Article: Early evolution of Declinognathodus close to the Mid-Carboniferous Boundary interval in the Barcaliente type section (Spain)

Upper Serpukhovian to lower Bashkirian conodonts studied from the lower and middle part of the Barcaliente Formation type section (NW Spain) are not abundant, but the sedimentary record seems unusually well represented. The first occurrence of Declinognathodus bernesgae occurs more than 140 m below the first occurrence of D. inaequalis, the taxon of the D. noduliferus species group appearing in the bed of the Global Standard Stratotype-section and Point (GSSP) for the Mid-Carboniferous Boundary (Arrow Canyon, Nevada). P1 elements transitional between D. bernesgae and D. inaequalis are described and considered relevant to the global correlation of the Mid-Carboniferous Boundary. In addition, D. praenoduliferus, D. cf. noduliferus, D. lateralis, Idiognathoides asiaticus, I. corrugatus and Neognathodus sp. are described and illustrated from the Barcaliente Formation. A phylogeny is proposed for the early species of these genera on the basis of the morphological changes of the P1 element, where the rostral parapet and area, the surface roughness and the length and depth of the adcarinal troughs are diagnostic characters at the specific level, while caudal ornamentation is a secondary taxonomic character.