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| The illustration depicts a stable, warm-climate freshwater ecosystem as reconstructed from the ecological signatures preserved in ‘Viviparus’ sp. fossils. Centrally featured is the ovoviviparous reproductive strategy of these gastropods, with maternal individuals sheltering developing embryos and free-living juveniles. the Kitadani Formation (Tetori Group, Lower Cretaceous) based on integrated ecomorphological and taphonomic data. in Yoshimura, Nakayama, Asato, ... et Sasaki, 2026. Palaeoenvironmental reconstruction by Kohei Futaka. |
Abstract
Direct empirical evidence regarding the reproductive biology and trophic strategies of ancient freshwater invertebrates remains scarce due to the typical loss of internal anatomical and dietary records. Here, we report an exceptionally preserved assemblage of the freshwater snail ‘Viviparus’ sp. from the Lower Cretaceous (c. 120 Ma) Kitadani Formation, central Japan. High-resolution X-ray micro-computed tomography and microfossil extraction reveal key ecological adaptations: obligate ovoviviparity with up to 16 embryonic shells showing an axial developmental size gradient within the maternal body whorl, female-biased sexual size dimorphism, and continuous indeterminate growth. Analyses of gastrointestinal residues and taphonomic associations further indicate trophic flexibility (epilithic microalgal grazing, suspension feeding, and detritivory) alongside opportunistic microhabitat use within articulated unionid bivalves. This high-fidelity preservation—retaining delicate embryonic shells, intact protoconchs, and organic residues—is linked to a distinctive taphonomic window, wherein alkaline ash from palaeo-wildfires is inferred to have buffered ambient freshwater acidity, mitigating post-mortem carbonate dissolution. Our findings demonstrate that modern-type viviparid reproductive and feeding adaptations were already established by the Early Cretaceous, illustrating how wildfire-mediated geochemical buffering can preserve rare biological records in Mesozoic limnic ecosystems.
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| Palaeoenvironmental reconstruction of the Kitadani Formation (Tetori Group, Lower Cretaceous) based on integrated ecomorphological and taphonomic data. The illustration depicts a stable, warm-climate freshwater ecosystem as reconstructed from the ecological signatures preserved in ‘Viviparus’ sp. fossils. Centrally featured is the ovoviviparous reproductive strategy of these gastropods, with maternal individuals sheltering developing embryos and free-living juveniles. In the foreground, juveniles are shown utilising the empty articulated valves of the bivalve Plicatounio naktongensis Kobayashi & Suzuki (1936) as cryptic habitats or feeding grounds, providing evidence for opportunistic necrophagy. The background highlights a palaeo-wildfire event; the subsequent influx of alkaline-rich charcoal and ash into the aquatic system is proposed to have buffered the water pH, facilitating the exceptional preservation of delicate calcareous structures and internal organic debris. The high population density and continuous breeding of these viviparids, alongside contemporaneous vertebrate fauna such as iguanodontids, characterise a productive and resilient riparian landscape during the Early Cretaceous. Artwork by Kohei Futaka. |
Taro Yoshimura, Kentaro Nakayama, Kaito Asato, Yoshikazu Noda, Hiroyuki Fujimoto, Yuki Nakagawa, Julien Legrand, Masayuki Ikeda and Takenori Sasaki. 2026. Exceptional Preservation reveals the Deep-time Reproductive Ecology and Trophic Breadth of Early Cretaceous viviparid gastropods. Communications Biology. 9: 1450. DOI: doi.org/10.1038/s42003-026-11188-7 [10 November 2026]
