In an upcoming issue of Palaeogeography, Palaeoclimatology, Palaeoecology, an Elsevier journal on ... well, see title, two Polish palynologists will publish a paper entitled "Upper Eocene palynoflora from Łukowa (SE Poland) and its palaeoenvironmental context". It is a light microscopy study of the a fossil pollen assemblage, which – using the Coexistence Approach – allows estimating a "... mean annual temperature of 17.2–23.1 °C ..." Two years after we showed that the Coexistence Approach can never work (Grimm & Potts 2016).
The paper demonstrates that the editorial board of PPP remains ignorant of our critiques (see Postscriptum) and puts blind faith into very biased peers (leading members of the NECLIME syndicate) for their confidential (to third parties, at least) reviews. This 2018 study is just another case demonstrating the fundamental flaws of the Coexistence Approach outlined in Grimm & Potts (2016 [open access/discussion paper]) and Grimm et al. (2016) [open access pre-print/pay-to-access peer-reviewed version]. Arguments and results that stand unchallenged by Coexistence Approach practitioners. And a proof of case that peer review should be transparent and not confidential.
The study
From a general point of view, it's not a bad study. The pollen plates are nice, the quality of the fossil material seems to be very good. (I'm not a palynologist, hence, cannot say anything about the reliability of the determination, and association with modern-day genera and families). But, the authors describe just a single fossil pollen flora, and draw a lot of conclusions from their taxon list. So, one should have really used SEM imaging for the pollen, which- provides usually much more pollen morphs, and
- allows better identification of the pollen morphs.
Notably, the authors take a broader stand than found in core-NECLIME studies, which typically revolve entirely around the pseudo-quantitative results of the Coexistence Approach. Nonetheless, their abstract gives as main result "... a mean annual temperature of 17.2–23.1 °C."
"Mean annual temperature" refers to the yearly average temperature Tann in climate literature/databases, typically calculated as the arithmetic mean of the average monthly temperatures. The result does not say a lot, it points to a subtropical setting. The climate station data we used for our first validation paper (Grimm & Denk 2012; Northern Hemisphere only) includes 352 stations falling in this range (out of a total of 2625).
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| Climates at northern hemispheric climate stations with Tann between 17 and 23 °C. |
Worobiec and Gedl conclude (p. 11): "The presence of frequent pollen and spores of the genera growing now under tropical and subtropical climatic conditions and presence of several taxa characteristic for swamps indicate that the climate during deposition of the sediments studied was warm and humid." – well, according to their reconstruced intervals, we can fairly exclude a tropical setting (see pie chart). And "Nevertheless, the MAT estimated for the studied Łukowa seccion is in general agreement with other upper Eocene localities from central Europe." – MAT's estimated with the same flawed method, and published in NECLIME studies, all of which have obviously not been critically reviewed; and none of which documented any primary data.
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| The phenomenon of pseudocoexistence. The species cannot coexist, but would inform (pseudo-) precise "coexistence intervals" (Grimm & Potts 2016). |
But: We showed (and one of our papers is cited) that all well sampled fossil floras will inevitably converge on a humid subtropical climate as well as random samples. Because this is the climate all plants can thrive in, hence, theoretically can coexist. And pollen can be transported across large distances. What CA studies do for now more than two decades is to push trivial results by pseudo-quantitative estimates, while a) not documenting the used data and b) ignoring all sources of error and bias. Characteristics of a pseudo-science. The peer review should ensure that such is not published, but in the case of PPP it does exactly the opposite. It keeps a demonstrated, flawed method alive. It was an idea to pursue 20 years ago, but it was soon realised that it is too crude and too instable, and the CA-advocators have never tried to surpass even the most basic problems such as that climate niches are not rectangular and the need to discern between actual coexistence and pseudocoexistence (pollen can be transported over large distances).
What is the Coexistence Approach?
