Late Silurian brachiopods Dayia and Shaleria as indicators of environmental changes during the ’Lau/Kozlowskii Bioevent’ on both sides of the Rheic Ocean

Paleogeographic differences in temperature, water depth and conodont biofacies during the Late Devonian

The Carboniferous is characterized by drastic climatic and environmental fluctuations, which include multiple phases of glaciation resulting in an icehouse climate. Additionally, dynamic continental reconfigurations forced the contraction of the Rheic Ocean resulting in the closure of the Rheic–Tethyan Gateway, which precluded further faunal exchanges between the North American and Eurasian marine realms. Interestingly, cartilaginous fishes seem to be relatively immune to these drastic climatic and environmental changes. The Eurasian fossil record of Paleozoic sharks is strongly biased towards intensively sampled localities from England, Ireland, Scotland, and the Russian Platform. Here we present rare dental material from the Serpukhovian (early Carboniferous) of Austria, adding new information to the paleogeographic distribution of ctenacanthiform sharks. The new material revealed the first record of the genus Saivodus in Central Europe and allowed us to recognize a new species, Cladodus gailensis sp. nov., and a remnant of fossilized cartilage. In an attempt to identify possible linkages between climatic or environmental fluctuations on shark diversity throughout the Carboniferous, we provide a synopsis of the distribution and diversity of elasmobranchs based on primary literature. This preliminary assessment at genus level indicates two pronounced events of extinction, with the first one occurring during the latest Mississippian and the second one towards the end of the Pennsylvanian. The first extinction event distinctly correlates with the known diversity decline of other marine inhabitants and the second occurred during an unstable period of multiple phases of glaciation.

Articulate brachiopods of the Llandovery rocks of the Severn River, Ekwan River and Attawapiskat formations of the Hudson Bay Lowlands comprise 35 genera and 50 species, including 18 new species: Severella pinnigera, Gypidula rudiplicativa, Rhytidorhachis guttuliformis, Rostricellula subtilicostata, Microsphaeridiorhynchus hercostomaticum, Hercotrema spissicostatum, Meifodia discoidalis, Atyrypoidea praelingulata, Atrypopsis severnensis, Parmula hemisphaerica, Merista rhombiformis, Whitfieldella pygmaea, Whitfieldella sulcatina, Howellella porcata, Alaskospira fabiformis, Dalejina striata, Eoplectodonta (Eoplectodonta) hudsonensis, and Protochonetes harricanensis. The species of Alaskospira, Atrypoidea and Merista represent unusually early appearances of these genera. The biohermal complexes of the Attawapiskat Formation provided a great diversity of environments. Some species with small shells seem to have occupied specialized and protected niches within the complexes, whereas large, thick shelled species occupied open water environments. Three brachiopod assemblage zones can be recognized. The Virgiana decussata Zone (dominantly pentamerids) is succeeded by the Hercotrema winiskensis�Stegerhynchus borealis Zone (dominantly rhynchonellids). Above, the Pentameroides septentrionalis�Lissatrypa variabilis Zone has a very varied fauna with abundant pentamerids and spire-bearers. Species diversity increases from 6, to 15, and to 36 species in the three zones. The changes in diversity and in taxonomic composition were probably related to the changes in environments during the Early Silurian transgression from dominantly intertidal and lagoonal to dominantly subtidal and reefal. Correlations with successions on Anticosti and Manitoulin islands indicate that the Severn River Formation is latest Rhuddanian to late Aeronian in age, the Ekwan River Formation is Telychian, and the Attawpiskat Formation is late Telychian. Comparison with the outcrop succession of southern Manitoba indicates correlation of the basal Severn River Formation with the Fisher Branch Formation; the remainder of the Severn River Formation with the Moose Lake or ``Inwood'' (sensu McCabe), Atikameg, and East Arm formations; and the Ekwan River and the Attawapiskat Formation with the Cedar Lake Formation, but with the uppermost Attawapiskat being slightly younger.