Nama assemblage

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Nama Assemblage
~550 – 538.8 ± 0.2 Ma [1]
Cloudina-carinata-Tamengo-Formation.png
Specimens of Cloudina carinata from the Tamengo Formation of Brazil.
Chronology

The Nama assemblage was the last of the Ediacaran biotic assemblages. Following the Avalon and White Sea assemblages, it spanned from c. 550 Ma to c. 539 Ma, coinciding with the Terminal Ediacaran biozone. [3] The assemblage was characterized by a faunal turnover, with the decline of the preexisting White Sea biota. The drop of diversity has been compared to the mass extinctions of the Phanerozoic. A second drop of diversity occurred at the Ediacaran–Cambrian boundary, concluding the Nama assemblages with the end-Ediacaran extinction. [4] [5] [6]

Contents

Etymology and definitions

The Nama assemblage is named after the Nama Group from the Tsaus Mountains of Namibia, which preserves a Late Ediacaran record of soft-bodied fossils. [3] The biota of the Namibian sites clusters with similar biotas found in the Southwestern United States, South China and British Columbia, [7] leading to a Nama assemblage being first defined by Gehling in 2001. [8] This definition of a biological assemblage usually includes the totality of the biota found in these strata, which in the case of the Nama assemblage exhibits a strong temporal element. [3]

The full division of the Ediacaran biota into three separate assemblages was first postulated by Ben Waggoner in 2003 through parsimony analysis of endemicity. This study relied on temporal, paleogeographical and paleoenvironmental data. [8] This same clustering was later recovered through hierarchical clustering and non-metric multidimensional scaling. [9] Similar methods, supplemented with a network analysis-based clustering of genera into paleocommunities, or recurrent associations of taxa, later hinted at an additional cluster (Miahoe) overlapping with the Avalon and White Sea assemblages. The Nama assemblage was also recovered and interpreted as a paleocommunity. A closely related Terminal Ediacaran biozone, contrasting with the previous Ediacaran biota biozone, was recovered when including formations in the network analysis, comprising species-poor formations mostly consisting of Nama genera. [10]

A proposed definition of the Nama assemblage as an evolutionary fauna by Wood and coauthors restricts it to new morphogroups such as calcifying metazoans, cloudinids and complex trace fossils, excluding holdovers from previous faunas such as Paracharnia . Under this definition, the assemblage's lower boundary would be the oldest appearance of Cloudina in the fossil record, placing the boundary at 550 Ma. This definition distinguishes the Nama assemblage from the Terminal Ediacaran biozone, the latter of which includes both holdovers and newer taxa. [3]

Paleohistory

During the Nama assemblage, extinction rates outpaced origination, leading to a decline in biodiversity. EdiacaranAssemblagesExtinction.svg
During the Nama assemblage, extinction rates outpaced origination, leading to a decline in biodiversity.

The Nama assemblage is bounded from the earlier White Sea assemblage and later Cambrian period by two major episodes of faunal turnover, considered to be pulses of the end-Ediacaran extinction. [3] The genus diversity was lower than in the earlier Ediacaran and later Fortunian biotas, a fact that has been shown to be independent of sampling bias. Nonetheless, the decline in Ediacaran biota taxa was accompanied by a rise in sessile eumetazoans, with new developments such as the rise of predation and biomineralization. [10] [11] Another decline in diversity has been also proposed around c. 545 Ma. [3]

Early decline

The decline in biodiversity from the previous White Sea assemblage has been argued to have been caused by decreasing sea oxygen levels, favoring the survival of animals with a higher surface-to-volume ratio. [5] This was, however, contested by findings showing a decline in both hard-bodied and soft-bodied fauna starting before the fall in oxygen levels. Under this model, the widespread anoxia in deeper waters would have minimally affected the Ediacaran fauna, largely concentrated in shallow water areas in continental shelf settings like the Nama Group. [12] [3] Conversely, ecological change may have been responsible for the decline in oxygen levels. [13]

Biota

The soft-bodied Ediacaran biota of the Nama assemblage, in decline compared to the White Sea assemblage, was dominated by erniettomorphs, although rangeomorphs, arboreomorphs and dipleurozoans were also present. [3]

