Taxonomy, biodiversity, paleoecology, and paleobiogeography of Wenlock brachiopod fauna from Arctic Canada.

摘要

In this thesis, the evolution of the Silurian brachiopod fauna in Arctic Canada was treated at two major scales: 1) the evolution of Epitomyonia and Dicoelosia was studied at the generic and specific scale to assess the range of morphological variation and ecological adaptation of a single genus in time and space, and 2) the evolution of the entire brachiopod fauna was examined to reveal broad trends of its diversity changes, global faunal provincialism, and paleoenvironmental implications.;The Homerian brachiopod radiation event comprised two episodes in Arctic Canada. The first episode occurred in the dubius-nassa Biozone, characterized by a high origination rate of brachiopod genera. The second episode took place in the ludensis Biozone, marked by the highest taxonomic diversity and a high extinction rate thereafter. The brachiopod groups contributing to the radiation event included orthides, pentamerides, atrypides, and spiriferides. Multivariate analyses of brachiopod collections recognized seven brachiopod assemblages, including Salopina, Spondylopyxis and Conchidium assemblages, dominated by brachiopod taxa of relatively shallow-water origin, and the Epitomyonia, Dicoelosia, Isorthis, and Jonesea assemblages, dominated by deeper water brachiopod genera. The brachiopod genera in each assemblage were reconstructed to their original living position with reference to their paleoecological ranges known from in-situ preservation in other regions. The multivariate analyses of global Wenlock brachiopod faunas corroborated the faunal difference between the Uralian-Cordilleran and North Atlantic biogeographical regions. The faunas from Arctic Canada have higher affinity indices with the faunas from the Uralian-Cordilleran Region than with the faunas from North Atlantic Region, indicating the persistence of the Uralian-Cordilleran paleobiogeographical region and its close link to the northern margin of Laurentia.;KEYWORDS: Epitomyonia, Dicoelosia, brachiopod fauna, Evolution, biodiversity, paleoecology, paleobiogeography, Wenlock, Arctic Canada;Studies of the global Epitomyonia-bearing faunas revealed that Epitomyonia lived in a relatively shallow-water environment in Late Ordovician but shifted largely to deep water by early Wenlock time. The Dicoelosia species, however, originated from outer shelf environment and expanded into shallower- and deeper-water depositional settings during the Late Ordovician. The Silurian and Devonian Dicoelosia species followed a similar evolutionary pattern as their Ordovician counterparts but were confined to shallow water in the Early Devonian.