In short, an a-statistical actuo-palaeontological approach with many pseudo-scientific attributes when it comes to application, advocated by the NECLIME syndicate and published uncritically in PPP and a few other outlets with lower impact and confidential peer review. Studies in "big" journals are summaries that never deal with actual data, but just sum up results of primary publications, results published mostly in PPP facing little scrutiny during review and obviously unchecked by the peers working for the higher-ranking journals (otherwise they would note things like an alleged temperature gradient of 15 °C on Iceland during the Miocene based on "proxy data"). The likely reason for this do-whatever-you-want deal may be the over 10,000 citations (most within-syndicate), the Coexistence Approach generated for PPP since 1997, when the method was launched (Mosbrugger & Utescher 1997 in PPP; I'd love to see the original review reports). |
| Dissimination platforms of papers citing the original Coexistence Approach study Mosbrugger & Utescher (1997). Includes papers that just mention it, and a few negative citations that discussed it as flawed. CA-papers are a notable business for PPP (R-based analysis done end of 2014 by my co-author Alastair Potts using Web of Science literature database) |
The Coexistence Approach had a bumpy start: the first actual application paper was published in 1999, in PPP, naturally. In the same year the Tübinger Mikropaläontologische Arbeiten published a Ph.D. study supervised by Volker Mosbrugger showing that the Coexistence Approach performed worst of various tested alternatives (Klotz 1999). Mosbrugger was not only one of the two initiators of the Coexistence Approach but also of NECLIME (currently head of the famous Senckenberg institute and society). NECLIME is based on a simple deal: the Germans bring the money and the others the needed skills. The CA-results of Klotz were never re-published in an accessible journal, and it has been a common sport in the beginning to cite this thesis for the opposite (e.g. Bruch & Zhilin 2007 in the PPP-special issue, guest-edited by leading NECLIMErs).
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| The basic principle of unweighted mutual climate range approaches such as the Coexistence Approach (Grimm & Potts 2016). |
The reason for dropping more promising methods was that the coexistence approach is very simple to apply, you don't need any mathematical or computational skills, or a good data basis. A list of fossil taxa (here: mostly artificial pollen taxa used for stratigraphic purposes) is translated into a list of modern-day analogues, so-called 'nearest-living relatives'. A database providing minimum and maximum tolerances for those nearest-living relatives is then used to establish the "coexistence interval", the parameter overlap range (mutual climatic range) at which all or most of the nearest-living relatives can coexist.
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| How the Coexistence Approach works. A. Standard interval, the tolerance of all NLR have an overlap (this is a mutual clilmate range approach). B. The red and black have no overlap, the CA infers two possible intervals. C. The two red exotics eliminate the black NLR as "climatic outlier", the coexistence interval is very precise and unrepresentative for the flora. B and C do not fufil the requirements of an unweighted MCR (Grimm et al. 2016). |
- bursts out in laughter;
- insane-looking head shaking (western style, not eastern where it means yes, yes);
- comments the method using political incorrect, but scientifically correct language.
In most papers the nearest-living relative tolerances come from the still mostly obscure Palaeoflora Database, which has been much updated in the last years (according Utescher et al. 2014; no assessment/ evidence produced then or later); obviously following our "fundamentally flawed" (Utescher in Hoorn et al. 2012) [here's the full story], first critique (Denk Grimm 2012).
[Trivia: Torsten Utescher was a quite unsuccesful palynologist in Bonn (see his pre-1997 publication list) until he teamed up with Mosbrugger, and now acts as the Archmage of the Coexistence Approach. He's the man who knows how to use the FORTRAN programme that spills (still?) out the Coexistence Approach/Palaeoflora Database results. His skills are described by faithful NECLIMErs as unbelievable how much this man knows about climate and vegetation. For a proof, see the tolerance data provided in the intitial 1997 publication for the yearly average temperature (MAT), for more than a decade (Quan et al. 2012), the only CA/Palaeoflora study releasing primary data. Intervals that are all erroneous, to various degrees, and including many that were still used until very recently. The obviously all-knowing Utescher determined these (and later) tolerances by "... careful selection of 4–6 climate stations ..." (Utescher et al. 2014). See also this PDF, providing the sometimes very funny comments of the "anonymous reviewer #2", Utescher (obviously), to our paper published in 2012. Following the experience during the 2011 review phase – it took Utescher and his NECLIMinions more than six months to come up with reasons (all easily rebutted) to reject our paper – we published our 2016 application reality add-on (Grimm et al. 2016) as pre-print on bioRxiv (Grimm et al. 2015) and chose, over half-a-year later, an open review journal for the final theoretical paper (Grimm & Potts 2016). A game changer. Unfortunately, neither Archmage Utescher nor any other of the Faithful used the opportunity of an 8-week open discussion phase to comment, although I send all of them a mail inviting them to do so. They also refused to review the Grimm et al. (2016) paper. A fine example of scientific discourse, when one cannot hide behind the Impermeable Fog.]