While the Late Ediacaran assemblages are mostly temporally stratified, holdovers from the Avalon and White Sea assemblages were present later than 550 million years ago, and are usually assigned to the Nama assemblage on a chronological basis regardless of biological affinity. These include Hiemalora , Charnia and the arboreomorph Arborea . However, some definitions exclude these organisms from the Nama assemblage, distinguishing it from the temporal Terminal Ediacaran biozone. [3]

The benthic, calcified Namacalathus is only known from the Nama assemblage, although its affiliations remain disputed. [3]

Tubular organisms

The first traces of the tubular cloudinids appear in the Nama assemblage, including both the mineralized Cloudina and the softer-bodied Conotubus. Other tubular organisms are known, such as Namacalathus , Sinotubulites , Corumbella and Gaojiashania . [3]

Related Research Articles

<span class="mw-page-title-main">Ediacaran</span> Third and last period of the Neoproterozoic Era

The Ediacaran is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.

The cloudinids, an early metazoan family containing the genera Acuticocloudina, Cloudina and Conotubus, lived in the late Ediacaran period about 550 million years ago. and became extinct at the base of the Cambrian. They formed millimetre-scale conical fossils consisting of calcareous cones nested within one another; the appearance of the organism itself remains unknown. The name Cloudina honors the 20th-century geologist and paleontologist Preston Cloud.

<span class="mw-page-title-main">Vendobionta</span> Group of extinct creatures that were part of the Ediacaran biota

Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, it would be the oldest of the animals that populated the Earth about 580 million years ago, in the Ediacaran period. They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna forming groups more recognizably related to modern animals. It is very likely that the whole Ediacaran biota is not a monophyletic clade and not every genus placed in its subtaxa is an animal.

Namacalathus is a problematic metazoan fossil occurring in the latest Ediacaran. The first, and only described species, N. hermanastes, was first described in 2000 from the Nama Group of central and southern Namibia.

Namapoikia rietoogensis is among the earliest known animals to produce a calcareous skeleton. Known from the Ediacaran period, before the Cambrian explosion of calcifying animals, the long-lived organism grew up to a metre in diameter and resembles a colonial sponge. It was an encruster, filling vertical fissures in the reefs in which it originally grew.

<span class="mw-page-title-main">Ediacaran biota</span> Life of the Ediacaran period

The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

The end-Ediacaran extinction is a mass extinction believed to have occurred near the end of the Ediacaran period, the final period of the Proterozoic eon. Evidence suggesting that such a mass extinction occurred includes a massive reduction in diversity of acritarchs, the sudden disappearance of the Ediacara biota and calcifying organisms, and the time gap before Cambrian organisms "replaced" them. Some lines of evidence suggests that there may have been two distinct pulses of the extinction event, one occurring 550 million years ago and the other 539 million years ago.

The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.

The Cambrian explosion is an interval of time approximately 538.8 million years ago in the Cambrian period of the early Paleozoic when a sudden radiation of complex life occurred, and practically all major animal phyla started appearing in the fossil record. It lasted for about 13 to 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well.

<i>Eoandromeda</i> Species of Ediacaran animal

Eoandromeda is an Ediacaran organism consisting of eight radial spiral arms, and known from two taphonomic modes: the standard Ediacara type preservation in Australia, and as carbonaceous compressions from the Doushantuo formation of China, where it is abundant.

<span class="mw-page-title-main">Stratigraphy of the Cambrian</span>

The Stratigraphy of the Cambrian period currently has several schemes used for ordering geologic formations from the period. The International Commission on Stratigraphy−ICS scheme has set a stratotype section for the base of the Cambrian, dated quite accurately to 538.8 ± 0.2 million years ago. Russian and Chinese scientists have developed a different scheme.

<span class="mw-page-title-main">Avalon explosion</span> Proposed evolutionary event in the history of metazoa, producing the Ediacaran biota

The Avalon explosion, named from the Precambrian faunal trace fossils discovered on the Avalon Peninsula in Newfoundland, eastern Canada, is a proposed evolutionary radiation of prehistoric animals about 575 million years ago in the Ediacaran period, with the Avalon explosion being one of three eras grouped in this time period. This evolutionary event is believed to have occurred some 33 million years earlier than the Cambrian explosion, which had been long thought to be when complex life started on Earth.

<span class="mw-page-title-main">Nama Group</span>

The Nama Group is a 125,000 square kilometres (48,000 sq mi) megaregional Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. The Nama Basin is a peripheral foreland basin, and the Nama Group was deposited in two early basins, the Zaris and Witputs, to the north, while the South African Vanrhynsdorp Group was deposited in the southern third. The Nama Group is made of fluvial and shallow-water marine sediments, both siliciclastic and carbonate. La Tinta Group in Argentina is considered equivalent to Nama Group.

