Canales, Omar

Chavez-Hoffmeister, Martín

De Pol, Ricardo

Labarca, Rafael

Navarro-Harris, Ximena

Pino, Mario

Recabarren, Omar

Repositorio Digital Sernageomin

El sitio Pilauco, Pleistoceno tardío, Osorno, Chile .  Mario Pino 1, Ximena Navarro-Harris 2, Rafael Labarca 3 , Martín Chavez-Hoffmeister 4, Omar Recabarren 1, Patricia Canales 1 & Ricardo De Pol 5 1 Instituto de Ciencias Ambientales & Evolutivas, Universidad Austral de Chile;; 2 Departamento de Antropología, Universidad Católica de Temuco; 3 Programa de Doctorado Universidad Nacional del Centro de la Provincia de Buenos Aires; 4 University of Bristol, School of Earth Science, U..K; 5 Departamento de Oceanografía, Universidad de Concepción, ricdepol@udec.cl.  1 E-mail: mariopino@uach.cl   Resumen.  El sitio Pilauco está ubicado en la ciudad de Osorno (40º34’12’’S, 73º06’13’’W). En el Pleistoceno tardío estuvo dominado por una asociación vegetacional de parque norpatagónico, tal como Monte Verde. Se han recuperado 718 huesos de vertebrados extintos y extantes, 30 dientes y 11 coprolitos. Tafonómicamente se registran procesos de carroñeo, pisoteo y reacomodación por crecidas fluviales esporádicas. El sitio comenzó a formarse hace 13.470±35 años 14C A.P. Posteriormente se desarrolla un pantano sobre “ox-bow lake”. La turba PB-7 contiene los restos paleontológicos y arqueológicos (13.220±60 - 11.004±186 años  14C AP). Las familias de vertebrados representadas son Gomphotheriidae, Equidae, Camelidae, Cervidae, Mylodontidae, Mephitidae, Muridae y Myocastoridae. Los artefactos líticos de basalto, andesita y obsidiana que registran los humanos tempranos se encuentran solamente en algunas unidades de excavación, asociadas a altas concentraciones de huesos. Se presentan la estratigrafía, sedimentología, paleontología, arqueología y tafonomía del sitio, basado en un gran conjunto de fechas radiocarbónicas.   Palabras Claves:  norpatagonia chilena, megafauna, hombre temprano, paleontología, arqueología.   1 Introduction  In the Intermediate Depression of south-central Chie sites containing megafauna are frequently found by chance, (until today 13 sites, Recabarren 2007). Usually the only remains recovered are the molars and tusks of gomphotheres. In 1986 a company was carrying out excavations in Pilauco, a suburb of Osorno city (40°3 ’S-73°07’ W). They found megafauna bones, classified as mastodon and horse, kept today at the History Museum of Osorno. Recabarren (2007) concluded that molars and tusks of the Pilauco Gomphothere, as well as Gomphothere remains from the other 12 sites, belong to Stegomastodon platensis. An exploratory project was developed between November 2007 and November 2008, excavating 41 m2. (Pino, 2008). Today we know a) the site is located in a wetland dating from late Pleistocene - early Holocene; b) a large amount of this space (about 2 ha) was not used for house building and is then available for excavations; and c) in the site individuals from 7 mammal families were registered. Megafauna was found coexisting with extant mammals. Bird bones, pollen, diatoms and parasites were also recovered. In a new approach, “exit”, Dillehay (2008) proposed to understand cultural developments between the late Pleistocene and early Holocene analyzing the early rhythms towards social complexity. In this approach, the emphasis is given to site location studies, paleo-faunal and -floral studies, seasonality, mobility and sedentism, and principles of organization”. Our work, till in a primary phase, is towards this direction.  2 Results  2.1 Stratigraphy, Sedimentology and Age  It is possible to recognize two geomorphologic units, each one with their own sets of beds. To the north the sit  i  limited by hills deposited by a major acid to intermediate volcanic Andean regional activity. These volcanic processes deposited a series of volcanoclastic flows, grouped under “Secuencia piroclástica – epiclástica San Pablo” (Pérez et al., 2003).  