Pdf: http://www.tdr.cesca.es/TESIS_UV/AVAILABLE/TDX-0420110-162007//ros.pdf

The main goal of this PhD dissertation is the study of the marine bivalve generic palaeodiversity throughout the Induan (Lower Triassic) – Sinemurian (Lower Jurassic) [In – Sin] interval, which includes two recovery processes, namely those of the Permo-Triassic (P/T) and Triassic – Jurassic (T/J) extinctions. A database was prepared from papers with graphic and/or descriptive information of taxa, excluding genera which were neither present nor valid throughout the interval. In addition, stratigraphic ranges (with comparison Treatise on Invertebrate Palaeontology and Compendium of Fossil Marine Animal Genera) and paleobiogeographic distributions as well as mode of life (guilds, mobile or attached, and position referred to the water column and substrate), and shell mineralogy have been re-examined. Taphonomic biases have been assessed by means of an analysis of contingency tables with adjusted residuals for different databases. In spite of having considered several biasing factors (mode of life, eurytopy or stenotopy, and so on) influencing preservation of bivalves throughout the [In – Sin], we have only recognised the strong influence of mineralogy associated to rarefaction, as it occurs during the Fanerozoic. Through the filtered data, estimates of origination, extinction and growth rates, and perform cohort analysis have been obtained. Differences in rates produce fluctuations of taxonomic diversity throughout [In – Sin]. Cohort analysis evidences detailed extinction patterns of genera arisen in each stage or the epifaunal in contrast with the infaunal genera. Finally, changes in the bivalve ecospace are studied during the [In – Sin] interval, with special emphasis on the impact of the T/J extinction. The main conclusions are 1) ecological tiering shows a very low development during the Lower Triassic as a consequence of the P/T extinction, but it is recovered during the Middle Triassic; after the T/J extinction, bivalve tiering has been scarcely affected. 2) infaunal genera became more and more abundant; this trend began since the Upper Triassic and went on the Lower Jurassic. 3) 42% of genera become extinct during the T/J extinction; impoverishment was due to a high extinction rate jointly to low origination rate; however, the diversity of guilds was not altered; this suggests that taxonomic extinction was decoupled from ecological dynamics.