the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Sep 2026
A Paleoclimate Proxy from Ammonite Suture Line Complexity
Abstract. Changes in atmospheric composition, driven by fluctuating concentrations of greenhouse gases, are the primary driver of climate change, alongside variations in oceanic circulation. Reconstructions of temperature and climate over geological timescales rely on qualitative and quantitative proxies preserved in the geological record. Sedimentary deposits such as coal, evaporites, bauxites, and tillites, although they represent specific climatic regimes, have low temporal resolution. By contrast, quantitative geochemical proxies such as δ18O or δ13C, clumped-isotope thermometry, TEX86, and Sclerochronology offer higher temporal resolution. However, these proxies have limitations, reflecting, in some cases, local post-depositional variation or alteration, indicating a need to integrate proxy methods to establish reliable and robust paleoclimate reconstructions.
In this paper, we present a new qualitative method for reconstructing temperature, based on the fractal dimension of ammonite suture lines, which can integrate with and support well-established paleoclimate proxies. Suture lines mark the contact between the septum, formed by the organism, and its shell. The linear pattern of fossil sutures exhibits a fractal dimension and resembles viscous fingering—a process that depends on fluid viscosity. Based on the fractal dimension of c. 450 taxa of Cretaceous ammonite sutures (143–66 million years ago), we present a fractal dimension curve that serves as a qualitative proxy for seawater viscosity and inversely correlates with seawater temperature. The curve reveals warm and cold snaps associated with geological events that may have triggered climate changes during the Cretaceous, such as Large Igneous Provinces, seafloor production, mid-ocean ridge length, and Oceanic Anoxic Events.
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Status: open (until 23 Nov 2026)
- CC1: 'Comment on egusphere-2026-5429', Giacomo Medici, 30 Sep 2026 reply
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CC2: 'Comment on egusphere-2026-5429', Katherine Marriott, 02 Oct 2026
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This preprint claims to present "a new qualitative method for reconstructing temperature, based on the fractal dimension of ammonite suture lines, which can integrate with and support well-established paleoclimate proxies."
This claim of novelty is factually incorrect and ignores direct, documented prior works of mine dating 2024-2026, including my own documented work published within EGU spaces.
While the authors cite my earlier paper on partial suture normalizations (Marriott & Chamberlain, 2021), which is only tangentially related to this specific topic, they have omitted my subsequent research and public disclosures that explicitly established, tested, and presented ammonite suture fractal complexity as a paleoclimate proxy. Most egregiously, this includes work published on this exact platform earlier this year.
This preprint cannot claim that using ammonite suture complexity as a paleoclimate proxy is a novel finding. I was under the impression that my research was recognized and respected when I presented work with almost this exact title and premise earlier this year. Citations establishing that this is not an original discovery by the authors, but rather an ongoing line of research from my own lab, include:
- Marriott, K. (2026). Ammonite suture complexity as a paleoclimate indicator comparable to δ18O stable isotope ratios. EGU General Assembly 2026, Vienna, Austria, EGU26-4310, https://doi.org/10.5194/egusphere-egu26-4310.
- Marriott, K. (2024). Bigger on the inside: South Pole Maastrichtian ammonites and Bergmann’s Rule. Geological Society of America Connects 2024, Anaheim, CA.
- My website https://www.suturelab.org/ which has this exact topic posted as an active project and has for months.
Selectively citing my older 2021 methodology while ignoring my published EGU presentation on the exact same subject, on this exact platform where I presented this topic months ago, s unacceptable. The handling editor must require the authors to remove claims of novelty and properly credit my prior art and precedence before this manuscript is considered further for Biogeosciences.
For the record,
Kate LoMedico MarriottCitation: https://doi.org/10.5194/egusphere-2026-5429-CC2 -
CC3: 'Reply on CC2', Katherine Marriott, 02 Oct 2026
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An addendum to my previous comment: I don't believe the sociopolitical environment of the geosciences field can look at this in a vacuum. I strongly encourage the authors and handling editors to reflect on this dynamic, specifically the Matilda Effect (Rossiter, 1993), by which major breakthroughs by early-career female scientists are published as "novel discoveries" by men, and to ensure that the citational practices in Biogeosciences uphold equitable attribution for public, date-stamped contributions across all EGU forums. My hope is that what has happened so often throughout scientific history will not be allowed to happen here.
