From Crisis to Recovery: Floral Turnover and Environmental Shifts During the Triassic–jurassic in Iran

The Iranian Plateau, situated along the southern margin of Laurasia, represents a key yet underexplored archive for understanding terrestrial vegetation dynamics across the Triassic–Jurassic transition. This study provides the first comprehensive statistical analysis of megafloral records from Iran spanning the Late Triassic (Norian) to the early Middle Jurassic (Bajocian). Patterns of taxonomic composition, diversity, and stratigraphic distribution reveal pronounced floral turnover across this interval. A marked decline in diversity occurs at the Triassic–Jurassic boundary, followed by recovery during the Sinemurian–Pliensbachian and renewed diversification in the Early Bajocian. Ferns remain the most persistent and diverse component throughout, while cycads show a shift from Bennettitales-dominated assemblages in the Late Triassic to increased prominence of Nilssoniales in the Jurassic. Concurrently, conifers and ginkgophytes expand as several seed fern groups decline. Five distinct floral zones are identified, reflecting changes in vegetation linked to depositional environments and tectonic activity associated with phases of the Cimmerian orogeny. Despite the reduction in diversity at the boundary, the results do not indicate a true extinction event; instead, floral turnover is best explained by regional palaeoenvironmental reorganization. These findings highlight the dominant role of regional environmental and tectonic processes in shaping vegetation dynamics on the Iranian Plateau during the Mesozoic.