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Published September 2022 | Published + Supplemental Material
Journal Article Open

Fossil Biomarkers and Biosignatures Preserved in Coprolites Reveal Carnivorous Diets in the Carboniferous Mazon Creek Ecosystem

Abstract

The reconstruction of ancient trophic networks is pivotal to our understanding of ecosystem function and change through time. However, inferring dietary relationships in enigmatic ecosystems dominated by organisms without modern analogues, such as the Carboniferous Mazon Creek fauna, has previously been considered challenging: preserved coprolites often do not retain sufficient morphology to identify the dietary composition. Here, we analysed n = 3 Mazon Creek coprolites in concretions for dietary signals in preserved biomarkers, stable carbon isotope data, and macromolecular composition. Cholesteroids, metazoan markers of cholesterol, show an increased abundance in the sampled coprolites (86 to 99% of the total steranes) compared to the surrounding sediment, indicating an endogenous nature of preserved organics. Presence of unaltered 5α-cholestan-3β-ol and coprostanol underline the exceptional molecular preservation of the coprolites, and reveal a carnivorous diet for the coprolite producer. Statistical analyses of in situ Raman spectra targeting coprolite carbonaceous remains support a metazoan affinity of the digested fossil remains, and suggest a high trophic level for the coprolite producer. These currently oldest, intact dietary stanols, combined with exquisitely preserved macromolecular biosignatures in Carboniferous fossils offer a novel source of trophic information. Molecular and biosignature preservation is facilitated by rapid sedimentary encapsulation of the coprolites within days to months after egestion.

Additional Information

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). We thank Peter Hopper, Alex Holman and Janet Hope for their technical support with GC-MS and stable isotope analyses. Tripp thanks Curtin University for a Research Training Postgraduate award, The Australian Institute of Nuclear Science and Engineering for an AINSE Postgraduate Research Award and support from The Institute for Geoscience Research for Star-fish Soxhlet extraction apparatus. Part of this research was undertaken using the XRD instrumentation at the John de Laeter Centre, Curtin University. Tripp thanks Veronica Avery and Matthew Rowles for technical assistance with XRD analysis. We thank Scott Lidgard (Field Museum, Chicago) for providing samples. We thank the three anonymous reviewers for their constructive comments that helped improve this manuscript. This research was funded by Australian Research Council (ARC) for an ARC-Laureate Fellowship grant (FL210100103) and ARC infrastructure grants (LE110100119; LE100100041; LE0882836; LE0668345; LE0775551). Author Contributions. M.T. and K.G. designed the experiments and overall project concept. M.T. performed all laboratory on the fossil concretions except Raman microspectroscopy and GC-MRM. J.W. performed Raman microspectroscopy and J.B. performed GC-MRM. M.T. wrote the manuscript with contributions from all co-authors. K.G. supervised PhD scholar M.T. and P.M. provided Mazon Creek samples and hosted K.G. and M.T. at The Field Museum for this study. L.S. contributed with interpretive work and written contributions. All authors have read and agreed to the published version of the manuscript. Data Availability Statement. Source data for ChemoSpace analyses (Figure 4 and Figure 5) are available in the Supplementary Materials. All other data can be made available upon request from corresponding authors. The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Additional details

Created:
August 22, 2023
Modified:
October 24, 2023