The age of this unit is equivalent to the Valdivia interglacial. In Pilauco six beds compose the hill. The PB-1 to PB-6 layers correspond to volcaniclastic and terrigenous sediments (Fig. 1). To the south of the hill four sedimentary beds originated a floodplain. Over the eroded and channelized top of PB-1 bed, well-sorted coarse gravel originate PB-6 layer. Above these PB-7, -8 and -9 layer are located, forming well-defined horizontal strata. The first two are composed by peat including gravel clasts (mode 2-3 cm diameter, 0.5 - 16%) dispersed in a fine matrix (sand 13.4 – 36.9%; mud 33.1 - 53.4% and 11 - 32% total organic carbon mater).  This kind of texture can originate in a swamp that s developed over a former ox-bow lake invaded sporadically by river overfloods. No percussion marks were found i  the aphanitic basalts, which is a typical indicator of high-velocity energy and impact.  The fossils of mammalian fauna and birds are associated exclusively to the PB-7 layer, dated between 13.220 ± 60 and 11,122  ± 178 years B.P. The pure peat PB-9 layer seals the site.   2.1 Record of vertebrates  Gomphotheriidae bones are the most abundant identified vertebrate remains. The specimens found in 1986 correspond to a left hemimandible with m2 and m3 inserted, a right hemimandible with m3 inserted, an 731isolated m2, a right humerus, three thoracic vertebra , a partial spinous process, and a fragment of skin. During the 2007-2008 campaign were obtained mostly vertebrae, the atlas, ribs, two scapulae, and pelvic elements. During the 2010-2011 season, a high concentration of elements be was found. Ribs exhibit the highest abundance. A tibia, tarsal, vertebrae, molars and a skull were also excavated. I  is worth noting that small tusk fragments were found i the surrounding grid squares, which suggests a high degree of fragmentation or shattering. The finding of a second atlas confirms the presence of at least two individuals in the deposit. After Recabarren (2007) the Chilean Gomphotheriidae remains registered south of 39º30’, including the Pilauco specimens, and classified them as Stegomastodon. platensis based on molar measurements following Alberdi and Prado (1995) and Frassinetti and Alberdi (2005) taxonomic proposal. Ungulates are the second most abundant mammal remains found in the Pilauco site, represented by the families Equidae, Camelidae and Cervidae. The horse record of the site includes 15 specimens attributed possibly to Equus (Amerhippus) andium (Recabarren et al., 2011), belonging to at least three individuals. These are the southernmost records for the genus Equus, which expands its distribution from 38º S to 40º S in the Chilean territory. Camelids are locally represented by skeletal and dental remains including a metatarsal and metacarpal shaft, a astragalus, a fragment of tibia, an isolated canine tooth, and a coxal. The fossils are temporarily assigned to cf. Hemiacuhenia paradoxa Gervais & Ameghino 1880 (Labarca and Pino, 2010). Hemiauchenia has not been recorded previously in Chile.  An isolated vertebra is the only available record of Cervidae in the Pilauco site (Fig. 2). A detailed morphological comparison with anatomical elements of various representatives of the family suggests thate specimen belongs to Pudu puda, the only confirmed record of this species for the Pleistocene (González et al., unpublished results).  Xenarthra is represented by isolated 11 sloths osteoderms. These dermal ossicles allow by first time confirmation of the presence of this group in the region. An isolated cranium belonging to the genus Conepatus represents the carnivores. This is the first fossil record of the family Mephitidae for the Pleistocene in Chile (González et al., 2010). Recently, an isolated molar with a highly worn crown has also been registered. The morphology of the molar discards the assignation to the herbivores described in the site (Aguilera et al., 2011). According to the authors the molar presents considerabl  degree of wear on its occlusal surface, therefore it is not possible to recognize the metacones and paracones. Aguilera et al. (2011) assigned the molar to Ursidae indet.  