First occurrence of the giant shark Carcharocles megalodon (Agassiz, 1843) (Lamniformes; Otodontidae) at Buenos Aires Province, Argentina

Carcharocles megalodon is considered a macropredatory shark that inhabited the seas around the world from middle Miocene to late Pliocene. In Argentina, it has only been formally recorded at two localities. Here, we report the first record for this taxon in the Buenos Aires Province. This occurrence is based on an isolated tooth recovered on the beach at the Punta Médanos locality, which lacks clear stratigraphic context. Based on the regional geology, the specimen probably came from Pliocene beds. Its size indicates that it probably belongs to a juvenile individual. Keywords: Carcharocles megalodon, macropredatory shark, fossil teeth, Mar de Ajó.

Himalayites treubi DOUVILLE (1912), Fósil índice de Titoniano Superior en el sur-oeste del lago Titicaca, Puno; implicaciones bioestratigráficas.

RESUMEN Con motivo de la actualización de la geología regional del Cuadrángulo de Puno (32v) a escala al 50,000, se han desarrollado diversas labores de campo, como ésta contribución que documenta nuevos resultados de rocas mesozoicas del Grupo Yura en las inmediaciones del Distrito de Tiquillaca, (al SO del Lago Titicaca), tales afloramientos solían asignarse a rocas jurásicas del Grupo Lagunillas. El afloramiento en estudio se halla en el Cerro Yana Apacheta, en cuya quebrada principal se elaboró una columna estratigráfica y el perfil correspondiente en el que se encontró el amonite Himalayites treubi DOUVILLE (1912), estableciendo una correlación con las formaciones Chachacumane y Labra. El taxón se describe con base en cinco ejemplares y sus parámetros estándares de tasa de enrollamiento y ornamentación del costillaje. Se considera que el hallazgo de amonites del Tithoniano en el Cuadrángulo 32v amplía y documenta la columna previamente reportada para la localidad y establece una clara correlación con sedimentos del sur de Asia (Indonesia). ABSTRACT On the occasion of the updating of the regional geology of the Puno Quadrangle (32v) at 50,000 scale, several field works have been developed, such as this contribution that documents new results of Mesozoic rocks of the Yura Group in the vicinity of the Tiquillaca District, (SW of Lake Titicaca), such outcrops used to be assigned to Jurassic rocks of the Lagunillas Group. The outcrop under study is located in Cerro Yana Apacheta, in whose main gorge a stratigraphic column and the corresponding profile was elaborated, in which the ammonite Himalayites treubi DOUVILLE (1912) was found, establishing a correlation with the Chachacumane and Labra formations. The taxon is described based on five specimens and its standard parameters of coiling rate and rib ornamentation. The finding of Tithonian ammonites in Quadrangle 32v is considered to extend and document the column previously reported for the locality and establishes a clear correlation with sediments from South Asia (Indonesia).