In 2012 (well 2010/2011, actually), we looked at the CA/Palaeoflora "MAT" tolerances ("mean annual temperature", the average temperature across the year), the only freely accessible information at the time — you logged-in with a fake e-mail address such as asdf@stupid.com, search a taxon name (genus) and then copy & paste the information into a spread-sheet file. We showed that "MAT" tolerances can be nigh-erroneous, especially in case of nearest-living relatives crucial for published reconstructions. And the method cannot capture obvious climatic gradients. In his review of our 2012 paper, Utescher stated all our critique are naught because we overlooked that East Asian trees and bushes grow today outside their natural climatic niche [PDF of his review and our rebuttal] in the mountains of China. Implying that all fossil floras are low-land assemblages. So much for actuo-palaeontological approach, Utescher seems more to think of a palaeo-actualistic approach.
Related side note: As a new slap into the face of open data and minimum requirements regarding documentation of used data, you are now re-routed to the corresponding Pangaea site, a site to store and publish geological and palaeoclimatological data. I didn't try all the links, but wish you good luck to find what is promised on NECLIME's entry page (and in the various published papers referring to Pangaea or cited the Palaeoflora Database) and should be there: the used tolerance data for the reconstructions.
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| This is what you get when you click on "data base" in NECLIME's navigation bar these days. Earlier, you would choose "Search the Palaeoflora Database", and could access ("outdated", Utescher, in his 2012 review) "MAT" tolerances. For a short time access to other parameters was promised, but not provided. Now the link has been replaced by a link to the Pangaea site, where you find a lot of results but no primary data on the used climatic tolerances to get these results. Not documenting the data used to produce (and allowing to re-produce) results is another characteristic of pseudo-science. |
The main flaw of the Coexistence Approach (in this case)
Let alone the ridiculous insistence of Coexistence Approach papers like the fresh-from-the-press Polish paper to report pseudo-precise estimates such as 17.2–23.1 °C as main result (see their abstract). It is technically impossible to define bioclimatic brackets, tolerance intervals, with a precision of a tenth of a centigrade, something even Utescher et al. (2014) realised, while ignoring it in practise (e.g. Utescher et al. 2009 providing a fine-scale example; Quan et al. 2012, see Grimm et al. 2016 for the real results). And not meaningful to propagate them into the past; in the case of Worobiec & Gedl: some 35 Ma. Ironically, the Coexistence Approach or unweighted mutual climate range methods in general, performed worst already for the most-recent past, i.e. the Pleistocene (see Klotz 1999; Thompson et al. 2012) and when using realistic tolerance data.The ultimate most important problem of the Coexistence Approach, in theory (Grimm & Potts 2016) and practise (Grimm & Denk 2012; Grimm et al. 2016) is that the most exotic elements in a flora – the least tolerant taxon pair – define the reconstructed past climate. This is particular a problem, when these most exotic elements are relicts: Plant species/genera/families that today only occupy a very limited range, but were much more widespread in the past. Even the Masters of CA disencourage using such taxa. According protocol (e.g. Mosbrugger & Utescher 1997), but not practise (see all Coexistence Approach papers co-authored by Utescher).