The presence of rodents is limited to two taxa. Dental pieces confirm the presence of the genus Myocastor (Pino, 2008). The presence of Loxodontomys micropus has also been confirmed through a cranium fragment (Canales, 2010).  Figure 1.  Schematic stratigraphy of the Pilauco site. PB-1: Lapilli tuff. PB-2: Lapilli tuff with abundant volcanic ash matrix. PB-3: Lapilli tuff with medium sand matrix. PB-4: Volcanic ash. PB-5: Terrigenous coarse sand, with scattered angulr pebbles. PB-6: Gravel composed by clasts ranging from 1 to 15 cm in diameter. PB-7: Peat with very dark brown matrix (10YR 3/1) including isolated gravel clasts up to 7 cm, poorly selected. Rest with erosion unconformity over PB-2 and PB-6. PB-8: Peat very similar to PB-7, but slightly more brown in color (2.5Y 4/2) and without fossils. PB-9: Black peat (2.5 Y 2/0). PB-7 and 8 interfinger with gravel and sand layers to the south.    2.2 Taphonomy  There are clear field evidences of extinct and extant bone elements concentrating in the PB-7 level, between 350 and 450 cm of local altitude, which is within the 14,680 and 13,029 calibrated ages. Only one small rodent and two bird fragments were obtained. No fish, amphibian or reptile remains have been found, although systematically search.  The local accumulation of large megafauna bones suggests that in PB-7, characterized by fine and organic textures, there was no fluvial displacement of the carcass. This is in accordance with the relative anatomical consistency of some bones (e.g. atlas and skull). An initial study of the marks on the bones of mammals has been performed. At least four types of modifications were possible to detect: carnivore marks, roots, trampling and abrasion (i.e. Labarca, 2009). Trampling marks are the most abundant and are characterized for being mainly superficial, with irregular sides, winding forms and random orientations. Such marks are registered both on gomphotheres as ungulates bones. Carnivore marks concentrated exclusive y on gomphotheres bones. The abrasion marks have been observed up to now only in the bones of camelids. High buoyancy of small and pneumatic bones could explain the absence of remains of small animals. Another explanation is related to the acidic pH of the swamp water and peat, were the thin calcareous material can be dissolved. Predators could also have played a role in the distribution of body parts often seen on the site, consuming small bones and / or moving anatomical units into their burrows (i.e. Martin, 2008). This scenario, however, does not explain the absence of other large anatomical units of 732gomphothere in the site, such as tusk, humerus and femurs. Considering the human presence on the site, actually it is not possible discard the possibility of selective transport of anatomical units by hunter-gatherers to other areas.   2.3 Archaeology  The Pleistocene human population that inhabited the Pilauco region, within a north Patagonian park landscape, must have felt attracted by the presence of an enclave rich in resources located in an ecotone of hills, floodplains and swamps. The archaeological analysis has allowed us to isolate a total of 101 intentionally modified lithic pieces. These are represented by fine grain basalt and dacitic obsidian cores; artifacts for scraping and cutting in basalt, quartzite and dacitic obsidian with unifacial marginal trimming, and principal chipping waste material (i.e. Andrefsky, 1998). The basalt and quartzite were selct d from pebbles available in the deposits of the ancient local river. In contrast, the dacitic obsidian was collected in the volcaniclastic deposits in the northern hill. The reduced lithic collection is coherent with records from other Southern Cone and Patagonian early sites (i.e. Nuñez et al., 1994)   3 Conclusions and Discussion  The PB-7 layer containing cultural and paleontological remains in Pilauco was generated by a palustrine peatdeposition event, following the retreat of a meander of the local ancient river. The swamp received fluvial overflows in many occasions, which resulted in presence of isolated gravel in the peat matrix, within a low kinetic energy environment.  