Vegetation responses during the end-Triassic biotic crisis: Mass rarity, mutations and extinctions

Greenhouse gas emissions from large-scale volcanism in the Central Atlantic Magmatic Province (CAMP) are considered to have caused the end-Triassic mass extinction (ETME; 201.5 million years ago), but the impact on land plants has been debated, with some researchers suggesting that there was no extinction in plants during this biotic crisis. Yet, multiple spore-pollen records across the Triassic–Jurassic boundary testify that many plants were severely decimated at the end of the Rhaetian (the latest Triassic) with some going extinct already during the crisis and some lingering on into the earliest Jurassic before ultimately disappearing from the fossil record. For plants, the concept of mass rarity—i.e., the reduction in abundances and/or reduction in geographic ranges of several species contemporaneously—may be more important than taxonomic extinction when evaluating the severity of a biotic crisis. In Triassic–Jurassic boundary successions from the European epicontinental sea and the northern European Tethys margin, two distinct phases of mass rarity in spores and pollen are recorded. During these two mass rarity phases, both previously dominant and rare plants were affected, which testifies to the devastating consequences the environmental and climatic effects of the CAMP-volcanism had on the terrestrial ecosystem. Combined stress from rising air temperatures, changing climate, wildfires, and volcanicinduced heavy metal pollution, was exacerbated by fragmentation and destruction of coastal and near-coastal lowland mire habitats during rapid sea-level changes most likely linked to crustal deformation due to on-going magma emplacement. The responses of the vegetation are recorded as mass rarity, mutations, lingering of ghost taxa, restructuring of ecosystems and extinctions. This should resonate with ongoing and future climate change as it attests to the vulnerability of coastal and lowland vegetation to climatic and environmental disturbances, including rapid sea-level changes, which threatens entire ecosystems.