[More trivia: You may find it interesting that there are only very relatively few Coexistence Approach papers co-authored only by Mosbrugger and not also by Utescher. One reason is that Utescher is the High Curator of the Palaeoflora Database. Another reason may be, that Mosbrugger knows that it is flawed, why he advised me in 1998 (!) to choose a phylogenetic topic for my Diplom thesis (Grimm, 1999, online version, in German) and not to enter the world of palaeoclimate reconstruction. Quote: "You are too intelligent for palaeoclimate research". Not sure about "too intelligent", but I am definitely too perceptive regarding data incoherence. Why I soon dealt in networks, not trees.]
In general, it is very risky to assume that the climatic niche hasn't changed, which we do when we decide on a yearly average temperature of 17–23 °C in the Eocene based on the range occupied by a two modern-day potential relatives.
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| Shifting climate niches: an inevitable problem of all nearest-living relative methods. The only solution is to find means to at least qualitatively assess this effect (see Grimm & Potts 2016, and literature cited therein). The Coexistence Approach solution to the problem is to ignore it. |
Naturally, it becomes riskier with every million of years we go back. However, this has never been a problem for authors, editors and likely NECLIME-affiliated "anonymous" peers of PPP, which published two special issues, guest-edited by leading NECLIMErs and likely reviewed internally (in order words: not at all). And it's trivial that you have no idea how the climatic niche looks like (not even roughly), when your nearest-living relative is the last surviving species of a once widespread lineage.
Which brings us to the paper of Worobiec & Gedl, and why it could only pass the peer review in a journal applying a strict non-transparency policy; for the peer review process and regarding data documentation.
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| The single-blind, confidential peer review process.Join #FightTheFog at change.org |
Eine Schwalbe macht noch keinen Sommer
A German saying: "One swallow does not indicate summer has come" (not a few of us are still waiting for winter's coming, could you please, J. R. R. Martin, before you die?) But in the Wonderous World of Coexistence Magic, one relict can (and will).In contrast to most NECLIME coexistence approach papers, Worobiec & Gedl show the bar chart for their main climate parameter, the yearly average temperature (called "mean annual temperature" "MAT" in Coexistence Approach literature), in their fig. 3 with a revealing title: "Attempt at an application of the Coexistence Approach method to the palynoflora studied" and a table of the bracketing nearest-living relatives in their table 3: "Results of palaeoclimate calculations with the Coexistence Approach and list of taxa defining the palaeoclimate coexistence intervals (lower and upper limit). No outliers." Attempt would have been also here the more fitting word, and a failed one.
The most critical fossil pollen taxon for three of the six parameters is Fususpollinites fusus. Worobiec and Gedl chose as nearest-living relative "Trigonobalanus s.l." following the Palaeoflora Database. A former genus within the beech tree family (quite a old stub on Wikipedia), the Fagaceae, that has been dissolved into three genera, Colombobalanus in Columbia, Formanodendron and Trigonobalanus in East Asia.
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| A synoptical time-scaled phylogenetic scheme for the Fagaceae, the beech tree family (Grímsson et al. 2016). Worobiec & Gedl's Fusupollinites is considered to form part of the trigonobalanoids; the Upper Eocene is highlighted by colour (cyan). |
All three genera comprise a single species and are limited in their geographic ranges; two are subtropical mid-altitude trees, Trigonobalanus goes into the Malayan tropics. Genetically, the split makes sense: the three species are very distinct and reflect an ancient (Paleocene or earlier) divergence within the Fagaceae, the beech tree family, that also includes the well-known oaks.
Let alone that no-one has ever published a decent distribution map of these three species, there is no doubt that they are unrepresentative relicts. Trigonobalanoid pollen is not only frequent but also widespread in the Palaeogene of the Northern Hemipshere, which fits to the branch-lengths seen in molecular trees. They are one of the pollen morphs you would expect to find in any properly studied Eocene, but also the substantially colder Oligocene, fossil flora in Europe.
Any reviewer, even those faithful to the Coexistence Approach, would have had to point out to the authors that this nearest-living relative has to be removed. But when you do this, and remove other relicts with equally dubious modern-day intervals, the coexistence intervals become too large to say anything. A classic problem of the Coexistence Approach: realistic tolerances and properly determined and assigned fossil taxa lead to scientific nirwana.
