Exceptionally preserved soft-bodied assemblage in Ordovician carbonates of Anticosti Island, eastern Canada

Abstract

Abstract A diverse benthic fauna containing exceptionally preserved soft-bodied organisms is described from the new Vaureal Konservat-Lagerstatte from the Upper Ordovician Vaureal Formation (Katian) of Anticosti Island, Canada. These fossils occur as pyritic (or goethitic, if weathered), calcitic aggregates or sediment-filled voids on micritic bedding planes of a marlstone-limestone alternation originated on a shallow tropical carbonate ramp. Many organisms are preserved in association with their traces (e.g. burrows, trails), whose changing shapes indicate increasing cohesiveness of the substrate. Rapid burial (obrution) under dysoxic bottom conditions must have favoured exceptional preservation. Although anatomical details of the organisms are often lacking due to recrystallization, members of different groups of organisms could be interpreted based on their shape and other characteristic features, including those of which represent their oldest fossil record (i.e. Acoelomorpha, Turbellaria, Nemertea, Nematoda), beside Polychaeta, Sipuncula, Ostracoda and other Arthropoda. In parallel with molecular data, which recently have changed the phylogenetic status of some clades, this soft-bodied fauna and their traces not only record their appearance but add to the understanding of their body plan and behaviour. The new Konservat-Lagerstatte provides important information about a diverse benthic community in the Late Ordovician after the Great Ordovician Biodiversification Event (GOBE), and represents a calibration point for comparison across the Late Ordovician mass extinction. Moreover, comparable Fossil-Lagerstatten are probably more common in shallow-marine carbonates than currently known but might have been simply overlooked.