Bounded by crises: An overview of the evolution of marine ostracods during the Triassic
Résumé
The Triassic has been a turning in the history of biodiversity: bracketed by two major biotic crises, characterized by major biotic, climatic and tectonic events, it has seen the transition from the Palaeozoic to the Modern evolutionary faunas. We propose the first synthetic analysis of the diversity of marine and brackish-water ostracods over the entire Triassic, in the light of palaeoecological, palaeoenvironmental and palaeogeographical contexts. Although general diversity trends witness poor ostracod communities during most of the Early Triassic after the end-Permian crisis, the roots of their Triassic taxonomic rediversification are visible as early as the Dienerian. The explosive diversification of the Spathian and Anisian is followed by a high-diversity plateau up to the brink of the end-Triassic extinction. A "morphological phylogeny" proposes that all Permian and Triassic ornate Bairdiidae derived from Petasobairdia in the Kungurian, with the emergence of the Ceratobairdia-lineage and Abrobairdia-lineage. While they are generally the "poor cousin" of trophic chains analyses, traces of typical Mesozoic drilling predation on Late Triassic ostracods unexpectedly document the increase of the efficiency of predators drilling abilities through the Triassic. Finally, the palaeogeographical distribution of ostracods as been very dynamic during this interval, with distinct peri-palaeo-tethyan and peri-neo-tethyan biotas in the Early Triassic, followed by a dispersal and thus a relative homogenization from the Anisian onwards.
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