Lingulida (Brachiopoda) from the Early Permian of Argentina

ARCHBOLD, N.W.; CISTERNA, G.A.

La Plata

Simposio; III Simposio Argentino del Paleozoico Superior; 2003

Representatives of the Lingulida (usually referred to as inarticulate brachiopods) have been widely recorded from the Late Palaeozoic of Argentina as summarised in the two volumes edited by Archangelsky (1987, 1996). Most of the records of these brachiopods are from localities and stratigraphical formations that are now regarded as being of Early Permian (Asselian ? Sakmarian) age. Previous records have referred these brachiopods to the genera Orbiculoidea and Lingula. We describe and figure representatives of the two genera from the strata of the Santa Elena Formation corresponding to the "Tramojo Serie" defined by Keidel (1939). This stratigraphical unit is located on the west flank of the Uspallata Hill, in the SW extreme of the Precordillera in the Uspallata area, Mendoza province. From the biostratigraphical viewpoint, the upper part of the Santa Elena Formation is characterized by the presence of the Costatumulus amosi Biozone (Taboada, 1998). However, inarticulate brachiopods studied herein appear in the lower part of this unit; they are placed to the base of a stratigraphical interval about 10 meters thick, which is essentially composed of black mudstones with calcareous concretions. This interval, located immediately above of bed carrying a floral fossil assemblage approximately equivalent to the NBG biozone (Nothorhacopteris-Botrychiopsis-Ginkgophyllum) , could be representing a first flooding marine event inside of this sequence. This horizon suggests the beginning of the marine conditions which have been interpreted by some authors (Archangelsky, A. & Archangelsky, S., 1987) like a shallow marine environment. Also, we can consider that the Lingulida occurrence indicates shallow water, transgressive conditions, possibly with salinity of not always normal levels. We note that several species of Orbiculoidea have been described and illustrated from the Early Permian of Argentina by authors such as Reed (1927), Feruglio (1934) based on an illustration by Fossa Mancini (1933), and Antelo (1972). The so-called Lingula reports from Argentina have never been accompanied by illustrations. Study of the new specimens herein have revealed that they are not true Lingula. While being allied to genera such as the Permian Semilingula (Popov,1990), Carboniferous to Cretaceous Lingularia (Biernat & Emig, 1993), Devonian to Carboniferous Barroisella (Hall & Clarke 1892) and the Brasilian Permian Langella (Mendes, 1961),the Argentinian specimens demonstrate different dorsal internal visceral and muscular structures and hence appear to belong to a new genus.