Citation: https://doi.org/10.5194/egusphere-2026-5429-CC3 -
AC1: 'Reply on CC2', Pierpaolo Guarnieri, 02 Oct 2026
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Dear Katherine,
I'm positively surprised to read that other scientists are working on a similar topic to the one presented here. On the other hand, I have to say that our paper was submitted for the first time (basically with the same structure) in October 2025 to other journals (I can document this if needed), and after being rejected a few times, we ended up submitting it to Biogeosciences in September 2026. That means we started well before your abstract at EGU26 was published, which we didn't know existed. This was the reason for claiming the novelty of our paper. You also refer to another abstract from 2024. I have to say that, as a general rule, most of the journals do not recommend referring to abstracts as references when submitting a manuscript. Abstracts are not peer-reviewed, and they may not end up in full publication. We do refer to one of your published papers (Marriott and Chamberlain 2021) not because of selective citing but because of the dataset that is included with it.
I hope my answer clarifies the issue.
Best regards,
Pierpaolo
Citation: https://doi.org/10.5194/egusphere-2026-5429-AC1 -
CC4: 'Reply on AC1', Katherine Marriott, 02 Oct 2026
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Dr. Guarnieri,Several points here require additional clarification for the public record, the reviewers, and the handling editor.
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Private submission timelines do not supersede public disclosures. A history of private submissions and rejections to other journals does not establish scientific priority over date-stamped disclosures. Scientific priority in the community is governed by what is placed on public record.Even if that were not true, the first time anyone mentioned that ammonite sutures change in response to temperature was in my researach in 2024—Marriott, K., et al. (2024) Bigger on the inside: south pole Maastrichtian ammonites and Bergmann's rule—Geological Society of America Connects 2024, Anaheim, California.Additional presentation of these concepts were at the Tate conference in Casper WY in June 2025: Marriott, K et al. (2025) "Adaptive radiation and Bergmann's rule in ammonite faunas across the Campanian -Maastrichtian Boundary, James Ross Island and Seymour Island, Antarctica"I presented this paleoclimate proxy as a novel discovery in 2024 and expanded upon it at EGU 2026. I conducted exhaustive literature searches to ensure this exact concept had never previously appeared in published record, and it had not. Claiminbg that an idea is "novel" in late 2026 without searching recent proceedings within EGU itself overlooks the established prior art.
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Conference disclosures establish prior art regarding claims of novelty. While peer-reviewed full manuscripts provide the complete empirical dataset, citable, DOI-indexed conference abstracts and presentations are universally recognized across the geosciences as establishing prior art. An author cannot claim that a proxy or theoretical concept is an original discovery when date-stamped and archived on this very platform (EGU26-4310). Copernicus itself assigns DOIs to EGU General Assembly abstracts precisely so they can be cited and recognized as formal scientific contributions (my GSA abstract from 2024, which predates your paper, was indexed as Abstract 165-3 for your records).
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Data utilization and citational context matters here. You acknowledge that you used the dataset from Marriott and Chamberlain (2021), which underscores the direct intellectual and methodological lineage from my work to your current preprint. Utilizing our published sutural complexity metrics while dismissing our more recent, directly related public disclosures as the first to describe this paleoclimate proxy is selective contextualization.
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Additionally, you cite a flawed mechanism of septal organogenesis which is largely considered outdated. In what is considered now foundational literature on ammonoid paleobiology, Klug and Hoffmann (2015) rejected the viscous fingering model of suture formation; this was corroborated in 2016 by Inoue and Kondo, which is widely considered the best explanation today for organogenesis. Building an empirical paleoclimate proximity on a physical mechanism of genesis that ammonoid workers widely no longer accept introduces an additional vulnerability to the manuscript.
