The DOI matches its Crossref record; 54 of the 54 references it cites were found in a registry or an index; 3 of the 31 sources its claims cite were checked for support.
Oxygen requirements of the earliest animals
Open accessAbstract
A rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. In this scenario, Earth's surface environment failed to meet the high oxygen requirements of animals up until the middle to late Neoproterozoic Era (850-542 million years ago), when oxygen concentrations sufficiently rose to permit the existence of animal life for the first time. Although multiple lines of geochemical evidence support an oxygenation of the Ediacaran oceans (635-542 million years ago), roughly corresponding with the first appearance of metazoans in the fossil record, the oxygen requirements of basal animals remain unclear. Here we show that modern demosponges, serving as analogs for early animals, can survive under low-oxygen conditions of 0.5-4.0% present atmospheric levels. Because the last common ancestor of metazoans likely exhibited a physiology and morphology similar to that of a modern sponge, its oxygen demands may have been met well before the enhanced oxygenation of the Ediacaran Period. Therefore, the origin of animals may not have been triggered by a contemporaneous rise in the oxygen content of the atmosphere and oceans. Instead, other ecological and developmental processes are needed to adequately explain the origin and earliest evolution of animal life on Earth.
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Claims the paper makes
18 Own interpretation · 10 No full text of the sources · 5 Own result · 5 No basis given · 2 Partly supported · 2 Sources not found · 1 Supported so far · 1 Not checked yet · accuracy not yet measured
The cited sources support only part of this claim — read each source’s verdict below.
In the paper
“Internal anoxia, however, does appear to be a common feature of sponge physiology (34,35).”
§ Oxygen requirements of the earliest animals > Results and Discussion
What the sources say
- Not checked — no full text of the sourcecites [34] 34. Hoffmann F, et al. (2005) An anaerobic world in sponges. Geomicrobiol J 22(1-2):1-10. source
- Partly supportedcites [35] 35. Hoffmann F, et al. (2008) Oxygen dynamics and transport in the Mediterranean sponge Aplysina aerophoba. Mar Biol 153(6):1257-1264. sourceExperimental — accuracy not yet measured
The Abstract and the Discussion section on oxygen dynamics report internal anoxia in non-pumping A. aerophoba, with tissue becoming anoxic within 15 minutes after pumping stops. They do not establish that internal anoxia is common across sponges; the Discussion also notes that prolonged non-pumping was not observed in an in situ study of A. aerophoba unless the sponge was disturbed. (LLM, conf=0.88)
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In the paper
“Overall, the patterns of oxygen uptake observed during the initial drawdown to anoxia followed Michaelis-Menten kinetics, with a V max of 2.42% air saturation/h•g dry weight , or 7.93 μM O 2 /h•g dry weight , and a K m of 4.86% of air saturation, or 15.9 μM O 2 , at the water salinity and temperature of our experiments (Fig. 3).”
§ Oxygen requirements of the earliest animals > Results and Discussion
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In the paper
“Here we show that modern demosponges, serving as analogs for early animals, can survive under low-oxygen conditions of 0.5-4.0%present atmospheric levels.”
plainSingle case- Asserted: passes — The authors put it forward as true.
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In the paper
“Sponges were also observed on the Volcano 7 seamount in the eastern tropical Pacific, where oxygen concentrations ranged from 4.5 to 7.2 μM O 2 (31) .”
§ Oxygen requirements of the earliest animals > Significance
What the sources say
- Not checked — no full text of the sourcecites [31] 31. Levin LA, Huggett CL, Wishner KF (1991) Control of deep-sea benthic community structure by oxygen and organic matter gradients in the eastern Pacific Ocean. J Mar Res 49(4):763-800. source
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“Therefore, the origin of animals may not have been triggered by a contemporaneous rise in the oxygen content of the atmosphere and oceans.”
hedged- Asserted: passes — The authors put it forward as true.
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In the paper
“Because the last common ancestor of metazoans likely exhibited a physiology and morphology similar to that of a modern sponge, its oxygen demands may have been met well before the enhanced oxygenation of the Ediacaran Period.”
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In the paper
“It would appear, then, that LMA sponges, such as H. panicea, may be better adapted to lowoxygen conditions than HMA sponges.”
§ Oxygen requirements of the earliest animals > Results and Discussion
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In the paper
“Numerous phylogenetic analyses conclude that sponges are the earliest diverging extant metazoan group (11,12,(20)(21)(22).”
