Journal of Paleontology, 89(5), 2015, p. 748–761 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2015.66


A novel late Early Miocene assemblage of terrestrial gastropods from Santa Cruz (Patagonia, Argentina)


Sergio E. Miquel1 and Pablo E. Rodriguez2


1Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Av. Ángel Gallardo 470, Ciudad Autónoma de Buenos Aires C1405DJR, República Argentina ⟨semsnail@yahoo.com.ar⟩,


⟨semsnail@macn.gov.ar⟩ 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Cátedra y Museo de Paleontología, Sección Paleovertebrados, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Av. Vélez Sarsfield 299, Córdoba X5000JJC, República Argentina; Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Av. Vélez Sarsfield 1611, Córdoba X5016GCA, República Argentina ⟨pabloem.rodriguez@gmail.com⟩


Abstract.—A remarkable fossil assemblage composed of five gastropod taxa is described from the Early Miocene of Santa Cruz (Patagonia, Argentina) in southernmost South America. The assemblage includes extinct and living genera South America, and on geographic distributions and represent background new information on spatial and across time distributions as well as identification of new taxa. A new taxon, Patagocharopa enigmatica n. gen. n. sp., is tentatively assigned to Charopidae. Gastrocopta patagonica n. sp. (Vertiginidae) represents the oldest record of Gastrocopta in Argentina and the southernmost record for the Americas. Punctum patagonicum n. sp. (Punctidae) represents the first record of Punctum for continental South America, and characterized by a protoconch with traces of axial costulae and a teleoconch with strong radial ribs. Zilchogyra miocenica n. sp. is the first Miocene record of the charopid genus Zilchogyra. Fragments of a possible Scolodonta (Scolodontidae) are recorded. Overall, the assemblage represents an important and useful paleoenvironmental tool. This fauna suggests that a more temperate and humid environment than today—with a more dense vegetation cover—was prevalent at this site during the Early Miocene.


Introduction


Patagonia is a region of great biogeographical interest because of its paleogeographical history and the endemic nature of its current biota. On this regard, Santa Cruz province in southern Patagonia harbours fossiliferous sites of extraordinary abundance and diversity of unique plants and animals. This is particularly true for the Santa Cruz Formation (Early Middle Miocene), which covers areas of eastern Austral Patagonian Cordillera and part of the Extra-Andean Patagonia, between Lake Buenos Aires and Río Turbio in the west, and the San Jorge Gulf and northern Tierra del Fuego in the east (Matheos and Raigemborn, 2012). Interestingly, this formation bears some of the most prolific continental deposits with fossil vertebrates of South America. These fossils have been addres- sed in many publications for over a century (Tauber, 1997a, 1997b, 1999; Vizcaíno et al., 2012; other references cited therein). The beds of the Santa Cruz Formation enclose a rich and diverse vertebrate fauna that includes mammals, birds, anurans, and reptiles; there are also insects, plant macro- and micro-remains (Tauber, 1994, 1999; Brea et al., 2012; Degrange et al. 2012; Fernicola and Albino, 2012; Krapovickas, 2012; Vizcaíno et al., 2012), coprolites (Tauber, 2005), as well as land gastropod shells (Rodriguez et al., 2012). This formation has also been highlighted as the foremost fossil-bearing deposit for


understanding the biological diversity and community structure of mammals in Patagonia prior to the Great American Biotic Interchange (Vizcaíno et al., 2012). The ‘Estancia La Costa’ Member, which is the lowermost within this formation, is the most significant in terms of specimen and taxon diversity, as well as by state of conservation of the fossils. The historical development of terrestrial mollusks studies


in Argentina is limited; a summary can be found in Parodiz (1969) and di Pasquo et al. (2008), highlighting both the surveys of Hermann von Ihering, who described a few species of large size mollusks (Strophocheilidae) (see Parodiz, 1996; Miquel and Bellosi, 2010) from the Tertiary of Patagonia around the early twentieth century. Fossil records of land micromollusks from the Patagonian


region are scarce. A unique Cretaceous record is that of Morton (1999), who recorded Radiodiscus but its taxonomy requires a re-assessment. The micromollusks from the deposits of Gran Barranca described by Miquel and Bellosi (2010) are Eocene taxa referred to Charopidae. The Strophochelidae have been recorded in Paleocene rocks (Parodiz, 1969), and in Miocene beds from the Limay River area (Collón Cura Formation, Río Negro Province) (Miquel and Manceñido, 1999). The single record of land mollusks in the Santa Cruz Formation is a Charopidae specimen initially assigned to Stephadiscus Hylton Scott 1981 (Rodriguez et al. 2012) but later re-identified as a


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