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Brachiopods from volcanoclastic Middle and Upper Ordovician of Asturias (northern Spain)
Published online by Cambridge University Press: 19 May 2016
Abstract
In the El Castro Formation, cropping out on the Asturian coast of northern Spain, two fossiliferous horizons have been studied. Above the basal one, containing the Llandeilian brachiopods Tissintia cf. T. convergens and Howellites? sp., a new horizon of estimated Ashgillian age has been identified that has yielded the new brachiopod species Mcewanella vulcanica and Hesperinia asturica. The new species of Mcewanella, close to the Irish Rawtheyan Mcewanella dorsisulcata, is characterized by a great delay of the insertion of costellae, which gives many adults a strikingly costate ornament for this genus. Hesperinia was, up to now, poorly known from a small number of specimens from the Llanvirnian Tank Hill Formation in Nevada; thus, the new record, besides allowing a better understanding of the genus and its relationship with other oepikinids, extends its known time span to the Late Ordovician. These two species were dwellers on a low-energy bottom formed of loose sand and gravel supplied by nearby volcanic eruptions. The ash-flow depositional pattern of these sediments would have had lethal effects on the brachiopod communities, periodically causing their destruction. These species of the genera Mcewanella and Hesperinia are new representatives of the immigration of North American and Northern European warm-water faunas into the circumpolar Mediterranean Province during the Late Ordovician.
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