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Notably absent from your response is any engagement with the ethical concern I raised regarding the Matilda Effect (Rossiter, 1993). In the geosciences, there is a pervasive, documented history of credentialed PhD-holding serior male researechers taking the intellectual breakthroughs of early-career women, particularly independent scholars and pre-doctoral women without secure institutional umbrellas, subsuming them as "novel discoveries" while relegating the true originator to a technical citation that has little if anything to do with the discovery itself. Famous examples of women being obscured from their own discoveries include Mary Anning, Rosalind Franklin, and most recently, paleontologist Melanie During. Please be aware that I have no issue disputing your actions to the extent that During had to.
To the editors, the issue I present is straightforward: this preprint claims that fractal complexity of ammonite sutures as a paleoclimate proxy is a novel discovery, but it was already indicated as such by me in an indexed abstract in 2024.Citation: https://doi.org/10.5194/egusphere-2026-5429-CC4 -
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CC5: 'Reply on AC1', Oryx Stormlance, 02 Oct 2026
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Pierpaolo,
Your response does not resolve Kate’s objection. It sidesteps it.
Your manuscript repeatedly claims novelty. The abstract presents a “new qualitative method for reconstructing temperature, based on the fractal dimension of ammonite suture lines,” the Introduction describes a “novel approach,” and the Conclusion calls it a “new qualitative non-isotopic paleoclimate proxy.”
By the time this manuscript was submitted to Biogeosciences on 7 September 2026, that application was already publicly documented by Marriott.
Marriott’s 2026 DOI-bearing EGU/Copernicus contribution, Ammonite suture complexity as a paleoclimate indicator comparable to δ18O stable isotope ratios, explicitly presents ammonite suture fractal complexity as a palaeoclimate indicator and compares it with δ18O.
The overlap is direct. Your manuscript uses ammonite suture fractal dimension as a palaeotemperature/palaeoclimate proxy and explicitly compares the resulting record with δ18O, TEX86 and other palaeotemperature records. This is not simply another researcher working on a “similar topic”, it is prior public work addressing the specific scientific application for which your manuscript claims novelty.
Your manuscript also explicitly incorporates published fractal-dimension data from Marriott & Chamberlain (2021) into its dataset of approximately 450 measurements. You were therefore demonstrably familiar with Marriott’s published work on ammonite sutural complexity. Yet her subsequent 2026 work addressing the palaeoclimate application now being claimed as novel is absent from your references.
Your October 2025 submission does not resolve this. A private submission to another journal does not freeze the scientific literature at that date. Whatever the development history of your manuscript, Marriott’s directly relevant work was publicly documented before your September 2026 Biogeosciences submission.
Nor does dismissing it as a conference abstract resolve the issue. Marriott’s contribution is a public, date-stamped, DOI-bearing Copernicus record. Whether journals generally prefer peer-reviewed articles over conference abstracts does not erase prior public work when assessing a claim of novelty.
The issue is therefore straightforward:
By 7 September 2026, the use of ammonite suture fractal complexity as a palaeotemperature/palaeoclimate indicator had already been publicly documented. The manuscript cannot accurately present that application as though it is being introduced for the first time.
Therefore, the handling editor must require the authors to remove or correct these claims of novelty, properly cite and discuss Marriott’s 2026 work, and recognise Marriott’s documented prior work and precedence before this manuscript is considered further for publication in Biogeosciences.
This is not a request to debate who privately conceived the idea first. It is about accurately representing the existing scientific record.
On that record, your claim of novelty does not stand.
Citation: https://doi.org/10.5194/egusphere-2026-5429-CC5
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CC4: 'Reply on AC1', Katherine Marriott, 02 Oct 2026
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CC6: 'Comment on egusphere-2026-5429', Rene Hoffmann, 09 Oct 2026
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In their EGUsphere article the author team around Pierpaolo Guarnieri describe a palaeotemperature proxy derived from ammonite suture line complexity. This is indeed an interesting approach potentially providing an independent morphological proxy for palaeotemperature changes – at least for the Jurassic and Cretaceous. Careful reading of the full article, however, raises some questions that need clarification before publication.