What the sources say
- Not matchedcites (11,12,(20)(21)(22)
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“However, although these theoretical efforts provide some guidance, they are based on highly simplified, idealized organisms that do not reflect the complexity of living animals.”
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In the paper
“Choanoflagellates, in turn, are the closest living relatives of animals (24)(25)(26)(27)(28).”
What the sources say
- Not matchedcites (24)(25)(26)(27)(28)
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
plain- Asserted: passes — The authors put it forward as true.
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- It may state two separate claims as one. 15
- Probably not a substantial claim. 3
The cited sources support only part of this claim — read each source’s verdict below.
In the paper
“Indeed, oxygen levels this high may have been reached as early as the Great Oxidation Event some 2.3-2.4 billion years ago (43,45) and may have persisted at these levels through much of the intervening time (43,44), with some likely swings to lower levels, however, around 1.8 billion years ago (46).”
§ Oxygen requirements of the earliest animals > Sponge Evolution and Environmental Oxygen Levels.
What the sources say
- Not checked — no full text of the sourcecites [43] 43. Kump LR (2008) The rise of atmospheric oxygen. Nature 451(7176):277-278. source
- Not checked — no full text of the sourcecites [45] 45. Bekker A, Holland HD (2012) Oxygen overshoot and recovery during the early Pale- oproterozoic. Earth Planet Sci Lett 317-318:295-304. source
- Not checked — no full text of the sourcecites [44] 44. Canfield DE (2014) Proterozoic Atmospheric Oxygen. Treatise on Geochemistry, eds Holland HD, Turekian KK (Elsevier, Oxford), 2nd Ed., pp 197-216. source
- Partly supportedcites [46] 46. Canfield DE, et al. (2013) Oxygen dynamics in the aftermath of the Great Oxidation of Earth's atmosphere. Proc Natl Acad Sci USA 110(42):16736-16741. sourceExperimental — accuracy not yet measured
The Significance section (page unavailable) places a rise in oxygen at the Great Oxidation Event about 2.3 billion years ago, followed by elevated levels for roughly 200 million years and then a collapse. The Results and Discussion section (page unavailable) describes later low-oxygen episodes, but the paper does not establish the cited 0.5–4% PAL range or its persistence through much of the intervening time. (LLM, conf=0.85)
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The sources with a verdict support this claim; the rest weren’t checked yet, have no full text we could read, or their verdicts aren’t rated yet.
In the paper
“Indeed, according to present evidence, the earliest proposed signs of animals in the rock record (9,10), as well as molecular clock divergence estimates (11,12), predate the earliest evidence for deep ocean oxygenation (1), potentially by tens of millions of years.”
What the sources say
- Not checked — no full text of the sourcecites [9] 9. Love GD, et al. (2009) Fossil steroids record the appearance of Demospongiae during the Cryogenian period. Nature 457(7230):718-721. source
- Not checked — no full text of the sourcecites [10] 10. Maloof AC, et al. (2010) Possible animal-body fossils in pre-Marinoan limestones from South Australia. Nat Geosci 3(9):653-659. source
- Supportedcites [11] 11. Peterson KJ, Butterfield NJ (2005) Origin of the Eumetazoa: Testing ecological pre- dictions of molecular clocks against the Proterozoic fossil record. Proc Natl Acad Sci USA 102(27):9547-9552. source
The Results (page unavailable) give molecular-clock estimates for early animal divergences: the minimum-evolution analysis dates the origin of Metazoa to 664 Ma and brackets eumetazoan evolution between 634 and 604 Ma. This paper supports the molecular-clock dates attributed to citations (11,12); the separate citation (1), not this paper, is offered for the timing of deep-ocean oxygenation. (LLM, conf=0.86)
- Not checked — no full text of the sourcecites [12] 12. Erwin DH, et al. (2011) The Cambrian conundrum: Early divergence and later eco- logical success in the early history of animals. Science 334(6059):1091-1097. source
- Not checked — no full text of the sourcecites [1] 1. Sahoo SK, et al. (2012) Ocean oxygenation in the wake of the Marinoan glaciation. Nature 489(7417):546-549. source
hedgedcorrelational- Asserted: passes — The authors put it forward as true.
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In the paper
“We show that although sensitive to oxygen, H. panicea can both tolerate and grow at low oxygen levels from 0.5% to 4% PAL.”
- Also stated in: § Results and Discussion · plain
“Overall, the sponges were able to both respire and feed to oxygen levels cycling between 0.5% and 4% PAL.”