The documentation, i.e. the general lack of it
Another evidence that this paper was not critically reviewed, or properly done reviews were ignored by the editor, is the documentation. The authors report to have used three datasets of climatic tolerance data, which can be quite different. To demonstrate the utility of their method, Utescher et al. (2014) did not show any graph based on their data, the Palaeoflora Database, but a fraction of the much more reliable data of Thompson et al. (1999–2012a). Data, we used in our 2012 critique to proof the Palaeflora Database wrong and until then (or later) were never used (cited) by any paper published under NECLIME aegis (too large tolerances for many critical nearest-living relatives).Not requiring that the used tolerances are documented says a lot regarding scientific sincerity and quality of confidential peer review imposed by PPP. The method and primary data remains unvalidated and largely undocumented by the restricted CA community. Although we provided freely accessible check-up floral lists in our 2012 paper [8 MB/reduced 3 MB archive], which they could use to demonstrate the capacity of their method to capture different climate conditions. For North America, Thompson et al. (2012) did a test, and came to the conclusion that unweighted mutual climate range methods such as the Coexistence Approach are pretty useless. Guess how often this paper is cited in PPP publications promoting the Coexistence Approach published since then? Worobiec & Gedl claim to have used Thompson et al.'s tolerances and cite their 2015 atlas, but seem to have missed this important application test of that data.
Given the many "uncertainties" about the tolerance data (preferred terminology in Utescher et al., 2014, when addressing error sources), it would be obligatory to list the used tolerances, and not only the used nearest-living relatives (Worobiec & Gedl's table 1, a fine table compared to the standard of NECLIME-syndicate papers published in PPP). So, an informed reviewer could point out obvious deficits — you can't determine the modern-day tolerance with an accuracy and precision of 0.1 °C or mm of monthly precipitation; and the less obvious such as unrepresentative tolerance data. We outlined minimum necessary documentation already in our 2012 paper, and Utescher et al. (2014) took it up as their own idea (see Grimm et al. 2016, table 1). Needless to say, PPP did not ask any of us to review the 2014 paper of Utescher et al. as they were asked to review or comment on all of our method critiques. Clearly, we cannot be as objective as a NECLIME Inner Circle acolythe.
The beauty of confidential peer review: no-one can ask questions about the process. Everything that happened remained in the dark.
Another minimum requirement is to document the material, so informed reviewers may point you to misidentified or taxonomically problematic fossil taxa. Also in this respect, Worobiec & Gedl surpass by large the general poor quality of other Coexistence Papers published in PPP. They provide high-quality light-microscopy plates of their pollen taxa, a neccesary but very rare feat.
But one is missing: Fususpollinites fusus. Exactly the pollen that defines three lower boundaries of the coexistence intervals, yearly average temperature ("MAT"; >17.2°C), annual precipitation ("MAP": 1217–1724 mm), and "MPWet" (254–424 mm), the "mean precipitation of the wetter month" — whatever that means.
Ranges the Coexistence Approach always finds when more than 10, 15 nearest-living relatives are used, because they frame a climate situation beneficial for any plant taxon: comfy and wet, in other words humid subtropical (Universal coexistence — all roads lead to North Carolina in Grimm & Denk 2012, but Yunnan is likely, too in Grimm et al. 2016).
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| As expected. Worobiec & Gedl's "coexistence intervals" (red bars) compared to "center values", the mid-point of the "coexistence interval" of random subsamples of the tolerance data provided in Quan et al. (2012; Grimm et al. 2016). |
And either because they are really wary (a bit) of the methodological pitfalls, or one of the other reviewers pointed them to it, Worobiec & Gedl state (p.10 in the advance online version): "Taking into consideration the above mentioned remarks and the critical analysis of the Palaeoflora database and the Coexistence Approach for palaeoclimate reconstruction (Grimm et al., 2016; Zaborac-Reed and Leopold, 2016), we realise that this result is an estimation and represents an average value over various habitats and regional settings." — an euphemism, and wrong in essence. We showed that the Coexistence Approach cannot average over various habitats, but will always result in a subtropical humid setting, when elements of various habitats and climate zones are mixed (altitudinal gradients).
