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Dryad

Bivalve body size distribution through the Late Triassic mass extinction event

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Nov 10, 2021 version files 309.54 KB

Abstract

The synergic relationship between physiology, ecology and evolutionary process makes the body size distribution (BSD) an essential component of the community ecology. Body size is highly susceptible to environmental change, and extreme upheavals, such as during a mass extinction event, could exert drastic changes on a taxon’s BSD. It has been hypothesized that the Late Triassic mass extinction event (LTE) was triggered by intense global warming, linked to massive volcanic activity associated with the Central Atlantic Magmatic Province. We test the effects of the LTE on the BSD of fossil bivalve assemblages from three study sites spanning the Triassic/Jurassic boundary in the UK. Our results show that the effects of the LTE were rapid and synchronous across sites, and the BSDs of the bivalves record drastic changes associated with species turnover. No phylogenetic signal of size selectivity was recorded, although semi-infaunal species were apparently most susceptible to change. Each size class had the same likelihood of extinction during the LTE, which resulted in a platykurtic BSD with negative skew.  The immediate post-extinction assemblage exhibits a leptokurtic BSD although with negatively skewed, where surviving species and newly appearing small-sized colonizers exhibit body sizes near the modal size. Recovery was relatively rapid (~100kyr), and larger bivalves began to appear during the Pre-Planorbis Zone, despite recurrent dysoxic/anoxic conditions. This study demonstrates how a mass extinction acts across the size spectrum in bivalves and shows how BSDs emerge from evolutionary and ecological processes.