtson, Uppsala Universitet, Mikhail A. Fedonkin, Palaeontological Institute, Hans J. Hofmann, University of Montreal, Carol Mankiewicz, Beloit College, Bruce N. Runnegar, University of California
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 953-1054
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Summary
Included in this Chapter are tabulations of data on which are based discussions of Proterozoic and earliest Cambrian carbonaceous remains, trace and body fossils (Chapter 7); the Late Proterozoic–Early Cambrian evolution of metaphytes and metazoans (Chapter 8); and the Proterozoic–Early Cambrian diversification of metazoans and metaphytes (Section 11.4). Specifically, tabulations (including an evaluation of the nature and origin of the taxa and objects listed) are presented below for the following six categories of megascopic remains:
(1) Proterozoic and selected Cambrian megascopic carbonaceous films (Table 23.1);
(2) described genera and species of Proterozoic and Early Cambrian calcareous algae (Tables 23.2.1–23.2.5);
(3) taxonomically described, as well as figured but not formally described, Ediacaran (Table 23.3.1) and other Proterozoic (Table 23.3.2) metazoan body fossils;
(4) taxonomically described, as well as figured but not formally described, Proterozoic (Vendian) metazoan trace fossils (Table 23.4);
(5) genera of Late Proterozoic–Early Cambrian skeletal fossils (Table 23.5); and
(6) Proterozoic and selected Cambrian megascopic dubiofossils and pseudofossils (Table 23.6).
Proterozoic and Selected Cambrian Megascopic Carbonaceous Films
In Table 23.1 are listed, alphabetically and by year of publication, reported Proterozoic and selected Cambrian megascopic films. The conventions noted below have been used in Table 23.1.
Type code: ** = holotype of the type species of the indicated genus; * = holotype of a species other than the type species of the indicated genus.
8 - The Proterozoic-Early Cambrian Evolution of Metaphytes and Metazoans
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- By Stefan Bengtson, Uppsala Universitet, Jack D. Farmer, University of California, Mikhail A. Fedonkin, Palaeontological Institute, USSR Academy of Sciences, Jere H. Lipps, University of California, Bruce N. Runnegar, University of California
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 425-462
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Summary
The fossil record of the later Proterozoic through the Early Cambrian is marked by extraordinary change. This change indicates a fundamental reorganization of the biosphere from the exclusively single-celled prokaryotic and protistan ecosystems that prevailed during much of the Proterozoic, to ecosystems characterized by complex multicellular plants and animals of the latest Proterozoic and Early Cambrian. The first recorded events in this transition took place about 900 Ma and the last about 550 Ma, a period of time exceeding that since the end of the Paleozoic. But the final and most dramatic phase, the “Cambrian Explosion,” occurred over a few tens of Ma at the onset of the Cambrian.
The glaring contrast between the Precambrian and the Phanerozoic has long been recognized as a major problem in the history of life. Darwin (1859) attempted to explain the sudden appearance of the Cambrian fauna by inadequacies of the rock record, and Walcott (1910) used a similar concept in his “Lipalian Interval” at the base of the Cambrian. Certainly the abrupt appearance in some local areas (for example, in the contact between Yudomian dolomites and Tommotian limestones in the Aldan-Lena region of Yakutia; Rozanov et al. 1969; Khomentovskij and Karlova 1986) may still be explained by incompleteness of the record.
7 - Proterozoic and Earliest Cambrian Carbonaceous Remains, Trace and Body Fossils
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- By Kenneth M. Towe, Smithsonian Institution, Stefan Bengtson, Uppsala Universitet, Mikhail A. Fedonkin, Palaeontological Institute, USSR Academy of Sciences, Hans J. Hofmann, University of Montreal, Carol Mankiewicz, Beloit College, Bruce N. Runnegar, University of California
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
-
- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 343-424
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Summary
This Chapter deals with the records of all of the Proterozoic fossil finds which are not included among the prokaryotic or protistan fossils dealt with in Chapter 5. In general, therefore, Chapter 7 deals with the earliest fossil records of higher organisms on earth. However, where systematic assignment is subject to debate there is unavoidable overlap with the prokaryotes and protists.
In historical perspective, publications describing presumed Precambrian megafossils of various kinds go back more than 100 years. Reports of carbonaceous films appeared as early as 1854 (Eichwald 1854). “Trace fossil” descriptions date from 1866 (Dawson 1866), and “body fossils” from 1872 (Billings 1872a, b). Related to the now-famous Ediacaran faunas, the first unequivocal megafossil to be described was that of Rangea schneiderhöhni reported by G. Gürich in 1930 from rocks in southwest Africa. Since these early reports, hundreds of widely, if not universally accepted Proterozoic megafossils have been described from around the world. This record of Proterozoic megafossil remains is therefore not without its share of problems which are similar to those associated with the phylogenetically lower organisms described in Chapter 5. These problems include decisions regarding biogenicity and fossil syngenicity, as well as doubts about geologic age. There are disparate taxonomic judgments, including the differing environmental and/or evolutionary interpretations such judgments may engender. In some instances the reasoning may be circular.