Late–Early Miocene) at the Atlantic Coast of Patagonia, Argentina
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Palaeogeography, Palaeoclimatology, Palaeoecology 292 (2010) 507–519 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo A baseline paleoecological study for the Santa Cruz Formation (late–early Miocene) at the Atlantic coast of Patagonia, Argentina Sergio F. Vizcaíno a,b,⁎, M. Susana Bargo a,b, Richard F. Kay c, Richard A. Fariña d, Mariana Di Giacomo d, Jonathan M.G. Perry e, Francisco J. Prevosti f, Néstor Toledo a,b, Guillermo H. Cassini a, Juan C. Fernicola g a División Paleontología de Vertebrados, Museo de La Plata, Paseo del bosque s/n, B1900FWA, La Plata, Argentina b CONICET-CIC, Argentina c Department of Evolutionary Anthropology, Duke University, Box 90383, Durham, NC 27705, USA d Sección Paleontología, Facultad de Ciencias, Universidad de al República, Iguá 4225, 11400 Montevideo, Uruguay e Department of Anatomy, Midwestern University, 555 31st St., Downers Grove, IL, 60515, USA f División Mastozoología , Museo Argentino de Ciencias Naturales “Bernardino Rivadavia,” Buenos Aires, Argentina g División Paleontología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia,” Buenos Aires, Argentina article info abstract Article history: Coastal exposures of the Santa Cruz Formation (late–early Miocene, southern Patagonia, Argentina) between Received 13 January 2010 the Coyle and Gallegos rivers have been a fertile ground for recovery of Miocene vertebrates for more than Received in revised form 15 April 2010 100 years. The formation contains an exceptionally rich mammal fauna, which documents a vertebrate Accepted 18 April 2010 assemblage very different from any living community, even at the ordinal level. Intensive fieldwork Available online 27 April 2010 performed since 2003 (nearly 1200 specimens have been collected, including marsupials, xenarthrans, notoungulates, litopterns astrapotheres, rodents, and primates) document this assertion. The goal of this Keywords: study is to attempt to reconstruct the trophic structure of the Santacrucian mammalian community with Carnivore guild Herbivore guild precise stratigraphic control. Particularly, we evaluate the depauperate carnivoran paleoguild and identify Vertebrate paleontology new working hypotheses about this community. A database has been built from about 390 specimens from Paleoecology two localities: Campo Barranca (CB) and Puesto Estancia La Costa (PLC). All species have been classified as Population density herbivore or carnivore, their body masses estimated, and the following parameters estimated: population Basal metabolism density, on-crop biomass, metabolic rates, and the primary and secondary productivity. According to our results, this model predicts an imbalance in both CB and PLC faunas which can be seen by comparing the secondary productivity of the ecosystem and the energetic requirements of the carnivores in it. While in CB, the difference between carnivores and herbivores is six-fold, in PLC this difference is smaller, the secondary productivity is still around three times that of the carnivore to herbivore ratio seen today. If both localities are combined, the difference rises to around four-fold in favour of secondary productivity. Finally, several working hypotheses about the Santacrucian mammalian community and the main lineages of herbivores and carnivores are offered. © 2010 Elsevier B.V. All rights reserved. 1. Introduction between the rivers Coyle and Gallegos, bears an exceptionally rich fauna that documents an assemblage very different from any living 1.1. Background mammalian community. These localities are situated at about 52 degrees South latitude, barely 100 km from the Strait of Magellan The Santa Cruz Formation (late–early Miocene) cropping out on (Fig. 1). Many collections of fossil vertebrates were made in this the Atlantic coast of southernmost continental Patagonia, Argentina, region in the nineteenth century beginning with the efforts of the Ameghino brothers in 1891–1892 and later by J. B. Hatcher's group (see Marshall, 1976). Extensive anatomical descriptions and illustra- ⁎ Corresponding author. División Paleontología de Vertebrados, Museo de La Plata, Paseo del bosque s/n, B1900FWA, La Plata, Argentina. Tel.: +54 221 425 9161x129, 38; tions of these fossils are available in the Reports of the Princeton fax: +54 221 425 7527. University Expeditions to Patagonia edited by W.B. Scott between E-mail addresses: [email protected] (S.F. Vizcaíno), 1900 and 1932 (see Scott, 1903–1905, 1910, 1912, 1928, and Sinclair, [email protected] (M.S. Bargo), [email protected] (R.F. Kay), 1906, 1909). [email protected] (R.A. Fariña), [email protected] (M. Di Giacomo), Few further