<span class="mw-page-title-main">Mistaken Point Formation</span>

The Mistaken Point Formation is a geologic formation in Newfoundland and Labrador. It is recognized as a Lagerstätte preserving fossils dating back to the Ediacaran period. It contains a stratum dated to 565 ± 3 million years ago.

<span class="mw-page-title-main">Petalonamae</span> Proposed extinct group of animals

The petalonamids (Petalonamae) are an extinct group of archaic animals typical of the Ediacaran biota, also called frondomorphs, dating from approximately 635 million years ago to 516 million years ago. They are benthic and motionless animals, that have the shape of leaves, fronds (frondomorphic), feathers or spindles and were initially considered algae, octocorals or sea pens. It is now believed that there are no living descendants of the group, which shares a probable relation to the Ediacaran animals known as Vendozoans.

Atakia is a genus of animals that were members of the Ediacaran fauna, which existed from 635 to 541 million years ago. Discovered in Ukraine in 1979 by Palij, the genus Atakia are soft-bodied Metazoan cast in Vendian sediments found on the Eastern European Platform formations. Oftentimes the genus Atakia is used as a comparison to other genera, because very little information is known about this genus. There is a discontinuity in identification because the genus Fustiglyphus Vialov is debated to be the same as Atakia but found in different regions.

Shuhai Xiao is a Chinese-American paleontologist and professor of geobiology at Virginia Tech, Blacksburg, Virginia, U.S.A.

<span class="mw-page-title-main">White Sea assemblage</span> Ediacaran biotic assemblage

The White Sea assemblage was the second of the three Late Ediacaran biotic assemblages, following the Avalon assemblage and preceding the Nama assemblage. It spanned from c. 560 Ma to c. 550 Ma. Showing an increase in genus diversity from the Avalon assemblage, it concluded with a faunal turnover often characterized as the first pulse of the end-Ediacaran extinction, with only 20% of White Sea taxa found in the later Nama assemblage despite similar taphonomic processes.

<span class="mw-page-title-main">Avalon assemblage</span> Ediacaran biotic assemblage

The Avalon assemblage was the first of the three Late Ediacaran biotic assemblages, spanning from c. 575 Ma to c. 560 Ma. It was followed by the White Sea assemblage, although temporal overlaps have been noted between the biotic assemblages. While earlier macroscopic fossils, mostly of algal origin, are known from the Lantian Formation, Avalon-type localities provide the first evidence of putative metazoan ancestors, as part of the Ediacaran biota.

