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Resumen:
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The external and internal features, microstructure, and distributions of Coniacian rhynchonellides from the Northern Castilian Platform (Northern Spain) have been studied here. In addition, the revision of numerous European Upper Cretaceous brachiopod collections (e.g., d’Orbigny, 1842-1851; Coquand, 1860, 1862, 1879; Owen, 1962, 1988) has contributed to systematic, biostratigraphic, and palaeobiogeographic precisions. The genus Woodwardirhynchia has been identified for the first time in Spain, represented by W. pontemdiaboli sp. nov., whose range is restricted to the basal Coniacian (Forresteria petrocoriensis zone). This species is characterized by slightly dorsibiconvex shells and antidichotomous ornament with medially rather and anteriorly concave crura. The genus Cyclothyris, well characterized by its long dorsally concave crura, is also recognized. This group is represented in the lower Coniacian (Tissotioides haplophyllus zone) by C. segurai sp. nov., and in the middle and basal upper Coniacian (Gauthiericeras margae zone and lower part of the Hemitissotia turzoi zone) by C. cardiatelia sp. nov. Cyclothyris segurai is an equibiconvex rhynchonellide with a low fold ornamented with rounded ribs, while C. cardiatelia is an asymmetric species with two well-differentiated lobes in the shell, the ventral beak being twisted towards the larger lobe. The study and revision of these three species has also allowed the systematic reassignment of specimens previously classified as Rhynchonella petrocoriensis, Rhynchonella difformis var. globata, Cyclothyris claudicans, Owenirhynchia claudicans, and Cyclothyris aff. globata. The revision of the palaeobiogeographical data concerning the studied assemblages has led to the proposition of two new biochoremas, the Anglo-Paris Subprovince and the Biscay Subprovince.
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