CONICET | Buscador de Institutos y Recursos Humanos

Although linguliform brachiopods are a common component in the thick and continuous Upper Cambrian-Ordovician clastic successions of northwestern Argentina and Bolivia, to date they remain almost unknown. A few species from the Eastern Cordillera (Cordillera Oriental) were described and illustrated by H. J. Harrington more than eighty years ago and their taxonomic placement needs revision. Other forms have been mentioned in the context of taphonomic analyses on the ?lingulid shell beds? recorded from different localities of NW Argentina. In this study, we report wellpreserved obolids from a succession of sandstones and siltstones referred to the Humacha Member of the Santa Rosita Formation, which according to the conodonts of the Paltodus deltifer Zone is of mid Tremadocian (Tr2) age. Rhynchonelliform brachiopods are dominated by Nanorthis purmamarcensis Benedetto and Lipanorthis spp. (unpublished). Lingulate brachiopods consist of acrotretids (not included here) and two species of obolids assigned to Libecoviella Mergl and Leptembolon Mickwitz. The former is represented by a new species relatively close to Libecoviella ovata (Havlíĉek). Like other ?westoniid-like? obolids, it possesses the characteristic external sculpture of zig-zag terrace lines, which has been interpreted as an adaptation to burrowing into the substrate. Libecoviella is typical of the upper Tremadocian and Floian strata of the Prague basin (Třenice and Klabava formations, respectively) and it has been reported recently from Australia. Leptembolon has been recorded in the same Bohemian formations, but together with other taxa it forms the Thysanotos-Leptembolon Association present in Baltica (Estonia) and a series of high-latitude terranes (e.g. Alborz, Perunica, Central Iran). The record of Leptembolon and Libecoviella in the high- to temperate-latitude Central Andean region confirms the peri-Gondwanan distribution of these genera.