PRESENCIA DEL GENERO SIMOCOSMOCERAS SPATH (CEPHALOPODA - AMMONOIDEA) EN EL TITHONIANO ANDINO y SU SIGNIFICADO PALEOBIOGEOGRAFICO

Hector A. Leanza, Federico Oloriz

Abstract


The presence of the ammonite genus Simocosmoceras Spath (1925) in the andean Tithonian through a single specimen closely allied to S. adversum (Oppel), which is regarded as a new subspecies named S. adversum andinum n. ssp., is reported in this paper for the first time. The new taxa was found in the Vaca Muerta Formation at the classic locality of Cerro Lotena, province of Neuquén, Argentina, in sediments belonging to the P. zitteli Zone. The morphological analysis of the new subspecies allows to recognize the Plataform Effect as stated by Olóriz (1984/85). The paleobiogeographic significance of the first record of Simocosmoceras in the andean Tithonian suggests a subspeciation by colonisation of a marginal platforrn area.

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