They proceed: "Nevertheless, climatic ranges of all taxa included in the analysis show overlapping. This means that a consistent reconstruction of the past climatic situation is obtained (cf. Utescher et al., 2014)" — No. It does not. Quite the opposite! If the climate ranges are not overlapping you know that your taxon list has a severe problem, a first-level error (the "uncertainties" in Mosbrugger & Utescher 1997 and Utescher et al. 2014). But overlap alone does not mean your tolerances are meaningful or do provide any support for the result of the coexistence interval. Only large, undecisive intervals give credibility to the reconstruction. We showed this, from a theorical point of view and using Quan et al.'s Palaeflora Database excerpt, whereas Utescher et al. (2014) just repeated the unproven 1997 claim that the percentage of potentially coexisting nearest-living relatives has any meaning.
How to avoid bad or fraudulent science
The study of Worobiec & Gedl demonstrate why the peer review must be transparent, following the example of PeerJ and a few other journals. In addition to Utescher, another reviewer, a real palynologist and junior co-author of Grimm et al. (2016), signed his report, and hangs with the deficits and errors in the published paper. I contacted him and he wrote me that he provided help and hints as best as he could, but what can you do if the authors ignore you and the editors back them. But the experience makes you re-consider whether you should accept any further invitation to review, since it's only done pro-forma. And, encourages you to fight the Impermeable Fog. Third parties should have the right to know what the reviewers said, and at least fathom how the editor decided. Otherwise the quality of a paper and its main results cannot be assessed by most of the reviewers.I have no access to the submitted version or the reviewer reports to assess the quality and objectivity of the peer review process, and cannot get any legal access to them. And even if I would have been a peer (God beware...), and the authors and editor would have ignored everything I pointed out because the Great Archmage Utescher feels otherwise, I cannot make this public because that would be breaking the sacro-sanct review confidentiality. And my research career would have a nasty stinch to deal with (Thank God, I'm not a scientist anymore!)
Pseudo-science like the Coexistence Approach can only thrive thanks to the shadiness of the confidential peer review. When exposed to the light of open scientific discourse, it crumbles to dust. And Coexistence Approach results should not be published until it has been assessed what they can show (see last section in Grimm & Potts 2016, added following the suggestion of one reviewer, Anonymous 2016, to give our paper a positive-constructive touch; or a reviewer collective, the last line in the report said "We recommend that the corrections should be reviewed").
The editors of PPP have proven in the past that they are reluctant to do anything against the CA-clique in their allegedly peer-reviewed journal, and put their heads in the sand whenever the Archmages of the Coexistence Approach pass through. The handling editor of these papers is not mentioned, hence, no-one has to take the responsibility for publishing pseudo-scientific results. But, the NECLIME syndicate produces just too much impact for the journal, too much for a mid-tier journal struggling to keep its impact factor > 2 to stop riding the dead horse (see Wisdom of the Dakota Tribe, in German).
As final consequence, a potentially good and informative paper disqualified itself scientifically. PPP's confidential peer review and documentation policy ensures that "estimates" (house numbers) of unknown quality pass as proper research. To use the magnificient words of a very intelligent man, maybe even more intelligent than Utescher, and surely more intelligent than me.
So sad!
Maybe, when The Donald is back to a normal life (and does not die in office, even his healthy orange skin colour starts to fade), PPP can hire him as the next Editor-in-Chief to #MaPaPaPaGA ... from fake news to fake science.
Postscriptum. Although I cannot do anything against the publication of CA studies like the one of Worobiec and Gedl, I'm on it, of course. Don Grimxote charges any windmill! E-mail has been sent yesterday afternoon, and my request to see the reports has been ignored so far. But one of the addressed editors, Thomas Algeo, replied promptly that he can "... not know whether [my] criticism of the Coexistence Approach method has validity." — interesting statement for an editor of the main dissimention platform of CA papers. But he is "... happy to entertain either (1) a Comment from [me] regarding a specific Palaeo-3 paper, or (2) a full-length research article in which [I] address the issue in a manner built around your own original research", which will go through "... the normal review process". In case of PPP, option (1) can mean that you submit a Comment, which is then ignored for six months by the editor and you get a nice e-mail afterwards informing you that now the reports are finally there, but unfortunately your reply cannot be considered anymore because it is too late to publish (needs to be done within six months). Option (2) ... well such papers are published, there is nothing to add.
