Bivalves from the Triassic-Jurassic transition in Northern Spain (Asturias and Western Basque-Cantabrian Basin)

Abstract. Bivalve mollusks from the Triassic-Jurassic transition collected in eight localities in Asturias and the western Basque-Cantabrian Basin (Palencia province) are systematically revised. Preservation is poor at all localities. The dominant Rhaetian bivalves are Isocyprina concentrica (Moore) and Bakevellia (Bakevelloides) praecursor (Quenstedt). These species, together with Isocyprina cf. ewaldi (Bornemann), Pteromya cf. crowcombeia (Moore), Pseudoplacunopsis alpina (Winkler), and Modiolus? sp. (cf. minimus J. Sowerby), with a specimen of Arcestidae (?), belong to an assemblage similar to that found in the Westbury and Lilstock formations (Penarth Group) in the late Rhaetian of sout…