New insights on Early Jurassic bivalves, pleurotomariid gastropods, and the Permian–Triassic mass extinction (PTME)

Specimen-based palaeobiological research combined with cutting-edge methods and models helps better answering questions about evolution and biodiversity throughout Earth’s history. New research on Lower Jurassic bivalves from Germany have revealed the oldest members of two bivalve families, the earliest evidence of sexual dimorphism in bivalves, and specialized drilling predatory behaviour by an extinct gastropod. Pleurotomariid gastropods, the extant clade with the longest fossil record and the most diverse Paleozoic gastropod group, which declined in diversity since the mid-Paleozoic, contrasting with the continued diversification of Gastropoda. New collections from the Carboniferous suggest pleurotomariids were not only diverse but also the most abundant gastropod clade in the Late Paleozoic. Taxonomic re-examination of type material and undescribed specimens in museums shows that nearly all Triassic pleurotomariid genera evolved after the Permian–Triassic mass extinction (PTME). Their slow recovery in the Triassic was disrupted by the Carnian Pluvial Episode, and they never regained Paleozoic diversity levels. A phylogeny of pleurotomariids (Ordovician–Recent), reconstructed using the Fossilized Birth-Death model, revealed no significant differences in evolutionary rates among branches or over time, suggesting that extinction and diversity decline were not driven by evolvability. The analysis also indicates that early ontogenetic shell characters are more conservative, challenging previous assumptions about phylogenetic value of shell characters. The PTME affected not only Pleurotomariida but the entire marine ecosystems, as evidenced by new fossil collections from Türkiye. The modelled trophic interactions across seven localities show that food webs did not collapse but restructured and became top-heavy (predator-dominated), especially in higher latitudes.