Detailed taxonomy and morphological analyses of two key ostracod species from Patagonia, Argentina: distribution and implications for paleoenvironmental reconstructions

Limnocythere rionegroensis and Limnocythere patagonica are among the most widely distributed ostracod species in Patagonia, Argentina, and are commonly used as proxies in paleoenvironmental reconstructions. Despite their relevance, a taxonomic revision was necessary due to the lack of detailed morphological descriptions. Here, we provide the first comprehensive anatomical characterization of the soft parts of both species. Our findings also underscore the diagnostic value of female genital morphology for ostracod species identification. We evaluate intra- and interspecific morphological variability across multiple populations, documenting size variation in both species and ornamentation differences in L. rionegroensis. Morphometric and anatomical analyses confirm that these variations fall within the range of intraspecific variability. We also explore the environmental preferences, geographic distributions, and significance of these taxa as climate indicators. Both species exhibit broad distributions across northern and southern Patagonia. Although they rarely co-occur in modern or recent assemblages, they are frequently found together in the sedimentary record, suggesting that limited coexistence may result from narrow environmental tolerances rather than geographic isolation. Our results clarify the taxonomic status and ensure the nomenclatural stability of both species. By integrating taxonomic, morphometric, environmental, and geographic data from numerous populations, this study improves the accuracy and reliability of paleoenvironmental reconstructions in Patagonia—a key region for understanding Holocene climate dynamics in the Southern Hemisphere.