Abstract
Ants (Hymenoptera: Formicidae) are key ecosystem engineers in modern terrestrial environments, where their communities are structured by competition, niche partitioning, and dominance hierarchies. Whether such complex organisation existed deep in geological time remains unclear due to the rarity of direct fossil evidence for species co-occurrence. Here, we analyze eusyninclusions — fossilized assemblages comprising several ant species preserved together within individual pieces of Baltic amber from the late Eocene (~ 34–38 Ma). Among 3246 fossil ant specimens examined, we identify 110 eusyninclusions. Eocene ant assemblages show a strong prevalence of negative co-occurrence patterns, indicating non-random, competitively structured communities consistent with a deep-time ant mosaic. Two dominant species, †Ctenobethylus goepperti (Mayr, 1868) and †Lasius schiefferdeckeri Mayr, 1868, anchor distinct interaction clusters reflecting divergent ecological strategies. †C. goepperti exhibits low interspecific co-occurrence and high dominance, consistent with a territorial arboreal lifestyle, whereas †L. schiefferdeckeri displays frequent associations and a broader ecological tolerance, indicating a eurytopic subordinate role. Our results provide the first empirical evidence that ant mosaic–like community organisation was already established in the Eocene. These results highlight the deep evolutionary roots of ant community organisation and underscore the importance of preserving habitat structural complexity in the face of modern global warming.
Data availability
The empirical data and codes for the study are uploaded in Zenodo and can be accessed https://doi.org/10.5281/zenodo.18379116.
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Acknowledgements
We used Perplexity AI as a tool for generating the background image in Figure 4.
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This work was supported by Saint Petersburg State University, Project No. 132392751.
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Conceptualization: D.M.Z., D.A.D., V.M.K., E.V.A. Methodology: D.M.Z., D.A.D., V.M.K. Software: D.M.Z., V.M.K. Validation: D.M.Z., D.A.D., V.M.K., E.V.A. Formal analysis: D.M.Z., D.A.D. Investigation: D.M.Z., D.A.D., V.M.K., E.V.A. Data curation: D.M.Z., D.A.D. Writing— original draft: D.M.Z., D.A.D., V.M.K. Writing—review and editing: D.M.Z., D.A.D., V.M.K., E.V.A. Visualization: D.M.Z., D.A.D., V.M.K. Supervision: D.A.D., E.V.A. Project administration: D.M.Z., D.A.D., E.V.A.
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Zharkov, D.M., Dubovikoff, D.A., Khaitov, V.M. et al. Syninclusions reveal “ant mosaic” in the Eocene amber forest. Sci Rep (2026). https://doi.org/10.1038/s41598-026-44622-1
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DOI: https://doi.org/10.1038/s41598-026-44622-1
