23-7 Changing ecological stability and community structure across Devonian biocrises in polar marine communities of the Paraná Basin, southeast Brazil

Session: Phylogenetic and Computational Approaches in Paleobiology and Paleoecology, Part I

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Abstract:

Most studies of changes in community ecology and trophic structures across ancient biocrises relate to tropical ecosystems, whereas polar systems are understudied. To fill this gap, we investigated how shallow marine communities in the Paraná Basin of Brazil responded to a set of biocrises in the Early to Middle Devonian using network analysis approach to explore ecological shifts in response to major environmental changes, such as salinity, sea-level, and basinal connectivity.

During the Devonian, the Paraná Basin was part of Western Gondwana and located at high-latitude (70°-80°S). Sedimentary units record siliciclastic, delta-influenced offshore to shoreface environments. The Early Devonian Paraná Basin fauna comprised mainly of native taxa and immigrant Malvinoxhosan species, whereas Malvinoxhosan taxa went extinct by the Middle Devonian. Two Early Devonian biocrises, the Zlíchov and Daleje, have been identified and correspond to episodes of marine regression and freshwater influx. The third biocrisis, the Middle Devonian Kačák event, correlates with a global transgression coupled with widespread anoxia associated with local extinctions.

We reconstructed ancient food webs for Paraná Basin marine communities to assess the severity of each successive biocrisis on community stability and structural changes. Species occurrence data were collected from bed-by-bed field observations and augmented with literature and scientific collection records. Occurrences were separated into four mega-communities representing four time slices, each separated by a biocrisis: Pragian-Emsian, late Emsian-Eifelian, Eifelian, and Givetian. We specifically applied combinatorial probabilistic models to reconstruct ancient food webs and community disruption through Cascading Extinction Graphs (CEGs) to develop a holistic reconstruction of community dynamics. Functional composition, trophic space, network structure, and paleocommunity dynamics were assessed for each mega-community. Primary results recovered that as species richness declined, community stability and trophic complexity declined after each biocrisis. These findings are consistent with previous studies on species richness for the Devonian of the Basin and are associated with the decline of the Malvinoxhosan fauna. However, this is the first time biodiversity loss has been studied under a community dynamics framework in the Paraná Basin. The incorporation of combinatorial network models into paleocommunities is essential for understanding the impacts of biocrises on community dynamics and species diversification.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7146

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