Research ArticlePALEOECOLOGY

Cryogenian evolution of stigmasteroid biosynthesis

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Science Advances  20 Sep 2017:
Vol. 3, no. 9, e1700887
DOI: 10.1126/sciadv.1700887
  • Fig. 1 Evolutionary radiation of stigmasteroid (24) biosynthesis.

    (A) Tonian rocks are nearly exclusively characterized by C27 steranes [cholestane; see (F): Green symbols denote C27 dominance and complete absence of C29 steranes, with only sporadic traces of C28 4-desmethylsteranes]. (B) The oldest noncontaminated C29 24-ethylsteranes [stigmastane; see (F): yellow symbols stand for C27 > C29, whereas red symbols indicate C27 < C29 and often C27 ≪ C29] only appear during the latest Cryogenian (Marinoan deglaciation) and earliest Ediacaran in Oman, whereas contemporaneous rocks from three other localities are still strongly or exclusively dominated by C27 steranes, indicating a 720- to 635-Ma Snowball Earth glacial origin of the stigmasteroid biosynthetic pathway—in agreement with the physiological membrane density advantage yielded by cellular phytosterols (19, 20) and molecular clocks (30). (C and D) Global dominance of C29 steroid biosynthesis by 600 Ma (table S1) highlights the evolutionary advantage of the likely chlorophyte host organism and a rapid rise to ecological dominance. (E) Schematic representation of Neoproterozoic time showing steroidal dominance (green, C27 versus red, C29) and the time brackets from (A) to (D). (F) Relevant molecular structures and schematic tandem-MS chromatograms of (bottom to top) C27 [green, mass/charge ratio (m/z) 372 to 217], C28 (yellow, m/z 386 to 217), and C29 (red, m/z 400 to 217) steranes, emphasizing the color code used in (A) to (D). Ages on the top right of the maps comply with the palaeogeographic snapshots after (31).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/9/e1700887/DC1

    Supplementary Text

    fig. S1. Molecular clock analysis of SMT genes (30) reveals a divergence of green algae during the Late Cryogenian.

    fig. S2. Studied sample locations on a modern continental configuration.

    fig. S3. Studied sample locations in a palaeogeographic context after (31).

    fig. S4. Estimated maximum time brackets of the studied samples.

    fig. S5. Hydropyrolysis of an earliest Ediacaran cap carbonate sample from the Mirassol d’Oeste Fm verifies the C27 sterane–dominated signature found in other samples from this unit and confirms their syngenicity to the host rock.

    table S1. Steranes in Neoproterozoic rocks.

    table S2. Unsuitable samples.

    References (34122)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. Molecular clock analysis of SMT genes (30) reveals a divergence of green algae during the Late Cryogenian.
    • fig. S2. Studied sample locations on a modern continental configuration.
    • fig. S3. Studied sample locations in a palaeogeographic context after (31).
    • fig. S4. Estimated maximum time brackets of the studied samples.
    • fig. S5. Hydropyrolysis of an earliest Ediacaran cap carbonate sample from the Mirassol d’Oeste Fm verifies the C27 sterane–dominated signature found in other samples from this unit and confirms their syngenicity to the host rock.
    • Legend for table S1
    • table S2. Unsuitable samples.
    • References (34–122)

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    Other Supplementary Material for this manuscript includes the following:

    • table S1 (.pdf format). Steranes in Neoproterozoic rocks.

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