References

  1. ↑ Shen, Bing; Dong, Lin; Xiao, Shuhai; Kowalewski, Michal (4 January 2008). "The Avalon explosion: evolution of Ediacara morphospace". Science. 319 (5859): 81–84. Bibcode:2008Sci...319...81S. doi:10.1126/science.1150279. ISSN   1095-9203. PMID   18174439.
  2. ↑ Shi, Wei; Li, Chao; Luo, Genming; Huang, Junhua; Algeo, Thomas J.; Jin, Chengsheng; Zhang, Zihu; Cheng, Meng (24 January 2018). "Sulfur isotope evidence for transient marine-shelf oxidation during the Ediacaran Shuram Excursion". Geology. 46 (3): 267–270. doi:10.1130/G39663.1.
  3. 1 2 3 4 5 6 7 8 9 10 11 Wood, Rachel; Bowyer, Fred T.; Alexander, Ruaridh; Yilales, Mariana; Uahengo, Collen-Issia; Kaputuaza, Kavevaza; Ndeunyema, Junias; Curtis, Andrew (September 2023). "New Ediacaran biota from the oldest Nama Group, Namibia (Tsaus Mountains), and re-definition of the Nama Assemblage". Geological Magazine. 160 (9): 1673–1686. Bibcode:2023GeoM..160.1673W. doi:10.1017/S0016756823000638. hdl: 20.500.11820/bc8c23b0-d59c-4230-a45b-db854a8ad0f3 . ISSN   0016-7568.
  4. ↑ Bowyer, Fred T.; Uahengo, Collen-Issia; Kaputuaza, Kavevaza; Ndeunyema, Junias; Yilales, Mariana; Alexander, Ruaridh D.; Curtis, Andrew; Wood, Rachel A. (15 October 2023). "Constraining the onset and environmental setting of metazoan biomineralization: The Ediacaran Nama Group of the Tsaus Mountains, Namibia". Earth and Planetary Science Letters. 620: 118336. Bibcode:2023E&PSL.62018336B. doi:10.1016/j.epsl.2023.118336. ISSN   0012-821X.
  5. 1 2 3 Evans, Scott D.; Tu, Chenyi; Rizzo, Adriana; Surprenant, Rachel L.; Boan, Phillip C.; McCandless, Heather; Marshall, Nathan; Xiao, Shuhai; Droser, Mary L. (15 November 2022). "Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition". Proceedings of the National Academy of Sciences. 119 (46): e2207475119. Bibcode:2022PNAS..11907475E. doi: 10.1073/pnas.2207475119 . ISSN   0027-8424. PMC   9674242 . PMID   36343248.
  6. ↑ Bottjer, David J.; Clapham, Matthew E. (2006). Xiao, Shuhai; Kaufman, Alan J. (eds.). Evolutionary Paleoecology of Ediacaran Benthic Marine Animals. Dordrecht: Springer Netherlands. pp. 91–114. doi:10.1007/1-4020-5202-2_4. ISBN   978-1-4020-5202-6.
  7. ↑ Hofmann, Hans J.; Mountjoy, Eric W. (2001). "Namacalathus-Cloudina assemblage in Neoproterozoic Miette Group (Byng Formation), British Columbia: Canada's oldest shelly fossils". Geology. 29 (12): 1091. Bibcode:2001Geo....29.1091H. doi:10.1130/0091-7613(2001)029<1091:NCAINM>2.0.CO;2. ISSN   0091-7613.
  8. 1 2 Waggoner, Ben (1 February 2003). "The Ediacaran Biotas in Space and Time". Integrative and Comparative Biology. 43 (1): 104–113. doi:10.1093/icb/43.1.104. ISSN   1540-7063. PMID   21680415.
  9. ↑ Boag, Thomas H.; Darroch, Simon A. F.; Laflamme, Marc (November 2016). "Ediacaran distributions in space and time: testing assemblage concepts of earliest macroscopic body fossils". Paleobiology. 42 (4): 574–594. Bibcode:2016Pbio...42..574B. doi:10.1017/pab.2016.20. ISSN   0094-8373.
  10. 1 2 Muscente, A. D.; Bykova, Natalia; Boag, Thomas H.; Buatois, Luis A.; Mángano, M. Gabriela; Eleish, Ahmed; Prabhu, Anirudh; Pan, Feifei; Meyer, Michael B.; Schiffbauer, James D.; Fox, Peter; Hazen, Robert M.; Knoll, Andrew H. (2019-02-22). "Ediacaran biozones identified with network analysis provide evidence for pulsed extinctions of early complex life". Nature Communications. 10 (1): 911. Bibcode:2019NatCo..10..911M. doi:10.1038/s41467-019-08837-3. ISSN   2041-1723. PMC   6384941 . PMID   30796215.
  11. ↑ Schiffbauer, James D; Huntley, John Warren; O'Neil, Gretchen R.; Darroch, Simon A.F.; Laflamme, Marc; Cai, Yaoping (November 2011). "The Latest Ediacaran Wormworld Fauna: Setting the Ecological Stage for the Cambrian Explosion". Geological Society of America. 26 (11): 4–11.
  12. ↑ Tostevin, Rosalie; Clarkson, Matthew O.; Gangl, Sophie; Shields, Graham A.; Wood, Rachel A.; Bowyer, Fred; Penny, Amelia M.; Stirling, Claudine H. (2019-01-15). "Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans". Earth and Planetary Science Letters. 506: 104–112. Bibcode:2019E&PSL.506..104T. doi:10.1016/j.epsl.2018.10.045. hdl: 20.500.11820/25fe1837-1045-4698-bdb8-4516c7b26a38 . ISSN   0012-821X.
  13. ↑ Lenton, Timothy M.; Daines, Stuart J. (2018). "The effects of marine eukaryote evolution on phosphorus, carbon and oxygen cycling across the Proterozoic–Phanerozoic transition". Emerging Topics in Life Science. 2 (2): 267–278. doi:10.1042/ETLS20170156. PMC   7289021 . PMID   32412617.
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