SMALL TAXONOMIC AND LARGE ECOLOGICAL EFFECTS OF THE END-GUADALUPIAN EXTINCTION (LATE PERMIAN)

The mass extinction during the Permian-Triassic transition has long been recognized as the most severe biotic crisis of the Phanerozoic, eliminating close to 95% of marine species and fundamentally altering the ecological structure of marine ecosystems by decimating the Paleozoic Fauna and giving rise to the Modern Fauna. However, it has only been realized during the last decade that the Late Permian biotic crisis was composed of two independent events: the end-Guadalupian extinction at the Middle-Late Permian boundary (260 Ma) and the end-Permian extinction (252 Ma). Taxonomic measures of the earlier end-Guadalupian event suggested that the genus-level extinction rate was 60%, implying that the extinction was surpassed in magnitude only by the later end-Permian crisis, and also showed that the extinction was strongly selective, preferentially affecting members of the Paleozoic Fauna. In contrast to this taxonomic work, no studies have separated the ecological effects of the end-Guadalupian and end-Permian extinctions, and the role the end-Guadalupian crisis played in the ecological transition between the Paleozoic and Modern Faunas remains unknown. We compiled a new global database of Middle Permian to Early Triassic diversity patterns in order to reassess the taxonomic pattern of the end-Guadalupian extinction and documented the relative abundance of macrofossils in Middle and Late Permian fossil assemblages to quantify end-Guadalupian changes in ecological dominance. The new taxonomic compilation shows that the end-Guadalupian extinction had a genus-level extinction rate of only 38%, much smaller than previously thought, but confirms that it was strongly selective, as the brachiopod extinction rate of 42% was more than double the 18% among bivalves. Despite this moderate taxonomic severity, the end-Guadalupian extinction had an extremely profound ecological impact. The relative within-assemblage abundance of bivalves and gastropods increased immensely, from an average of 1.5% in the Guadalupian to nearly 50% in the Lopingian. These results indicate that the end-Guadalupian extinction was responsible for a much larger part of the ecological switch in relative abundance between the Paleozoic and Modern faunas than previously thought, despite its moderate taxonomic effects.