A new species ofHirnantia(Orthida, Brachiopoda) and its implications for the Hirnantian age of the Ellis Bay Formation, Anticosti Island, eastern Canada

Abstract

AbstractAnticosti Island, eastern Canada, records an exceptionally thick and well-exposed Ordovician/Silurian boundary section that hosts a series of diverse marine invertebrate faunas across the Late Ordovician mass extinction. However, the base of the terminal Ordovician stage, the Hirnantian, has been difficult to identify on Anticosti due to the lack of a traditionalHirnantiafauna within the Upper Ordovician Ellis Bay Formation. Previously, the eponymous taxon of theHirnantiafauna, and type species of the genusHirnantia,H. sagittifera(M'Coy, 1851) has been reported only from the uppermost Ellis Bay Formation, leading to uncertainty as to the age of the lower Ellis Bay Formation. Here we reportHirnantia notiskuanin. sp. from the lowermost Ellis Bay Formation. This new species is similar to the type species,H. sagittifera, but is distinguished by its strongly dorsibiconvex shell in mature forms and variously developed uniplicate anterior commissure. Occurrences of these two similar species ofHirnantia,H. notiskuaniandH. sagittifera, within the lower and uppermost Ellis Bay Formation, respectively, indicate a Hirnantian age for the entire Ellis Bay Formation, a finding that is supported by recent palynological and chemostratigraphic studies. Brachiopod assemblages within the Ellis Bay Formation therefore are best characterized as a unique and diverseHirnantiafauna, consisting of genera from both the typicalHirnantiafauna and the epeiric seas of Laurentia.UUID:http://zoobank.org/1c1dff6a-ee38-4cd3-b8bd-3d803a2774ef