- It is not stated if the authors assume that water temperature, which directly affects water viscosity, also directly affects suture line complexity. If this is the case, it should be clearly stated and maybe demonstrated with an example of a relatively widely distributed species covering warm and cold water masses with respective difference in their suture line complexity at similar or identical whorl height. Then, however, it also needs to be pointed out that ammonites are regarded as vertical migrants analoguous to extant Nautilus and could have underwent daily vertical migrations of up to 300 m or more, which would also result in different water temperatures/viscosity.
- It is not clear from which ontogenetic stage the data for suture line complexity have been collected. Juveniles have a less complex suture line when compared to adults. Here I would expect a proper documentation, e. g., the respective shell diameter,whorl height, or ontogenetic stage. In this regard, the authors also mention the evolutionary trend from simple to more complex suture lines, which is not fully true. When looking at time intervals of major extinctions, ammonoids with simple suture lines survived. During the following recovery phase ammonites iteratively developed more complex sutures.
- Changes in suture line complexity have also been described by Bayer & McGhee (1984) in concert with changes of whorl cross section – both changed during changes of sea level.
- Some modern cephalopods retained a chambered shell: Nautilus with an external shell, like ammonoids, and sepiids or Spirula with an internal shell. None of these show such complexly folded septa, although their septal formation mechanism remains largely unchanged. As all cephalopods are ectotherms, the septa of nautilids and coleoids should be affected by temperature/viscosity as well (Klug et al. 2008, Klug & Hoffmann 2015). Palaeozoic cephalopods also never developed such complex folded septa but gave rise to the coleoids and ammonoids via the bactritoids (also with simple septal morphology). Specifically, within ammonoids I see no reason why the septal formation mechanism should change to being more dependent on water viscosity. Even more interesting is the re-occurrence of Cretaceous ammonites with simplified sutures, e.g., These occurred during the Coniacian in France, Spain, central Europe and northern and western Africa – a time of medium temperature (= no cold or warm snap) – and were sympatric with ammonites with complex sutures. How can this be explained if water temperature is the main driver for suture line complexity?
- Regarding the author’s favored explanation for the development of complex sutures, how can they rule out all other mechanical or physiological functions as potential drivers? None of these were discussed in detail.
- The septal formation mechanism for Nautilus has been described in detail by Klug et al. (2008) and at least three formation mechanisms were discussed by Klug and Hoffmann (2015) for ammonoids. These references were neglected by the authors, leaving the impression that only the viscous fingering model can explain septal formation. In addition, Seilacher´s (1973) tie point model or Hammers (1999) reaction diffusion model need to be mentioned/discussed. Based on their review on septal formation Klug and Hoffmann (2015) developed a composite model for septal formation that was, as far as we know, not rejected by any of the ammonite workers. According to this the septal mantle was fixed to the inner surface of the conch tube at the lobes and lobules first and became eventually fixed along the entire suture line. There are also muscles present in the mantle that could shape this outline. Development of septal shape is controlled by the whorl cross-section and its ontogenetic modifications (allometry); apparently, the phylogenetic increase in coiling of the initial whorls (De Baets et al. 2012) contributed much to the increase in sutural complexity. Additionally, a whorl cross section with narrow and wider parts (compressed or depressed whorl section) from early stages in ontogeny onwards made sutural complexity increase faster than in forms with simple subcircular cross sections.
