SIGNALS FROM THE SHALLOWS: THE RECORD OF LATE ORDOVICIAN-LATE SILURIAN ARTHROPOD DIVERSITY IN MARGINAL MARINE KONSERVAT-LAGERSTÄTTEN OF CENTRAL CANADA

Cambrian Konservat-Lagerstätten, including both Burgess Shale- and Orsten-type deposits, continue to yield a wealth of data on the early and rapid diversification of Arthropoda, especially those groups lacking pervasively biomineralized cuticles. This window of exceptional preservation reopens for the Late Paleozoic (Devonian - Carboniferous) record, arguably at fewer sites but on an expanded ecological scale as arthropods moved from aquatic environments to permanently occupy the terrestrial realm. Until recently, equivalent Ordovician and Silurian Lagerstätten deposits were not well known, and the intervening record of non-biomineralizing arthropod clades was much more tenuous by comparison.

Evidence emerging from new sites, together with that gleaned through reappraisal of earlier discoveries, is now beginning to expand our knowledge of post-Cambrian – pre-Devonian non-trilobite arthropods across a critical gap encompassing the Great Ordovician Biodiversification Event, end-Ordovician extinctions, and Silurian biotic recovery. In this temporal context, four Konservat-Lagerstätten deposits in central Canada are proving important for developing a picture of arthropod (in particular, chelicerate) evolution and diversity in shallow subtidal and lagoonal settings on the Laurentian paleocontinent. In Manitoba, the William Lake and Airport Cove biotas (Late Ordovician, Late Katian) include well-preserved eurypterids and xiphosurids; stem-group pycnogonids, along with a few enigmatic arthropods, are also known from the former. The Silurian record is represented in Ontario by the Eramosa (Sheinwoodian) and the Bertie (Pridolian) Lagerstätten, which have between them produced a diverse suite of eurypterids, ‘synziphosurans’, scorpions, and phyllocarid crustaceans. The Eramosa biota, in addition, includes lobopodians and a number of non-biomineralized euarthropods of uncertain affinities.

Initial investigations (or, in the case of the Bertie, reassessment) of arthropod fossils from these sites have already revealed novel phylogenetic and paleoecologic insights. Acquisition of larger sample sizes and the application of new methodologies and technologies hold further promise for extracting even stronger signals from a formerly obscure interval of arthropod evolution.