Changes in terrestrial floras at the Triassic-Jurassic Boundary in Europe
Maria Barbacka, Grzegorz Pacyna, , Ádam T. Kocsis, , Agata Jarzynka, Jadwiga Ziaja, , Emese Bodor
One of the biggest mass extinctions took place at the Triassic-Jurassic Boundary. It affected both marine and terrestrial ecosystems, and caused the disappearance of many animal taxa, mostly marine ones. Its influence on floral changes has been widely discussed, with arguments offered for the sudden mass extinction of plants over vast areas, or, alternatively, for slow, less extensive changes. The aim of this study was to statistically verify changes in terrestrial plant composition during the TJB in Europe, and to examine the type and extent of these changes. Data from Polish localities, an interesting new addition to the floristic data from the TJB, were compared with those from other selected localities in Europe. The database contains 311 macroflora taxa from 106 localities (16 Polish) in 13 countries, grouped into 29 regions; and 571 microflora taxa from 105 localities (29 Polish) in 11 countries, grouped into 37 regions. The analysed data cover the period from the Anisian to the Toarcian stages.
Range-based metrics for diversity dynamics were calculated to show trends in floral changes during the studied time interval, the focus being on the TJB. Due to strong disproportions in the number of localities and occurrences, the Rhaetian and the Hettangian stages were overrepresented. The warm and humid climate of those stages promoted plant diversity and led to the formation of numerous broad floodplains conducive to the preservation of remains (e.g. in coal). The patterns established by the raw data analyses were also assessed by applying a sampling standardisation procedure. Our results, based on accurate data from Poland and the rest of Europe, confirm and visualize a scenario in which there were no significant changes in terrestrial plant composition at the TJB. Hierarchical clustering suggests that local habitat conditions are the key factor in the grouping of localities with similar floristic composition, and that differences between floras are not associated with the time dimension (stages).
Keywords: Rhaetian; Hettangian; Floral change; Plant diversity
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