§ Oxygen requirements of the earliest animals > Significance
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- Also stated in: § Results and Discussion · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“functional gene and 16S rRNA analyses reveal a significant population of ammonium-oxidizing Archaea and betaproteobacteria, as well as other aerobic organisms (Fig. S6 and Table S1).”
§ Oxygen requirements of the earliest animals > Results and Discussion
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“Therefore, the majority of the oxygen uptake and Rhodomonas consumption observed during the experiments can be attributed to the sponges, with the background rates likely attributed to free-living microbes in our experimental system.”
§ Oxygen requirements of the earliest animals > Results and Discussion
hedgeddirect- Asserted: passes — The authors put it forward as true.
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In the paper
“Our results suggest that H. panicea is sensitive to both anoxia and prolonged exposure to relatively stagnant seawater.”
§ Oxygen requirements of the earliest animals > Results and Discussion
hedgeddirectSingle case- Asserted: passes — The authors put it forward as true.
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In the paper
“This K m is less than half of the 10% PAL serving as the estimated minimum level of atmospheric oxygen thought to have permitted the oxygenation of the deep oceans around 580 Ma (2), as well as the level estimated to permit the existence of millimeter-width, diffusionlimited animals (15).”
§ Oxygen requirements of the earliest animals > Results and Discussion
What the sources say
- Not checked — no full text of the sourcecites [2] 2. Canfield DE, Poulton SW, Narbonne GM (2007) Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life. Science 315(5808):92-95. source
- Not checked — no full text of the sourcecites [15] 15. Catling DC, Glein CR, Zahnle KJ, McKay CP (2005) Why O2 is required by complex life on habitable planets and the concept of planetary "oxygenation time" Astrobiology 5(3):415-438. source
hedgedSingle case- Asserted: passes — The authors put it forward as true.
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In the paper
“Although levels of atmospheric oxygen may have reached 10% PAL by 580 Ma, the geochemical record does not preclude oxygen levels of 0.5-4% PAL during the Cryogenian Period (43,44).”
§ Oxygen requirements of the earliest animals > Sponge Evolution and Environmental Oxygen Levels.
What the sources say
- Not checked — no full text of the sourcecites [43] 43. Kump LR (2008) The rise of atmospheric oxygen. Nature 451(7176):277-278. source
- Not checked — no full text of the sourcecites [44] 44. Canfield DE (2014) Proterozoic Atmospheric Oxygen. Treatise on Geochemistry, eds Holland HD, Turekian KK (Elsevier, Oxford), 2nd Ed., pp 197-216. source
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In the paper
“Such evidence can reasonably be obtained by studying modern animals that resemble the earliest metazoans.”
plainconditional- Asserted: passes — The authors put it forward as true.
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Probably not a substantial claim. The paper may give no reason why it holds.
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In the paper
“Given the complete absence of necrosis in the sponges maintained at both low and high oxygen levels during this run, the necrosis observed during experiment 1 was likely due to the infrequent exchange of fresh seawater and not necessarily the low oxygen levels.”
§ Oxygen requirements of the earliest animals > Results and Discussion
hedgedconditional- Asserted: passes — The authors put it forward as true.
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In the paper
“This suggests that although 3-4% PAL oxygen may not compromise H. panicea's growth or maintenance of healthy tissue, anoxia still does.”
§ Oxygen requirements of the earliest animals > Results and Discussion
hedgeddirectSingle case- Asserted: passes — The authors put it forward as true.
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In the paper
“This suggests that the similarities between choanocytes and choanoflagellates were inherited from a common ancestor and that the choanocytebased feeding mode, as retained by sponges, is likely ancestral to all animals (29).”
What the sources say
- Not checked — no full text of the sourcecites [29] 29. Nichols SA, Dayel MJ, King N (2009) Genomic, phylogenetic, and cell biological in- sights into metazoan origins. Animal Evolution: Genes, Genomes, Fossils and Trees, eds Telford MJ, Littlewood DTJ (Oxford University Press, Oxford), pp 24-32. source
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In the paper
“Furthermore, to establish that low levels of atmospheric oxygen, in fact, delayed the origin of animal life on Earth, it is necessary to know the minimum oxygen requirements of early animals.”
plaindirect- Asserted: passes — The authors put it forward as true.
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Probably not a substantial claim.
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In the paper
“Therefore, to more conclusively determine the minimum oxygen requirements of metazoans, direct experimental evidence is required.”
boosted- Asserted: passes — The authors put it forward as true.
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Probably not a substantial claim. It may be too vague to check against evidence.
