Palaeoecological patterns of change in marine invertebrate faunas across the End-Triassic mass extinction event: Evidence from Larne, Northern Ireland

Abstract

The End-Triassic mass extinction event [ETE] (201.5 Ma) marks a drastic turnover and loss of >50% of marine biodiversity. Suggested environmental factors include extreme climate change and global carbon-cycle perturbations linked to Central Atlantic Magmatic Province (CAMP) volcanism. Considerable attention has been paid to disentangling the causes and selectivity of the ETE, whilst downplaying the patterns of change in the structure and functioning of marine paleofauna. Here we provide detailed quantitative information from across the Triassic-Jurassic boundary at Waterloo Bay, Larne, Northern Ireland, to describe patterns of changes in different palaeoecological parameters across the ETE. The analysis was based on abundance data of species sampled from approximately 1 m intervals through the sequence. Dominance and richness were estimated using rarefaction techniques and β-diversity index, and distinctness diversity indices were calculated. Changes in species composition were evaluated by multivariate analysis (nMDS, ANOMSIM and SIMPER). Rank abundance models were fitted, and functional diversity were estimated based on an ecospace model, applied to each sampled unit to detect changes in structure and ecological complexity. Across the ETE three distinctive states were identified: the pre-extinction state (Westbury Formation), characterised by an assemblage with high species richness and ecological redundancy, and with low taxonomic variation and functional diversity. The extinction state (Cotham and Langport members) represents a shift of the marine ecosystem, where >70% marine species disappears decreasing the ecosystems functioning the marine ecosystem around 80%. The recovery state (Lias Group), commencing some ~150 ky after the extinction, with ecologically complex assemblages as new taxa colonised, increasing variation in taxonomic distinctness and new contributing ecological traits and functional richness through the Hettangian. The palaeoecological patterns described here are robust enough to discount possible facies effects, but more important, is consistent with other studies reported globally, and demonstrates that the ecological signals detected in this study are real.