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Miquel and Rodriguez—Terrestrial gastropods from Santa Cruz


species of Stephacharopa Miquel and Araya 2013. Adding to the information previously published by Rodriguez et al. (2012), we describe herein a remarkable land micromollusk assemblage from the Santa Cruz Formation including a new species of Gastrocopta (Vertiginidae), ?Scolodonta (Scolodontidae), Punctum (Punctidae), Zilchogyra (Charopidae), and the new genus and species Patagocharopa enigmatica, tentatively assigned to Charopidae. Fossil land snails are useful tools for paleoclimate inter-


pretations and have been successfully studied in other areas as paleoenvironmental indicators. Particularly, terrestrial mollusks are good environmental indices and permit precise reconstruc- tions of past environments (Rousseau and Wu, 1999). Land snail assemblages have provided reliable information on tem- perature and moisture conditions, allowing identification of climatic cycles from Quaternary loess sequences at Northern (Rousseau, 1989) and Western Europe (Rousseau, 1987; Rousseau and Puisségur, 1990, 1999; Rousseau et al. 1994; among others), and Southern Asia (Rousseau andWu, 1999). The importance of these groundbreaking records from


Patagonia is significant from a paleoenvironmental standpoint. The taxonomic and distribution of the land snail communities can add independent and complementary source of evidence for habitat conditions during the Early Miocene, in support or in contrast with previous paleoenviornmental and paleoclimate settings based mainly on mammals.


Geographical and stratigraphical provenance of the fossil terrestrial shells


The outcrop where the material was collected emerges between the Coyle and Gallegos inlets, on the Atlantic coast of Patagonia in southern Santa Cruz, and belongs to the Rousseau Santa Cruz Formation, of continental origin. This formation is exposed at many places in the eastern portion of southern Extra-Andean Patagonia (Russo et al. 1980; Fig. 1.1, 1.2) and was deposited during the late Burdigalian/early Langhian, as conceived in the International Stratigraphic Chart (between 18 and 15 Myr.; Marshall et al. 1986). The Santa Cruz Formation can be divided into two members, i.e. the Estancia La Angelina Member and the underlying Estancia La Costa Member. The materials described herein were recovered from a stratum of volcanic ashes within the Estancia La Costa Member. This member is 120m thick and characterized by predominantly greenish epiclastic claystones, chonites, and limolitic sandstones, with mature and immature paleosols and low-sinuosity paleochan- nels (Tauber, 1994). According to Tauber (1999), there are 21 distinct fossiliferous levels. However, subsequent work by Fleagle et al. (2012) and Perkins et al. (2012) suggests that the lowest seven levels identified by Tauber (1997a) are a single sequence repeated at other northern coastal localities of the Santa Cruz Formation and that there is no temporal difference between them. Accordingly, a rectified age for PLC (paleonto- logical site Puesto de la Estancia La Costa) sequence is estimated between 16.4 and 17.5 Myr. Yet, in this work the designation of the fossiliferous levels follows the nomenclature and the stratigraphical profile of Tauber (1999; Fig. 2) for ease of identification.


749 The material studied was collected at the paleontological


site ‘Puesto de la Estancia La Costa’ (=Corriguen Aike; PLC: 51° 12’ 8,2” S and 69° 03’ 35,6” W; Fig. 1.1, 1.2). The bed yielding the fossil material is Tauber’s fossiliferous Level 6 (Fig. 2), which consists of a brownish massive cineritic tuff, settled as a pyro-arenite layer. This level is distinguished by a significant amount of relatively complete skeletal remains of mammals and birds, and coprolites appearing at the exposed beds on the intertidal zone during low tide. The lithogenetic characteristics of the fossil-bearing rocks suggest low paleoto- pographic environments in proximity to floodplains, where the humidity input was high to moderate (Tauber, 1994).


Materials and methods


The analyzed sample consisted of approximately 720dm3 of sedimentary rock. Land snail specimens were identified by washing and screenings through a series of mesh sizes down to 200 µm. The fraction retained was examined under a stereo microscope, with specimens retrieved by ‘picking’ with fine forceps. After metal-coating, specimens were imaged with a Scanning Electron Microscope (Philips XL 30 TMP) at the Servicio de Microscopía Electrónica de Barrido of the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Buenos Aires. The material available for this study includes 26 fragmen-


tary specimens stored in the collection of the Museo Regional Provincial ‘Padre Manuel Jesús Molina’ (MPM), in the city of Río Gallegos (Santa Cruz Province, Argentina). Additional specimens studied were housed in the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’ (MACN, Buenos Aires, Argentina). The taxonomic classification we follow is that of Bouchet


and Rocroi (2005). Systematic paleontology


Superfamily Pupilloidea Turton, 1831 Family Vertiginidae Fitzinger, 1833 Subfamily Gastrocoptinae Pilsbry, 1918 Genus GastrocoptaWollaston, 1878


Type species.—Pupa acarus Benson, 1856, by subsequent designation of Pilsbry (1916).


Occurrence.—Both extant and fossil representatives of the genus Gastrocopta are known on the basis of records from extensive areas of the American continent, as well as the Galapagos Archipelago (Miquel and Herrera, 2014), but no living or fossil species has been recorded for Chile (Stuardo and Vega, 1985). Paleocene–Recent (Salvador and Simone, 2013).


Occurrence in Argentina.—Modern records indicate its occur- rence from temperate and tropical regions of the north and central areas of the country down to the area over northern Patagonia, approximately at 34°S (Hylton Scott, 1963, 1968). Doering (1881) reported it from the banks of the Colorado River, in northern Patagonia. The new species described herein


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