{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,5]],"date-time":"2026-04-05T00:12:02Z","timestamp":1775347922094,"version":"3.50.1"},"reference-count":114,"publisher":"Portland Press Ltd.","issue":"2","content-domain":{"domain":["portlandpress.com"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2018,9,28]]},"abstract":"<jats:p>Through much of the Proterozoic Eon (2.5\u20130.54 billion years ago, Ga), oceans were dominantly anoxic. It is often assumed that this put a brake on early eukaryote diversification because eukaryotes lived only in oxygenated habitats, which were restricted to surface waters and benthic environments near cyanobacterial mats. Studies of extant microbial eukaryotes show, however, that they are diverse and abundant in anoxic (including sulfidic) environments, often through partnerships with endo- and ectosymbiotic bacteria and archaea. Though the last common ancestor of extant eukaryotes was capable of aerobic respiration, we propose that at least some, and perhaps many, early eukaryotes were adapted to anoxic settings, and outline a way to test this with the microfossil and redox-proxy record in Proterozoic shales. This hypothesis might explain the mismatch between the record of eukaryotic body fossils, which extends back to &amp;gt;1.6\u2005Ga, and the record of sterane biomarkers, which become diverse and abundant only after 659\u2005Ma, as modern eukaryotes adapted to anoxic habitats do not make sterols (sterane precursors). In addition, an anoxic habitat might make sense for several long-ranging (&amp;gt;800 million years) and globally widespread eukaryotic taxa, which disappear in the late Neoproterozoic around the time oxic environments are thought to have become more widespread.<\/jats:p>","DOI":"10.1042\/etls20170162","type":"journal-article","created":{"date-parts":[[2018,7,13]],"date-time":"2018-07-13T09:46:53Z","timestamp":1531475213000},"page":"299-309","update-policy":"https:\/\/doi.org\/10.1042\/crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Anoxic ecosystems and early eukaryotes"],"prefix":"10.1042","volume":"2","author":[{"given":"Susannah M.","family":"Porter","sequence":"additional","affiliation":[{"name":"Department of Earth Science, University of California at Santa Barbara, Santa Barbara, CA 93106, U.S.A."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Heda","family":"Agi\u0107","sequence":"additional","affiliation":[{"name":"Department of Earth Science, University of California at Santa Barbara, Santa Barbara, CA 93106, U.S.A."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Leigh Anne","family":"Riedman","sequence":"additional","affiliation":[{"name":"Department of Earth Science, University of California at Santa Barbara, Santa Barbara, CA 93106, U.S.A."}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"288","published-online":{"date-parts":[[2018,7,13]]},"reference":[{"key":"2021111608102716300_ETLS-2017-0162CC1","doi-asserted-by":"publisher","first-page":"1137","DOI":"10.1126\/science.1069651","article-title":"Proterozoic ocean chemistry and evolution: a bioinorganic bridge?","volume":"297","author":"Anbar","year":"2002","journal-title":"Science"},{"key":"2021111608102716300_ETLS-2017-0162CC2","doi-asserted-by":"crossref","first-page":"414","DOI":"10.1017\/CBO9780511933875.028","volume-title":"Origins and evolution of life: an astrobiology perspective","author":"Javaux","year":"2011"},{"key":"2021111608102716300_ETLS-2017-0162CC3","doi-asserted-by":"publisher","first-page":"a016121","DOI":"10.1101\/cshperspect.a016121","article-title":"Paleobiological perspectives on early eukaryotic evolution","volume":"6","author":"Knoll","year":"2014","journal-title":"Cold Spring Harbor Perspect. 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