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

Abstract

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.

Facies, geometry and growth phases of the Valdorria carbonate platform (Pennsylvanian, northern Spain)

“…Phase I developed overlying the Barcaliente Formation and is dated as Serpukhovian–Early Bashkirian (Kinderscoutian; Sanz‐López & Blanco‐Ferrera, ) to late–Early Bashkirian (Akavasian Substage; Fig. A).…”

“…The growth of Phase I started at the end of the late Kinderscoutian-early Akavasian (around 320Á6 Ma) according to fusulinids (this study) and to the age established for the Porma Breccia (top of Barcaliente Formation according to Reuther, 1977) by Sanz-L opez & Blanco-Ferrera (2013). Fusulinids of the easternmost area provide an Askynbashian age, ending at ca 318Á2 Ma.…”

Conodont chronostratigraphical resolution and Declinognathodus evolution close to the Mid-Carboniferous Boundary in the Barcaliente Formation type section, NW Spain

“…Evolutionary scheme of several D eclinognathodus species based on phylogenetic relationships proposed by Sanz‐López et al . () and Sanz‐López & Blanco‐Ferrera () around the M id‐ C arboniferous B oundary in the B arcaliente F ormation type section. A, DGO 15086 (holotype) from sample MILL ‐13 F ; B, DGO 15088 from sample MILL ‐14; C–E, DGO 15383, 15387 and 15386 from sample BAR ‐13; F, DGO 15423 from sample BAR ‐23; G, DGO 15389 from sample BAR ‐13; H, DGO 15424 from sample BAR ‐23; I,J, DGO 15428 and 15429 from sample BAR ‐24; K–M, DGO 15357–15359 from sample BAR ‐11; N–P, DGO 15404, 15403 and 15406 from sample BAR ‐20; Q, DGO 15407 from sample BAR ‐21; R, DGO 15402 from sample BAR ‐20; S, DGO 15416 from sample BAR ‐21; T–U, DGO 15432–15433 from sample BAR‐24.…”

“…C–G) appear in the upper part of the D. bernesgae Zone, between 139 and 147 m above the base of the Barcaliente Formation in the type section (samples BAR‐11 to BAR‐15). Specimens of the two‐first taxa found are early morphotypes of those species transitional from D. bernesgae (Sanz‐López & Blanco‐Ferrera ; Fig. ).…”

“…). Recently, Sanz‐López & Blanco‐Ferrera () described several morphotypes of the D. noduliferus group along one hundred metres in the Barcaliente Formation type section. The specimens studied and illustrated are stored in the repository of the Museum of Geology at the University of Oviedo, Spain (abbreviated DGO).…”