Devonian ostracods from western Canada — palaeozoogeographic implications

Abstract

The stratigraphical significance, evolutionary pathways and distribution patterns of Devonian (with emphasis on Middle Devonian) ostracods occurring in western Canada are reviewed. The overall faunal appearance is Devonian in aspect. Typical Eifelian-Givetian markers are ascertainable at the generic level, and occasionally resemble known species. Recognised genera mostly comprise cosmopolitan forms indicating (close or loose) faunal connections to both north and south, but also representing either Old World or true New World forms. A “core group”, however, shows a particular bauplan giving a unique aspect, mainly discrete palaeocopine genera, provided with particular extradomiciliar dimorphic features and considered to be endemic for the Middle Devonian of western Canada. In terms of palaeozoogeography, faunal relationships inside Canada and to Devonian occurrences overseas are demonstrated. Connections between sedimentary transgressive-regressive and evolutionary cycles are demonstrated in terms of event-stratigraphy. Against the background of plate tectonic analyses, assumed migration paths are considered, probably northward via the Uralian Sea to Siberia, but certainly and on a larger scale southward across the Rheic Ocean to North Africa (southwestern Morocco, central Sahara) and Europe (Eifel region, eastern Thuringia, Holy Cross Mountains). As a result, the faunal relationship to the adjacent Great Lakes region appears to be much closer than originally predicted, while only loose contacts are traceable to the North American Midcontinent region. The North African and central European relationships are revealed by few, but conspicuous genera and, to some extent, this may be true of the Russian Platform and Bashkiria.