None of the sources cited for this claim have been checked yet.
In the paper
“LMA sponges are known to have shorter and wider water canals (38), as well as larger choanoflagellate chambers (39), than high-microbial abundance (HMA) sponges.”
§ Oxygen requirements of the earliest animals > Results and Discussion
What the sources say
- Not checked — no full text of the sourcecites [38] 38. Vacelet J, Donadey C (1977) Electron-microscope study of association between some sponges and bacteria. J Exp Mar Biol Ecol 30(3):301-314. source
- Not matchedcites [39] 39. Boury-Esnault N, de Vos L, Donadey C, Vacelet J (1990) Ultrastructure of Choanosome and Sponge Classification (Smithsonian Institution Press, Washington, DC), pp 237-244.
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
boostedcorrelational- Asserted: passes — The authors put it forward as true.
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A conclusion the paper draws from its own results — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Under this scenario, the origin of animal life was not a response to atmospheric oxygenation but part of the ecological reworking of marine biogeochemical cycles.”
§ Oxygen requirements of the earliest animals > Sponge Evolution and Environmental Oxygen Levels.
plain- Asserted: passes — The authors put it forward as true.
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In the paper
“Recent molecular clock estimates place the last common ancestor of all sponges at nearly 800 Ma (12), whereas putative sponge-like body fossils are found in rocks dated between 660 and 635 Ma (10) in the Cryogenian Period (850-635 Ma).”
§ Oxygen requirements of the earliest animals > Sponge Evolution and Environmental Oxygen Levels.
What the sources say
- Not checked — no full text of the sourcecites [12] 12. Erwin DH, et al. (2011) The Cambrian conundrum: Early divergence and later eco- logical success in the early history of animals. Science 334(6059):1091-1097. source
- Not checked — no full text of the sourcecites [10] 10. Maloof AC, et al. (2010) Possible animal-body fossils in pre-Marinoan limestones from South Australia. Nat Geosci 3(9):653-659. source
hedged- Asserted: passes — The authors put it forward as true.
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In the paper
“We provide experimental evidence suggesting that the last common ancestor of animals could have thrived in oxygen levels as low as 0.5% to 4% of present atmospheric levels, which were likely met on Earth well before animals evolved.”
§ Oxygen requirements of the earliest animals > Significance
hedged- Asserted: passes — The authors put it forward as true.
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The paper relies on this without support.
The minimum oxygen requirements of modern sponges and their metabolic response to low oxygen had not been investigated prior to this study.
“Despite these observations, however, the minimum oxygen requirements of modern sponges and their metabolic response to low oxygen have not, to our knowledge, been investigated.”
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
The source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Indeed, under most conditions, the estimated tolerance range for basal metazoan organisms (12) is only safely exceeded throughout the year at p O2 on the order of ∼ 5 -10% PAL.”
From Earth's oxygen cycle and the evolution of animal life (2016) · cites this paper as [12]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Experimental work with the modern demosponge Halichondria panacea suggests an empirical O2 threshold of ∼ 0.5 -4.0% of the present atmospheric level (PAL; corresponding to an equilibrium concentration of ∼ 1 -10 μ mol · kg -1 for air-saturated water at 25 °C and a salinity of 35 ‰ ) for basal metazoan life (12)”
From Earth's oxygen cycle and the evolution of animal life (2016) · cites this paper as [12]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Finally, in the greater context of what triggered the emergence of complex animal ecosystems on Earth, our isotope data and models suggest that there were ample amounts of O2 for animals in the surface ocean at the onset of the Cambrian (69).”
From Atmosphere-ocean oxygen and productivity dynamics during early animal radiations (2019) · cites this paper as [69]
Experimental — accuracy not yet measuredThe cited source says what the claim attributes to it.
In the citing paper
“The early originating suspension-feeding sponges had low O2 requirements63, and may have helped consume the large dissolved organic carbon reservoir that acted as a major redox buffer in the Proterozoic ocean12.”
From Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals (2015) · cites this paper as [63]
The check wasn’t confident either way, so it gives no verdict — never disputed.
In the citing paper
“The BACE pre-dates the first appearance of Treptichnus pedum (31,32)”
From Integrated records of environmental change and evolution challenge the Cambrian Explosion (2019) · cites this paper as [31]
Experimental — accuracy not yet measured
In the citing paper
“Recent work by Mills et al. (2014), however, suggests that primitive metazoans, such as sponges, may have needed very little oxygen in the water column in order to thrive.”
