Caracterización de Choffatirhynchia nov. gen. (Brachiopoda, Rhynchonellida) en el Toarciense (Jurásico) de la Cordillera Ibérica (España)

Abstract

Se describen y caracterizan Choffatirhynchia nov. gen. y las dos especies que se incluyen en él: C. vasconcellosi (CHOFFAT in DUBAR, 1931) y C. turolensis nov. sp., discutiéndose las afinidades y diferencias de este género con otros géneros próximos, como Homoeorhynchia BUCKMAN, 1918, Rhynchonelloidea BUCKMAN, 1918, Quadratirhynchia BUCKMAN, 1918 y Globirhynchia BUCKMAN, 1918. Se precisa la distribución estratigráfica, en la Cordillera Ibérica, de C. vasconcellosi y de C. turolensis, en relación con la bioestratigrafía de detalle de dos secciones expandidas representativas del Toarciense del sector central de la cordillera (Sección de la Rambla del Salto y Sección de Ariño), en las que se han estudiado las asociaciones de ammonoideos y braquiópodos. Los datos obtenidos en la Cordillera Ibérica, junto con los proporcionados por diferentes autores en otras cuencas del Tethys Occidental, han permitido establecer la distribución paleobiogeográfica de las especies de Choffatirhynchia, que se conocen en la Península Ibérica, Sureste de Francia y Norte de África.

Choffatirhynchia nov. gen. is described and characterized, together with the two species included in the new genus, C. vasconcellosi (CHOFFAT in DUBAR, 1931) and C. turolensis nov. sp. The genus Choffatirhynchia includes medium-sized rhynchonellids, that present a subtetrahedral to globose shell, with the dorsal valve more convex than the ventral valve, a subrectangular dorsal fold, and numerous and dense ribs covering the whole shell; the beak is suberect, narrow and pronounced, with a big foramen; the areas are weak and not depressed; a narrow and shallow septalium, and raduliform crura are present. Choffatirhynchia is distinguished from Homoeorhynchia BUCKMAN, 1918 and Rhynchonelloidea BUCKMAN, 1918, taken as closest from a morphological point of view, in its wider and lower dorsal fold and denser costulation. It differs from Quadratirhynchia BUCKMAN, 1918, a genus to which C. vasconcellosi had previously been assigned occasionally, in the suberect beak and the absence of depressed planareas and squama-glotta. It is distinguished from Globirhynchia BUCKMAN, 1918, in which some species present a rimmed foramen similar to that found in C. turolensis, for having a less convex ventral valve as compared to the dorsal valve. The stratigraphical distribution in the Iberian Range of C. vasconcellosi and of C. turolensis is accurately established on the basis of the detailed biostratigraphy of two expanded sections representative of the Toarcian of the central sector of this mountain range (section of Rambla del Salto and section of Ariño), in which both ammonoid and brachiopod associations have been studied. C. vasconcellosi, the type species of the genus, is recorded in the Iberian Range in the Serpentinus Zone and in the Laticosta Subzone of the Bifrons Zone of the Toarcian. It is found in the same stratigraphic position in the Coastal-Catalan Range, in the Pyrenees, in the Balearic Islands (Minorca), in the Lusitanian Basin in Portugal and in the Middle Atlas in Morocco. C. turolensis nov. sp. is recorded in the Iberian Range from the Bifrons Zone (Bifrons Zubzone) to the Insigne Zone (Insigne Subzone) of the Toarcian; its presence in the Pyrenees and in southeastern France is also probable. C. vasconcellosi is a frequent species in the brachiopod associations that characterise the Spanish Bioprovince of brachiopods, recognised along several basins of the Western Tethys. C. turolensis nov. sp. is, on the contrary, a species of a more restricted distribution and is recorded at a time of low diversity in the whole region.