I told Algeo, I'm happy to write a comment to Worobiec & Gedl, provided that
- the authors (playing dead so far) send me the tolerance data they used, and
- at least my review process will be made transparent.
References
Anonymous. 2016. Interactive Comment on "Fallacies and fantasies: the theoretical underpinnings of the Coexistence Approach for palaeoclimate reconstruction" by G. W. Grimm and A. Potts. Climates of the Past Discussions 11:C2884–C2888. www.clim-past-discuss.net/11/C2884/2016
Bruch AA, Zhilin SG. 2007. Early Miocene climate of Central Eurasia — Evidence from Aquitanian floras of Kazakhstan. Palaeogeography, Palaeoclimatology, Palaeoecology 248:32-48.
Grimm GW, Bouchal JM, Denk T, Potts AJ. 2015. Fables and foibles: a critical analysis of the Palaeoflora database and the Coexistence Approach for palaeoclimate reconstruction. bioRxiv doi:10.1101/016378. http://dx.doi.org/10.1101/016378
Grimm GW, Bouchal JM, Denk T, Potts AJ. 2016. Fables and foibles: a critical analysis of the Palaeoflora database and the Coexistence Approach for palaeoclimate reconstruction. Review of Palaeobotany and Palynology 233:216–235.
Grimm GW, Denk T. 2012. Reliability and resolution of the coexistence approach — A revalidation using modern-day data. Review of Palaeobotany and Palynology 172:33–47.
Grimm GW, Potts AJ. 2016. Fallacies and fantasies: the theoretical underpinnings of the Coexistence Approach for palaeoclimate reconstruction. Climates of the Past 12:611–622. http://www.clim-past.net/12/611/2016/cp-12-611-2016.html
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Mosbrugger V, Utescher T. 1997. The coexistence approach -- a method for quantitative reconstructions of Tertiary terrestrial palaeoclimate data using plant fossils. Palaeogeography, Palaeoclimatology, Palaeoecology 134:61-86.
Thompson RS, Anderson KH, Bartlein PJ. 1999–2001. Atlas of relations between climatic parameters and distribution of important trees and shrubs in North America — Hardwoods. U S Geological Survey Professional Paper 1650–A,B,C.
Thompson RS, Anderson KH, Strickland LE, Shafer SL, Pelltier RT, Bartlein PJ. 2006. Atlas of Relations Between Climatic Parameters and Distributions of Important Trees and Shrubs in North America—Alaska Species and Ecoregions. U S Geological Survey Professional Paper 1650-D:1-342.
Thompson RS, Anderson KH, Pelltier RT, Strickland LE, Bartlein PJ, Shafer SL. 2012a. Quantitative estimation of climatic parameters from vegetation data in North America by the mutual climatic range technique. Quaternary Science Reviews 51:18–39.
Thompson RS, Anderson KH, Pelltier RT, Strickland LE, Shafer SL, Bartlein PJ. 2012b. Atlas of relations between climatic parameters and distributions of important trees and shrubs in North America—modern data for climatic estimation from vegetation inventories. U S Geological Survey Professional Paper 1650-F. http://pubs.usgs.gov/pp/p1650-f/
Utescher T, Ivanov D, Harzhauser M, Bozukov V, Ashraf AR, Rolf C, Urbat M, Mosbrugger V. 2009. Cyclic climate and vegetation change in the late Miocene of Western Bulgaria. Palaeogeography, Palaeoclimatology, Palaeoecology 272:99-114.
Utescher T, Bruch AA, Erdei B, François I, Ivanov D, Jacques FMB, Kern AK, Liu Y-SC, Mosbrugger V, Spicer RA. 2014. The Coexistence Approach—Theoretical background and practical considerations of using plant fossils for climate quantification. Palaeogeography, Palaeoclimatology, Palaeoecology 410:58–73.
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