From Trace elements at the intersection of marine biological and geochemical evolution (2016) · cites this paper as Mills et al., 2014
In the citing paper
“This billion-year stagnation in eukaryotic diversification is often attributed to the late rise of atmospheric oxygen (e.g., Nursall, 1959;Knoll and Carrol, 1999;Fedonkin, 2003;Planavksy et al., 2014a) to levels required by metazoans (i.e.0.5% to 4% PAL; Mills et al., 2014).”
From Trace elements at the intersection of marine biological and geochemical evolution (2016) · cites this paper as Mills et al., 2014
In the citing paper
“This level of dissolved O2 in surface waters is generally consistent with the 0.1-1% PAL proposed as necessary for early animals”
From Trace elements at the intersection of marine biological and geochemical evolution (2016) · cites this paper as Mills et al., 2014
In the citing paper
“The recognition that modern sponges can survive at very low oxygen levels (e.g.Mills et al., 2014;though it has not yet been demonstrated that they can complete their entire life cycle under such conditions) suggests that the initial evolution of animals may have taken place at lower oxygen levels than are generally assumed necessary.”
From Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota (2015) · cites this paper as Mills et al., 2014
Citations
Cites
Kasting, J. F. (1993) · Science · doi:10.1126/science.11536547 · Cited by 1,374
Erwin, D. H., Laflamme, M., Tweedt, S. M., Sperling, E. A., Pisani, D., & Peterson, K. J. (2011) · Science · doi:10.1126/science.1206375 · Cited by 1,336 · cited 3×
“Recent molecular clock estimates place the last common ancestor of all sponges at nearly 800 Ma (12), whereas putative sponge-like body fossils are found in rocks dated between 660 and 635 Ma (10) in the Cryogenian Period (850–635 Ma).”
BackgroundThe genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans
King, N., Westbrook, M. J., Young, S. L., Kuo, A., Abedin, M., Chapman, J., Fairclough, S., Hellsten, U., Isogai, Y., Letunic, I., et al. (2008) · Nature · doi:10.1038/nature06617 · Cited by 1,139
Resolving difficult phylogenetic questions: Why more sequences are not enough
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Late-Neoproterozoic Deep-Ocean Oxygenation and the Rise of Animal Life
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“3% PAL) are sufficient to support the respiration of sponges, considered good candidates for early evolved animals, whose oxygen requirements are in the range of ≤1–4% PAL (12).”
BackgroundInfluentialSelf-citation
Metadata
- Authors
- Mills, D. B., Ward, L. M., Jones, C., Sweeten, B., Forth, M., Treusch, A. H., & Canfield, D. E.
- Affiliations
- University of Southern Denmark (DK)
- California Institute of Technology (US)
- University of British Columbia (CA)
- Venue
- Proceedings of the National Academy of Sciences
- Publisher
- National Academy of Sciences
- Published
- 2014-02-18
- Volume
- 111
- Issue
- 11
- Pages
- 4168-4172
- ISSN
- 0027-8424 (ISSN-L)
- 1091-6490
- PMC
- PMC3964089
- OpenAlex
- W2029322624
- Semantic Scholar
- ac41b42cf0cc457afe8379a4d86261edcc53d9e5
- Cited by
- 355
- References
- 53
- Citations by year
- 2026: 15 · 2025: 29 · 2024: 24 · 2023: 24 · 2022: 39 · 2021: 40 · 2020: 29 · 2019: 29 · 2018: 33 · 2017: 23 · 2016: 27 · 2015: 32 · 2014: 11
- FWCI
- 22.57
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Proceedings of the National Academy of Sciences (publishedVersion)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- CaltechAUTHORS (California Institute of Technology) (submittedVersion)
- University of Southern Denmark Research Portal (University of Southern Denmark) (submittedVersion)
- Funders
- Agouron Institute
- National Research Foundation
- Danmarks Grundforskningsfond (Grant DNRF 53, DNRF 53)
- Topics
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Origins and Evolution of Life
- Keywords
- origin of animals, Ediacaran, oxygen requirement, demosponges, low oxygen tolerance, atmospheric oxygenation, Neoproterozoic, animal evolution
- MeSH terms
- Adaptation, Biological, Animals, Atmosphere, Base Sequence, Denmark, Biological Evolution, Kinetics, Molecular Sequence Data, Oxygen, Oxygen Consumption, Porifera, Polymorphism, Restriction Fragment Length, RNA, Ribosomal, 16S, Sequence Analysis, DNA, Microbiota
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