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The body size of marine ectotherms is often negatively correlated with ambient water temperature, as seen in many clades during the hyperthermal crisis of the end‐Permian mass extinction (c. 252 Ma). However, in the case of ostracods, size changes during ancient hyperthermal events are rarely quantified. In this study, we evaluate the body size changes of ostracods in the Aras Valley section (northwest Iran) in response to the drastic warming during the end‐Permian mass extinction at three taxonomic levels: class, order, species. At the assemblage level, the warming triggers a complete species turnover in the Aras Valley section, with larger, newly emerging species dominating the immediate post‐extinction assemblage for a short time. Individual ostracod species and instars do not show dwarfing or a change in body size as an adaptation to the temperature stress during the end‐Permian crisis. This may indicate that the ostracods in the Aras Valley section might have been exceptions to the temperature–size rule (TSR), using an adaptation mechanism that does not involve a decrease in body size. This adaptation might be similar to the accelerated development despite constant instar body sizes that can be observed in some recent experimental studies of ostracod responses to thermal stress. [ABSTRACT FROM AUTHOR]

The biggest known mass extinction in the history of animal life occurred at the Permian–Triassic boundary and has often been linked to global warming. Previous studies have suggested that a geologically rapid (<40 kyr) temperature increase of more than 10°C occurred simultaneously with the main extinction pulse. This hypothesis is challenged by geochemical and palaeontological data indicating profound environmental perturbations and a temperature rise prior to the main extinction. Using secondary ion mass spectrometry (SIMS), we measured oxygen isotope ratios from Changhsingian (late Permian) ostracods of north‐western Iran. Our data show that ambient seawater temperature began to rise at least 300 kyr prior to the main extinction event. Gradual warming by approximately 12°C was probably responsible for initial environmental degradation that eventually culminated in the global end‐Permian mass extinction. [ABSTRACT FROM AUTHOR]

The Aras Valley section (north‐west Iran) exposes a sedimentary succession that allows the study of ostracod diversity patterns during/across the end‐Permian mass extinction. For the present study, 59 samples were investigated for their ostracod abundances, which ranged from 4 to 31 500 specimens per 500 g. In 45 sample horizons, the ostracods were identified to the species level. In total, 3 425 specimens were determined and 62 species were identified, of which one genus and ten species are described for the first time: Fabalicypris veronicae Gliwa, sp. nov., Orthobairdia capuliformis Gliwa, sp. nov., Araxobairdia formosa Gliwa, gen. et sp. nov., Bairdiacypris kathleenae Gliwa, sp. nov., Eumiraculum mettei Gliwa, sp. nov., Liuzhinia julfensis Gliwa, sp. nov., Carinaknightina hofmanni Gliwa, sp. nov., Cavellina fosteri Gliwa, sp. nov., Cavellina hairapetiani Gliwa, sp. nov. and Hungaroleberis striatus Forel, sp. nov. The assemblages show, at the end‐Permian mass extinction event, a complete turnover from a low‐diversity Fabalicypris‐dominated pre‐extinction community to a more diverse Bairdiacypris‐dominated post‐extinction community. The turnover coincides with the significant temperature increase that was previously recorded from north‐west Iranian sections. The low diversity in the horizon immediately below the extinction horizon indicates that environmental changes, such as thermal stress, may have had an impact on the ostracod assemblages prior to the extinction event. In comparison with other diverse ostracod assemblages from the Palaeotethyan realm, the ostracods of the Aras Valley section are not associated with microbialites. [ABSTRACT FROM AUTHOR]

The Permian–Triassic boundary section in the Aras Valley in NW Iran is investigated with respect to carbonate microfacies, biostratigraphy (particularly conodonts, nautiloids, and ammonoids), chemostratigraphy (carbon isotopes), and environmental setting. Correlation of the data allows the establishment of a high-resolution stratigraphy based on conodonts (with four Wuchiapingian, 10 Changhsingian, and three Griesbachian zones), ammonoids (with nine Changhsingian zones), and carbon isotopes; it forms the base for the reconstruction of the environmental changes before and after the end-Permian extinction event at the studied locality. In the Aras Valley section, there is no evidence for the development of anoxic conditions, associated with the end-Permian mass extinction. [ABSTRACT FROM AUTHOR]