Integrated Regional Diversity Analysis of the Early Triassic Ammonoid Recovery

Following the end-Permian mass extinction ammonoids experienced an explosive recovery, with taxonomic diversity levels as high as pre-crisis ones reached in less than 2 my after the P/T boundary [1-4]. In order to assess the patterns, rhythms and modalities of this radiation, we perform an integrated diversity analysis based on generic incidence data tables (with revised taxonomy)constructed at the regional, i.e. basin level for each of the four Early Triassic substages (Griesbachian, Dienerian, Smithian and Spathian). The cross-characterization of regional taxonomic assemblages distributed worldwide from taxonomic and phenetic diversities, taxonomic distinctness and geographic rarity points of view, coupled with the structure and evolution of geographic concordance between the analyzed taxa, enable us to characterize the biotic and abiotic control parameters driving the post-P/T crisis ammonoid radiation. In association with Geophyletic Model simulations [5-7] and compositional similarity analysis [8-9], our results highlight the major explanatory power of the latitudinal gradient of temperature for the shaping of the Early Triassic ammonoid recovery.

[1] Brayard, A. et al. 2006: PPP 239.

[2] Brayard, A. & Bucher H. 2008: Fossils & Strata 55.

[3] Galfetti, T. et al. 2007: EPSL 258.

[4] Brühwiler, T. et al. in press: Palaeontology.

[5] Brayard, A. et al. 2004: Pal Elec 7.

[6] Brayard, A. et al. 2005: JZSER 43.

[7] Escarguel, G. et al. 2008: JZSER 46.

[8] Brayard, A. et al. 2007: Geobios 40.

[9] Brayard, A. et al. in press: JAES.