- Viscous fingering model: This model is based on Hele-Shaw cells, however, the ammonoid shell resembles a tube - introducing another degree of complexity. The viscous fingering model fails to explain the (rare) disappearances of major lobes, e.g., the sixth lobe during early ontogeny of Late Cretaceous lytoceratids. The Viscous Fingering Model helps to understand how septum-like shapes with
their fractal aspect formed including the complexity of the suture and the shape of the septal surface in space. The Tie-Point Model postulates that muscles held the septal membrane in place, where the lobes formed, and that saddles are put in place by simple physical processes. It appears plausible that the preseptal membrane/septal mantle attached in the main lobules first and the control over the regular placing of lobules involved largely self-generating morphogenetic processes (Seilacher 1973, 1975; Westermann 1975; García-Ruiz et al. 1990; García-Ruiz and Checa 1993; Hammer 1999). The authors provide minimum and maximum complexity values of 450 ammonite suture lines. As proof of concept, it would be most interesting to use seawater of different temperatures (covering the potential upper and lower limits ammonites could have lived in (e.g., Nautilus does not survive in waters warmer than 27 °C) for Hele shaw cell experiments. Last but not least, it is also important to mention that the fluid that is in contact with the mantle tissue of the ammonoid is not seawater but a modified bodyfluid with potentially different viscosity (see e.g. Immenhauser et al. 2016).
Regards René
Citation: https://doi.org/10.5194/egusphere-2026-5429-CC6 -
CEC1: 'Comment on egusphere-2026-5429', Paul Stoy, 16 Oct 2026
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The BG co-Editors-in-Chief wanted to make a brief note regarding the present discussion.BG guidance (https://www.biogeosciences.net/submission.html#references) states the following:'Informal or so-called "grey" literature may only be referred to if there is no alternative from the formal literature. Works cited in a published manuscript should be published already, accepted for publication, or available as a preprint with a DOI.’The reason for this is that gray literature, including conference proceedings, has not undergone a normal peer-review process. These sources do not have the necessary methods information to reproduce results, or the underlying data to refute a claim or reject a hypothesis.However, the emergence of the EGUSphere preprint server notes the following regarding EGU conference abstracts (https://meetingorganizer.copernicus.org/EGU26/EGU26-3506.html?_=1778223849):'Conference material presented at EGU meetings can be publicly discussed by the scientific community beyond the meetings. All conference abstracts are fully citable with a unique digital object identifier (DOI) and can be amended by additional presentation material pertinent to EGU meetings’We hope that the open discussion nature of EGUSphere helps create a constructive resolution.Sincerely,Paul Stoy on behalf of the BG co-EiCsCitation: https://doi.org/
10.5194/egusphere-2026-5429-CEC1
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General comments
This is a very good pleao-research! Please, follow my comments to improve the final version.
Specific comments
Lines 36-38. “The qualitative lithological proxies include sedimentary deposits such as coal, evaporites, bauxite, and tillites that form under conditions characteristic of specific climate regimes or environmental settings”. Paleokartic intervals also reflect changes of the climate recorded in the sedimentary record. Please, integrate this point, and insert relevant literature below:
- Medici, G., Marianelli, D., Cornacchia, I., Gori, F., Brandano, M. 2026. Multi-disciplinary approach to paleokarst occurrence in the Eocene–Oligocene succession of the Apulia Carbonate Platform (Salento, Italy). Facies, 72(2), 17.
- Dan, Y., Lin, L., Liang, B., Zhang, Q., Cao, J., Li, J. 2019. Geochemistry of the fracture-cave calcite of the Ordovician Yingshan Formation and its paleokarst environment in the Tazhong area, Tarim Basin, China. Carbonates and Evaporites, 34(4), 1511-1524.
Line 68. Describe the specific objectives of your research by using numbers (e.g., i, ii, and iii) at the end of the introduction.
Line 175. Expand the result section which is too short.
Line 255. Expand the conclusions. This section is too short.
Line 255. Highlight the novelty of your research in the conclusions.
Line 255. End this section with a “take home” message for the audience.
Figures and tables
Figure 2. Insert a spatial scale for the samples.
Figure 3a. You need a spatial scale also here.
Figure 3b, c. Insert a spatial scale for the two conceptual models.
Figure 6. Numbers and labels are not readable on the vertical axis. Please, fix the issue.
Figure 7. This figure is unclear. Please, revise details on the two axes.