The molecular record of Cryogenian sponges – a response to Antcliffe (2013)

Love, Gordon D.; Summons, Roger E.

doi:10.1111/pala.12196

Cited by 39 publications

(52 citation statements)

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“…For example, the presence of abundant mid‐chain monomethylalkanes found in the silicilyte, the overall elevated %C 29 sterane contents, and the presence of elevated 24 ipc/npc ratios are distinctive traits Neoproterozoic to early Cambrian rocks. Such biomarkers and biomarker ratio values are not observed in routine laboratory contaminants or typical drilling fluids (Love & Summons, ).…”

Section: Resultsmentioning

confidence: 99%

“…However, as discussed, distinctive, coherent trends and strong differences in biomarker ratios are seen not only between the silicilyte and bounding shales, but also within the specific formations themselves (e.g., Figures and ). Furthermore, our measured biomarker ratio values are consistent with those measured previously on samples from these formations (Table ; Grosjean et al., ; Love et al., ; Love et al., ). Biomarker ratios in the units are distinctive for the time period (the late Neoproterozoic), including the presence of the discussed series of mid‐chain methyl alkanes, high %C 29 sterane ratios, and high 24‐ipc/npc ratios (Grantham, ; Grosjean et al., ; Kelly et al., ; Love & Summons, ; Love et al., ; McCaffrey et al., ; Peters et al., , ). Phanerozoic oils would be unlikely to introduce biomarkers with these characteristics. Biomarker ratios derived from the kerogen‐bound biomarker pool through hydropyrolysis of kerogen from other Athel shale and silicilyte samples—as discussed above, a method that is less susceptible to contamination by migrated hydrocarbons—show similar differences between the shales and silicilyte as do the measurements of bitumens (Table ).…”

Section: Resultsmentioning

confidence: 99%

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Paleoecology and paleoceanography of the Athel silicilyte, Ediacaran–Cambrian boundary, Sultanate of Oman

et al. 2017

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The Athel silicilyte is an enigmatic, hundreds of meters thick, finely laminated quartz deposit, in which silica precipitated in deep water (>~100-200 m) at the Ediacaran-Cambrian boundary in the South Oman Salt Basin. In contrast, Meso-Neoproterozoic sinks for marine silica were dominantly restricted to peritidal settings. The silicilyte is known to contain sterane biomarkers for demosponges, which today are benthic, obligately aerobic organisms. However, the basin has previously been described as permanently sulfidic and time-equivalent shallow-water carbonate platform and evaporitic facies lack silica. The Athel silicilyte thus represents a unique and poorly understood depositional system with implications for late Ediacaran marine chemistry and paleoecology. To address these issues, we made petrographic observations, analyzed biomarkers in the solvent-extractable bitumen, and measured whole-rock iron speciation and oxygen and silicon isotopes. These data indicate that the silicilyte is a distinct rock type both in its sedimentology and geochemistry and in the original biology present as compared to other facies from the same time period in Oman. The depositional environment of the silicilyte, as compared to the bounding shales, appears to have been more reducing at depth in sediments and possibly bottom waters with a significantly different biological community contributing to the preserved biomarkers. We propose a conceptual model for this system in which deeper, nutrient-rich waters mixed with surface seawater via episodic mixing, which stimulated primary production. The silica nucleated on this organic matter and then sank to the seafloor, forming the silicilyte in a sediment-starved system. We propose that the silicilyte may represent a type of environment that existed elsewhere during the Neoproterozoic. These environments may have represented an important locus for silica removal from the oceans.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Paleoecology and paleoceanography of the Athel silicilyte, Ediacaran–Cambrian boundary, Sultanate of Oman

et al. 2017

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“…We can say that no other lineage of eukaryotes besides sponges is known to have the genetic toolkit necessary to generate such sterols and to have lived in the Neoproterozoic. Combined with recent rebuttals against putative sample contamination and alternate hypotheses of sterol diagenesis (42), there appears to be no current viable alternative to a sponge origin for Neoproterozoic 24-isopropylcholestanes. Perhaps the last major challenge against the sponge biomarker hypothesis is the "ghost lineage" linking this sterane to the oldest unambiguous fossils of siliceous sponges, which has previously been estimated at >100 million y (8).…”

