Coping between crises: early triassic–early jurassic bivalve diversity dynamics

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Palaeogeography, Palaeoclimatology, Palaeoecology 311 (2011) 184–199

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Palaeogeography, Palaeoclimatology, Palaeoecology
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Coping between crises: Early Triassic–early Jurassic bivalve diversity dynamics
Sonia Ros a, b,⁎, Miquel De Renzi a, b, Susana E. Damborenea c, Ana Márquez-Aliaga a, ba b c

Departamento de Geología, Universidad de Valencia. Avda. Dr. Moliner, 50, 46100, Burjassot, Valencia, Spain Instituto Cavanilles de Biodiversidad y Biología Evolutiva, Universidad de Valencia. Apartado Oficial 22085, 46071, Burjassot, Valencia, Spain CONICET and Departamento de Paleontología de Invertebrados, Museo de Ciencias Naturales de La Plata, Paseo del Bosque s/n, 1900, La Plata,Argentina

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The Triassic is bounded by two of the most severe biotic crises, but nevertheless this time was, for bivalves, both a recovery and a diversification period, and a moment to fully exploit some of their evolutionary novelties. Just how and when this was achieved is analyzed in this paper, which covers Induan to Sinemurian bivalve diversity,based on a newly compiled database. Taxonomic diversity and ecospace dynamics are examined separately. Diversity and evolutionary rates were assessed, extinction selectivity was tested using a resampling algorithm, and cohort analysis was used to study extinction patterns. During the Early Triassic most bivalve genera were survivors from the Permian and they were mainly cosmopolitan epifaunal andsemi-infaunal endobyssate taxa. Reclined, epifaunal and semi-infaunal bivalves increased in diversity during the Triassic, but from Norian on, their diversity declined, and they were strongly affected by the T/J crisis. Although the Triassic/Jurassic extinction strongly impacted bivalve taxonomic diversity, it had little impact on bivalve ecologic diversity. Not a single bivalve life strategy waseliminated at the end of the Triassic. The present study does not support previous conclusions that infaunal bivalves suffered greater extinction than epifaunal ones during the T/J extinction. Not all life strategies were equally affected by the extinction event, being the deep infaunal burrowers positively selected. Bivalves with major energetic requirements seem to have been more affected withnegative selectivity on fast shallow burrowers. The ecologic diversity changes of bivalves during the Late Triassic and several adaptations of durophagous predators reflect the effects of increasing predation pressure and support a Late Triassic origin of the Mesozoic Marine Revolution. © 2011 Elsevier B.V. All rights reserved.

Article history: Received 24 April 2011 Received in revised form18 August 2011 Accepted 27 August 2011 Available online 3 September 2011 Keywords: Bivalvia Triassic Permian/Triassic extinction Triassic/Jurassic extinction Biotic recovery Extinction selectivity

1. Introduction Bivalves are a highly diversified molluscan class, with a long history dating from Early Cambrian times (Cope, 2000). Although the group already showed a steady diversification trendduring the Paleozoic, it only became highly successful and expanded rapidly from the Mesozoic onwards. The Triassic was, for bivalves, first a recovery period and later a biotic diversification time. It was also the time when bivalves first fully exploited some of their evolutionary novelties. The Triassic was bounded by two severe biotic crises: the P/T and T/J, both of which are included in the “bigfive” extinction events, which had devastating effects on a global scale (Newell, 1967; Raup and Sepkoski, 1982). The P/T extinction event was the most severe biotic crisis in the history of life on Earth (Raup, 1979; Raup and Sepkoski, 1982; Erwin, 1993, 2006), not only in terms of taxonomic losses but also in terms of the drastic re-organization of marine ecosystems (Erwin, 2006; Wagner

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