The fossil wonders of the Silurian Eramosa Lagerstätte of Canada : the jawed polychaete faunas

University essay from Lunds universitet/Geologiska institutionen

Abstract: The Silurian Eramosa Lagerstätte in Ontario, Canada, is represented by three distinguished biotas (1 to 3) with exceptionally well preserved fossils. In this study, the jawed polychaete fauna is described and discussed for the first time, on the basis of scolecodonts and jaw apparatuses, recovered from Biota 1 and 3. One new paulinitid species, Kettnerites sp. a, is described from a wealthy collection of specimens recovered through acid digestion of rocks from the locality Park Head (comprising Biota 1), the strata of which were probably formed in very shallow, possibly lagoonal environments. The abundant and monospecific material allowed confident reconstruction of the full dorsal maxillary apparatus and the new taxon is compared to previously known, approximately coeval ones from other regions. Attempts at finding evidence of jaw moulting for Kettnerites sp. a were inconclusive; similar to a previous study from the Silurian of Gotland, Sweden, no unambiguous evidence for distinct size frequency classes was revealed. In addition to the Park Head collection, bedding plane material from the locality Wiarton (comprising Biota 3) revealed two other taxa; Kettnerites sp. b and Oenonites cf. curvidens. The strata at Wiarton have been interpreted as representing environments with good water circulation and open marine conditions. Based on their relative abundance, jaw bearing polychaetes apparently played a significant role in the Silurian marine biotas that are currently preserved in the Eramosa Lagerstätte and this study provides a fuller picture of this lagerstätte. Moreover, the results reinforce the fact that different polychaete species had variable environmental preferences during the Silurian and that Oenonites and Kettnerites formed two of the most common and widely distributed genera.

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