This simple stratigraphy in Pilauco, as well as the described deposition environments, is more similar to Tagua-Tagua than Monte Verde. The faunal collection present in Pilauco is consistent with the described millieu, with dominance of animals associated to open environments, presence of freshwater species and generalist species. Extant and extinct taxa overlap. The cultural evidence presented in this study, show a group of generalized foragers using energy saving adtechnological strategies for the provision and production of lithic resources. The geomorphological context of the site opens the possibility to use it as prospective model in central and south Chile.  Acknowledgments  This scientific contribution was partially supported by the project FONDECYT 1100555. Thank to all Pilauco team.  References  Aguilera, F.; Chávez, M; Pino, M. 2011. Análisis de un molar perteneciente a la megafauna del Pleistoceno tardío, sitio Pilauco, Osorno, Chile. IV Congreso Latinoamericano de Paleontol gía de Vertebrados. San Juna, Argentina, Actas del Congreso, p. 88.  Alberdi, M.T., Prado, J L. 1995. Los mastodontes de América del Sur, In: M.T. Alberdi, G. Leone & E.P. Tonni (Eds.). Evolución biológica y climática de la Región Pampeana durante los últimos 5 millones de años. Un ensayo de correlación con el Mediterráneo occidental, Monografías, Museo Nacional de Ciencias Naturales, CSIC, Madrid. pp. 277-292.   Andrefsky, W. 1998. Lithics. Macroscopic approaches to analysis. Cambridge Manuals in Archaeology . Cambridge University Press, Cambridge. 322p.  Canales, P. 2010. Identificación de roedor fósil dePleistoceno Superior, sitio paleontológico Pilauco, Osorno, Chile. Unpublished Tesis, Licenciado en Ciencias Biológicas, UACH 68 p.   Frassinetti, D., Alberdi, M. T. 2005. Presencia del género Stegomastodon entre los restos fósiles de mastodontes de Chile (Gomphotheriidae), Pleistoceno Superior. Estudios Geológicos, 61: 101-107.   González, E., Prevosti, F., Pino M. 2010. Primer registro de Mephitidae (Carnivora: Mammalia) para el Pleistoceno de Chile. Magallania, 38(2): 239-248.  González, E., Labarca, R., Chávez, M. Pino. Unpublished results. First fossil record of the smallest deer Pudu puda Molina 1792 (Artiodactyla, Cervidae) in the late Pleistocene of South America.   Labarca, R. 2009. El yacimiento paleontológico "Kamac Mayu": tafonomía y procesos de formación en el Cuaternario kárstico de la cuenca de Calama (Región de Antofagasta-Chile). Ameghiniana 46 (1): 3-16.  Labarca, R., Pino, M. 2010. Nuevos antecedentes sobre l s Lamini fósiles (Artiodactyla: Camelidae) del Pleistoceno Superior en el extremo sur de Chile (30º-42ºS). Resúmenes, II Simposio Paleontología en Chile (Concepción). p. 67.   Martin, F.M. 2008. Bone crunching felids at the end of the Pleistocene in Fuego-Patagonia, Chile. Journal of Taphonomy 6 (3-4): 337-372.  Nuñez, L.; Varela, J.; Casamiquela, R.; Schiappacasse, V.; Niemeyer, H., Villagrán, C. 1994. Cuenca de Taguatagua en Chile: el ambiente del Pleistoceno superior y ocupaciones humanas. Revista Chilena de Historia Natural, 67: 503-519.  Perez, Y., Milovic, J., Troncoso, R., Hanish, F., Helms, F., Toloczky, M. 2003. Geología para el ordenamiento territorial: Área de Osorno, Región de los Lagos. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, Serie Geológica Ambiental Nº6, 62 p, 7 mapas escala 1:100.000. Santiago.  Pino, M. 2008. Pilauco, un sitio complejo del Pleistoceno tardío. Osorno, norpatagonia chilena. Universidad Austral de Chile. Valdivia, Chile.– Imprenta América. 164p.   Recabarren, O. 2007. Análisis de restos óseos de gonfoterios del área comprendida entre los 39º 39' y 42º 49' S, Centro - Sur de Chile. Unpublished Tesis, Licenciado en Ciencias Biológicas, UACH. 53 pp.   Recabarren, O., Pino, M., Cid, I. 2011. New record of Equus (Mammalia: Equidae) from the Late Pleistocene of central-south Chile. Revista Chilena de Historia Natural 84: 535-542733

El sitio Pilauco, Pleistoceno tardío, Osorno Chile

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El sitio Pilauco, Pleistoceno tardío, Osorno Chile

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