systematic efforts to collect here were made before the [email protected] (J.M.G. Perry), [email protected] (F.J. Prevosti), [email protected] (N. Toledo), [email protected] (G.H. Cassini), work of A. Tauber. This author (Tauber, 1997a,b) surveyed the geology [email protected] (J.C. Fernicola). of the Santa Cruz Formation south of Coy Inlet, reidentified the most 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.04.022 508 S.F. Vizcaíno et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 292 (2010) 507–519 S.F. Vizcaíno et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 292 (2010) 507–519 509 productive fossil sites and levels, and made important collections faunas from the early to middle Miocene Santacrucian Age: Tauber (mostly housed at the Museo de Paleontología, National University of (1997a) Protypotherium attenuatum and Protypotherium australe Córdoba, Argentina). Tauber recorded about 60–70 species from 27 Biozones. He found them to be very similar, suggesting that no en- fossiliferous levels (FLs) in this region and identified two Biozones: vironmental characteristics distinguish them. Although usually in- the Protypotherium attenuatum Zone and the Protypotherium australe terpreted as a “mixed” habitat due to the presence of at least one Zone (Tauber, 1997a,b, 1999; Krapovickas et al., 2008; see below, arboreal primate (Homunculus) in addition to many (supposed) Geological Framework). Other researchers (e.g. Bown and Fleagle, savanna-adapted mammals, the cenogram statistics suggest the area 1993) made extensive collections of Santa Cruz Formation mammals was wetter and less open than previously thought (e. g., Pascual and farther north in Santa Cruz Province but did not collect south of Coy Ortiz-Jaureguizar, 1990). The lack of differentiation between the two Inlet. faunas is notable because it contrasts with the suggestion of Tauber Since 2003, intensive fieldwork performed by our team, in the (1997b, 1999) (based on various lines of faunal evidence) that the costal localities between the Gallegos and Coyle rivers, has confirmed climate had become less humid and more “open,” that is with fewer Hatcher's impressions of more than 100 years ago, especially at the trees, during this interval. If anything, the analysis of Croft (2001) site of Corriguen Aike (Puesto Estancia La Costa, Tauber, 1997a,b): this suggests slightly greater rainfall in the upper (P. australe) zone as is the richest assemblage of pre-Pleistocene mammalian skulls and indicated by the slope of the medium-sized mammals. Another articulated skeletons (Fig. 2) known on the continent (Hatcher, 1903). observation of the study of Croft (2001), was the “depauperate nature At present, nearly 1200 specimens have been collected by our group. of the carnivore palaeoguild in South America” prior to the Great Marsupials, including marsupials, xenarthrans, several South Amer- American Biotic interchanges (Croft, 2001: 283), with only one and ican ungulate lineages (notoungulates, litopterns and astrapotheres), two mammalian predators in the P. attenuatum and P. australe zones rodents, and primates constitute the main mammalian taxa present. respectively. Among birds, the phorusrhacoids are worth noting. Fariña (1996) provided a different approach to analyzing mam- Some work has been undertaken in the past to reconstruct aspects malian palaeocommunity structure using a general ecological rela- of the paleoecology of the Santa Cruz Formation based on the tionship between population density and body size (Damuth, 1981, composition of the mammalian remains. In a landmark paper, Pascual 1987, 1991). Since body size has long been known to be related to and Ortiz-Jaureguizar (1990) examined faunal change among South basal metabolic rate (Kleiber, 1932; McNab, 1980, Peters, 1983), American Cenozoic mammals based on the percentages of herbivo- Fariña (1996) assessed the abundance of herbivorous and carnivorous rous species with different crown heights. As chronologic units they mammals larger than 10 kg listed for the Luján Local Fauna in Tonni et used South American Land Mammal Ages. They include the Deseadan, al. (1985). The same method was used to examine the palaeoecolo- Colhuehuapian and Santacrucian mammal faunas collectively as the gical characteristics of an important mid-Pliocene faunal turnover “Patagonian faunistic cycle,” and recognize two subcycles within it — dated at ca. 3.3 Ma (Vizcaíno et al., 2004). Although this approach Deseadan and Pansantacrucian. The latter, encompasses the Colhue- rests on rather general approximations, it provides a tool to compare huapian and the Santacrucian Land Mammal Ages, representing an different extinct faunas to generate or identify working hypothesis to interval