Global proliferation of opportunistic pleuromeian lycopsids following the disappearance of the end-Triassic forests

Abstract

Abstract Environmental crises and mass extinction events on land are typically followed by ecological upheaval, during which opportunistic plants rapidly colonize devastated landscapes, forming transient ‘pioneer’ communities that precede the establishment of complex forest ecosystems. Here, we identify such a pattern in the aftermath of the end-Triassic mass extinction event ~201 million years ago. We document the final global occurrence of the pleuromeian lycopsids within Lower Jurassic (Hettangian) strata of Sweden and demonstrate biological links between the parent plant Lycostrobus scottii and its mega- and micro-spores. By tracing occurrences of its distinctive megaspores, Nathorstisporites hopliticus , we reconstruct the temporal and geographic distribution of L. scottii across the Triassic–Jurassic boundary. We employed morphological characters to construct the first detailed phylogenies of Devonian to Jurassic lycopsids (including L. scottii ) using (1) Bayesian inference, (2) a parsimony approach with equal weighting, and (3) another with implied weighting. Phylogenetic analyses recovered Lycostrobus scottii as the youngest known representative of Pleuromeiaceae, which is positioned as sister to Chaloneriaceae. This topology suggests an early origin of Pleuromeiaceae, either nested within or sister to Chaloneriaceae, and implies that the evolutionary history of the group includes a long Carboniferous–Permian ghost lineage. Our findings indicate that pleuromeian lycopsids underwent a short-lived but widespread ‘bloom’ immediately following the collapse of Late Triassic forest ecosystems, forming opportunistic pioneer communities in the earliest Jurassic, before vanishing from the geological record soon thereafter.