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A high-diversity Hirnantia fauna during the late Ordovician mass extinction event, Anticosti Island, Québec, eastern Canada

Jin, Jisuo1; Copper, Paul2

Published Oct 01, 2026 on Dryad. https://doi.org/10.5061/dryad.ngf1vhj9m

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Abstract

A high-diversity, high-richness Hirnantia fauna from the Late Ordovician (Hirnantian) strata of the Ellis Bay and basal Becscie formations comprises 58 species of brachiopods, among which 26 are either described for the first time from this stratigraphic interval of Anticosti Island or taxonomically updated. The early Hirnantian part of the fauna consists of both holdover genera (e.g., Hebertella, Plaesiomys, Vellamo) from the late Katian and first appearance of typical Hirnanian forms, such as Cliftonia, Eospirigerina, Eostropheodonta, Hindella, Hirnantia, Mendacella). The late Hirnantian components are characterized by either reef-dwelling, relatively large shells of Hirnantia and Hindella, or more commonly by dwarfed species of Dalmanella, Eospirigerina, Gnamptorhynchos, Hindella, Koigia, Mendacella, and Platytrochalos. New taxa include Eospirigerina loutra n. sp., Eospirigerina advena n. sp., Hindella natiscoteca n. sp., Koigia alpha n. sp., and Eohyattidina boltoni n. gen. n. sp. Eight brachiopod associations were recognized using quantitative analysis of α-diversity and multivariate (cluster and principal component) analyses of 26 sufficiently large Hirnantian brachiopod samples. There was a broad trend of higher α-diversity for samples and associations in relatively deep-water (mid-shelf) settings of western Anticosti as well as in reefal-biostromal facies of eastern Anticosti, but lower diversity in shallow-water (inner-shelf), level-bottom brachiopod associations in eastern Anticosti. Cluster analysis of global Hirnantia faunas indicates that the Anticosti Hirnantia fauna had a close affinity to the paleotropical, warm-water Edgewood-Cathay faunal province during the Hirnantian.