Miquel and Rodriguez—Terrestrial gastropods from Santa Cruz
closed canopy forest and open habitats during the late Early Miocene. Several studies have assessed groups of vertebrates such as frogs (Calyptocephalellidae and Leptodactylidae), teiids (Tupinambis sp.), colubrids, and iguanids, whose presence suggests warm and humid environmental conditions and the occurrence of permanent lowland lakes and quiet streams in forested areas (Fernicola and Albino 2012). Other records such as birds like the falconid Thegornis (Noriega et al., 2011), and aquatic birds such as waterfowl, limpkins, spoonbills, and dar- ters, indicated the presence of seasonally flooded open areas or permanent water bodies in more forested areas, whereas phor- usrhacids and seriemidsmay have required open habitats because of their cursorial mode of locomotion (Degrange et al., 2012). Subsequently, the Late Miocene vegetation became similar to
themodern pattern,with an expansion of steppe throughout extra- Andean Patagonia and withdrawal of forests to western areas where rainfall was still abundant (Barreda and Palazzesi, 2007). Even though some degree of aridity occurred throughout
the Early Miocene, paleoenvironmental conditions shifted into a more humid context toward the latest Early Miocene (Burdiga- lian), when Neotropical floral elements become predominant again (Barreda and Palazzesi, 2007, 2010). The environment during this time slice, known as the mid-Miocene Climatic Optimum (MMOC, 17 to 15 Myr; Zachos et al., 2001), can confidently be taken to be that which prevailed when the snail-bearing layer was deposited. According to Fleagle et al. (2012), this brief geological period can also be reliably corre- lated with warm-humid tropical conditions. Thus, the wide range of suitable habitat types suggested by the land snail paleocommunities, as indicated by the terrestrial molluscan taxa of our study, support and reinforce the pre-Late Miocene warm and humid tropical paleoenvironmental and paleoclimate settings proposed previously worldwide and for Patagonia. In summary, the studied land snail assemblage includes the
following specimens and their related current habitats: (a) Gastrocopta patagonica n. sp. (Vertiginidae), oldest record of the genus for Argentina and the southernmost record for South America, inhabits temperate and tropical regions; (b) Scolodonta sp. (Scolodontidae), inhabits from tropical rain forests, to dry forests and grasslands; (c) Punctum patagonicum n. sp. (Punctidae), first mention of the genus for continental South America, inhabits ferns, under mesophytic bushes and trees; (d) Zilchogyra miocenica n. sp. (Charopidae), first record of the genus from Miocene, inhabits tropical areas of South America from mesic forests to dry and open scrublands; and
(e) Patagocharopa enigmatica n. gen and sp. (?Charopidae), first record for South America. The studied assemblage comprises taxa in part typical of
austral regions such as the punctoidean genera Zilchogyra, and Punctum (previously known in South America only from extant specimens recorded in Juan Fernández Archipelago), together with the much more widely distributed Gastrocopta. Patagocharopa enigmatica has no clear affinities to any fossil or recent South American continental molluscan faunas. Being this the first record of this type of assemblage for
South America, and considering the high significance of land and fresh-water snails for paleoenvironmental reconstructions (Rousseau et al., 1994; Rousseau and Puisségur, 1999; Rousseau and Wu, 1999; Del Río et al., 2007; Miquel and
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Bellosi, 2010), it is of major importance to emphasize the great potential of further studies of terrestrial mollusks from Patago- nia to reveal other interesting elements of the assemblages and to enhance our full understanding of the Austral Miocene paleoenvironmental evolution.
Acknowledgments
We are grateful to the Facultad de Ciencias Exactas, Físicas y Naturales of the Universidad Nacional de Córdoba for providing the research facilities required for this study. The fossil specimens were kindly provided by the Museo Regional Pro- vincial ‘Padre Manuel Jesús Molina’ of the city of Río Gallegos. We thank A. F. Tricárico of the “Servicio de Microscopía Electrónica de Barrido” (MACN) for the specimens micro- photography [PIP Conicet 0080 to SEM] and the workers of the Estancia La Costa for allowing us field exploration in their site. To G. M. Barker (Museum of New Zealand Te Papa Tongarewa and Museum Victoria of Australia) for helping with the criticisms and English grammar revision. We gratefully acknowledge the financial support of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Authors are exclusively responsible for the views herein expressed.
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