The actual status of Triassic Spinicaudatan fauna records (Crustacea:Diplostraca) in western Argentina

VAZ TASSI, L.; GALLEGO, O.F.; ZAVATTIERI, A.M.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

International Paleontological Association

The investigations of spinicaudatan group in Argentina began with Jones? contributions there in 1862 and were intensified after the 1990s, with numerous new taxa reported from different continental Triassic sedimentary sequences in western Argentina, largely in the Cuyo and Ischigualasto-Villa Unión basins and San Rafael Depocenter. The most important spinicaudatan records come from localities of the Río Mendoza-Cerro de Las Cabras and Potrerillos-Cacheuta sequences (Uspallata Group, Cuyo Basin) and from the Chañares, Ischichuca, Los Rastros and Ischigualasto formations (Agua de la Peña Group, Ischigualasto-Villa Unión Basin). All mentioned stratigraphic units represent an interval ranging from lower Middle (=Anisian) to early Upper (= Carnian) Triassic, which bears the greatest and most diverse Triassic spinicaudatan collection of Argentina. The families represented until now are: Euestheriidae (Euestheria) recorded in the Ischichuca, Los Rastros, Cerro de Las Cabras, Potrerillos and Cacheuta formations; Loxomegaglyptidae (Triasoglypta and Loxomegaglypta) from the Montaña, Ischichuca, Los Rastros, Ischigualasto, Potrerillos and Cacheuta formations; Ulugkemiidae (Triasulugkemia) known from the Ischichuca, Cacheuta and Potrerillos formations; Palaeolimnadiopseidae (Endolimnadiopsis) in the Potrerillos and Cacheuta formations and, Pemphilimnadiopseidae (Challaolimnadiopsis) from the Cerro de Las Cabras and Potrerillos formations. New findings include the first mention of three families: Fushunograptiidae (Estheriellites) recorded in both the Chañares and Cerro de Las Cabras formations; Polygraptidae (?Dendrostracus) in the Ischigualasto Formation; and Lioestheriidae (Cornia) in the Quebrada de los Fósiles Formation (Puesto Viejo Group, San Rafael Depocenter) referred to Early Triassic (Induan-Olenekian) age, constituting the oldest known species from the Triassic of South America, with affinities to Indian Permo-Triassic boundary species. Recently, an ichnofossil (Diplopodichnus?) in the Talampaya Formation (Early Triassic) (Ischigualasto Villa Unión Basin) was also found, which could be assignable to Spinicaudata and therefore indicate the presence of this group since the beginning of Triassic times. The comparisons between spinicaudatan faunas from Argentina and from other Triassic gondwanan strata (mainly Brazil, Chile, India and Australia) allow us to know the distribution of these forms, including its recovery, diversification and routes of dispersion after the Permo-Triassic extinction event. An increase in the size of the valve is observed in species from Early to Late Triassic, reflecting a trend of increasing body size for Argentinean specimens, as mentioned for other invertebrate groups. The morphologic variation and therefore the increase in the diversity of species during Triassic is evident in the spinicaudatan fauna record in Argentina, probably due to better climatic condition occurred towards the end of the Period.