Section: Stramenopiles IImentioning

confidence: 99%

Sterol and genomic analyses validate the sponge biomarker hypothesis

Gold

Grabenstatter

Mendoza

et al. 2016

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

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117

121

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Molecular fossils (or biomarkers) are key to unraveling the deep history of eukaryotes, especially in the absence of traditional fossils. In this regard, the sterane 24-isopropylcholestane has been proposed as a molecular fossil for sponges, and could represent the oldest evidence for animal life. The sterane is found in rocks ∼650-540 million y old, and its sterol precursor (24-isopropylcholesterol, or 24-ipc) is synthesized today by certain sea sponges. However, 24-ipc is also produced in trace amounts by distantly related pelagophyte algae, whereas only a few close relatives of sponges have been assayed for sterols. In this study, we analyzed the sterol and gene repertoires of four taxa (Salpingoeca rosetta, Capsaspora owczarzaki, Sphaeroforma arctica, and Creolimax fragrantissima), which collectively represent the major living animal outgroups. We discovered that all four taxa lack C 30 sterols, including 24-ipc. By building phylogenetic trees for key enzymes in 24-ipc biosynthesis, we identified a candidate gene (carbon-24/28 sterol methyltransferase, or SMT) responsible for 24-ipc production. Our results suggest that pelagophytes and sponges independently evolved C 30 sterol biosynthesis through clade-specific SMT duplications. Using a molecular clock approach, we demonstrate that the relevant sponge SMT duplication event overlapped with the appearance of 24-isopropylcholestanes in the Neoproterozoic, but that the algal SMT duplication event occurred later in the Phanerozoic. Subsequently, pelagophyte algae and their relatives are an unlikely alternative to sponges as a source of Neoproterozoic 24-isopropylcholestanes, consistent with growing evidence that sponges evolved long before the Cambrian explosion ∼542 million y ago.sponges | Porifera | sterols | steranes | Amorphea

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“…Several additional rock formations aged between 2.4 and 1.4 Ga have been suggested to contain indigenous molecular eukaryotic fossils (Pawlowska et al, 2013), but none of these have been fully accepted by the wider scientific community. Thus, the oldest unambiguous molecular fossils of eukaryotes are from the 0.7-to 0.63-Ga Huqf Supergroup of Oman in the form of 24-isopropylcholestanes derived from Demosponges (Love and Summons, 2015;Love et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

The changing view of eukaryogenesis – fossils, cells, lineages and how they all come together

Dacks

Field

Buick

et al. 2016

Journal of Cell Science

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Eukaryogenesis -the emergence of eukaryotic cells -represents a pivotal evolutionary event. With a fundamentally more complex cellular plan compared to prokaryotes, eukaryotes are major contributors to most aspects of life on Earth. For decades, we have understood that eukaryotic origins lie within both the Archaea domain and α-Proteobacteria. However, it is much less clear when, and from which precise ancestors, eukaryotes originated, or the order of emergence of distinctive eukaryotic cellular features. Many competing models for eukaryogenesis have been proposed, but until recently, the absence of discriminatory data meant that a consensus was elusive. Recent advances in paleogeology, phylogenetics, cell biology and microbial diversity, particularly the discovery of the 'Candidatus Lokiarcheaota' phylum, are now providing new insights into these aspects of eukaryogenesis. The new data have allowed the time frame during which eukaryogenesis occurred to be finessed, a more precise identification of the contributing lineages and the biological features of the contributors to be clarified. Considerable advances have now been used to pinpoint the prokaryotic origins of key eukaryotic cellular processes, such as intracellular compartmentalisation, with major implications for models of eukaryogenesis.

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The molecular record of Cryogenian sponges – a response to Antcliffe (2013)

Cited by 39 publications

References 54 publications

Paleoecology and paleoceanography of the Athel silicilyte, Ediacaran–Cambrian boundary, Sultanate of Oman

Paleoecology and paleoceanography of the Athel silicilyte, Ediacaran–Cambrian boundary, Sultanate of Oman

Sterol and genomic analyses validate the sponge biomarker hypothesis

The changing view of eukaryogenesis – fossils, cells, lineages and how they all come together

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