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38
LATE–EARLY MIOCENE FOSSIL MAMMALS OF THE PAMPA GUADAL AREA,
MESETA COSMELLI, AYSÉN REGION, CHILEAN PATAGONIA.
(Mamíferos fósiles del Mioceno Temprano-Tardío del área de Pampa Guadal, meseta Cosmelli,
Región de Aysén, Patagonia Chilena)
Bostelmann, J.E.1, and Buldrini, K.E.2
1 Museo Nacional de Historia Natural, CC. 399, 11.000. Montevideo, Uruguay.
2 Laboratorio de Zoología de Vertebrados, Facultad de Ciencias, Universidad de Chile. Las Palmeras 3425.
Santiago, Chile
INTRODUCTION
Pansantacrucian faunas (Colhuehuapian through Santacrucian South American Land Mammal
Ages, SALMAs) are common components of all continental Neogene sequences of Chile and
among the most numerous and well described faunal units in South America (Ameghino, 1906;
Marshall et al., 1983). In the mountains near Puerto Guadal, south of Lake General Carrera
(Aysén Region), a large Cenozoic sedimentary basin known as the Meseta Cosmelli includes
well exposed Neogene marine and continental synorogenic clastic sequences (Fig. 1). Its upper
levels are formed by a ~1000 m thick succession of continental Miocene deposits in which
numerous fossil mammal-bearing localities have been identified (Niemeyer, 1975; Flynn et al.,
2002; De la Cruz and Suárez, 2006). The most important of these is Pampa Castillo, in the
southeastern portion of the Meseta, in which Flynn and associates collected a diverse vertebrate
assemblage during the late eighties (Flynn et al., 2002). Detailed descriptions of the fossil
mammals of Pampa Castillo are still pending, but the proposed taxonomic diversity of 36
species represents one of the highest ever recorded for any South American Early Miocene local
fauna (Flynn et al., 2002). A second locality on the northwestern half of the Meseta, known as
Pampa Guadal, has yielded beautifully preserved new specimens, making it one of the most
promising localities for Neogene land mammal studies in Chile.
Pampa Guadal is a ~3 km long and 1 km wide mesa with small streams that expose the deposits
along narrow valleys. The synorogenic Miocene continental strata have a thickness of almost
300 meters in their western exposure, transitionally overlying the marine sandstones of the
Guadal Formation. The sedimentary sequence is mostly formed by alternating chocolate-brown
siltstones and limestones, grey, brown, and greenish fine to coarse-grained sandstones, and
channelized conglomerates (Niemeyer, 1975; De la Cruz and Suárez, 2006; Fig. 2). The formal
assignation of these strata is not yet resolved, since local and regional correlations to presently
named regional lithostratigraphic units are still unclear (see discussion in Flynn et al., 2002),
and the proposed name of “Pampa Castillo” Formation was not adequately defined or justified
by Scalabrino et al. (2009). The continental sedimentation indicates a low energy fluvial
environment with point-bars, crevasse splays and levee deposits, typical of high sinuosity
meandering rivers migrating over their adjacent floodplains (Niemeyer, 1975; De la Cruz and
Suárez, 2006; Bostelmann, pers. observ.). Previously recorded fossils from this area were listed
by De la Cruz and Suárez (2006) and include a diversity of ungulates, glyptodonts and rodents.
Fossil Nothofagus leaves, trunks, and freshwater bivalves of the genus Diplodon sp. have also
been reported from nearby localities. The new vertebrate fossil material was recovered at the top
of Pampa Guadal, in mostly chestnut-brown, massive and consolidated sandstones.
FIGURE 1. Location map of the study area
showing the Meseta Cosmelli, Lake General
Carrera, and the Pampa Guadal (circle) and
Pampa Castillo (triangle) localities.
Figure 2. East-northeast view of
the characteristic synorogenic
sedimentary strata exposed at
Pampa Guadal.
MATERIALS AND METHODS
Field campaigns were conducted during March 2011 and February - March of 2012. The first
exploration aimed to assess the Guadal area and adjacent localities and to make detailed
observations on the geology and stratigraphy along the Meseta Cosmelli. In Pampa Guadal,
local investigations were carried out to evaluate its paleontological potential and collect surface-
39
LATE–EARLY MIOCENE FOSSIL MAMMALS OF THE PAMPA GUADAL AREA,
MESETA COSMELLI, AYSÉN REGION, CHILEAN PATAGONIA.
(Mamíferos fósiles del Mioceno Temprano-Tardío del área de Pampa Guadal, meseta Cosmelli,
Región de Aysén, Patagonia Chilena)
Bostelmann, J.E.1, and Buldrini, K.E.2
1 Museo Nacional de Historia Natural, CC. 399, 11.000. Montevideo, Uruguay.
2 Laboratorio de Zoología de Vertebrados, Facultad de Ciencias, Universidad de Chile. Las Palmeras 3425.
Santiago, Chile
INTRODUCTION
Pansantacrucian faunas (Colhuehuapian through Santacrucian South American Land Mammal
Ages, SALMAs) are common components of all continental Neogene sequences of Chile and
among the most numerous and well described faunal units in South America (Ameghino, 1906;
Marshall et al., 1983). In the mountains near Puerto Guadal, south of Lake General Carrera
(Aysén Region), a large Cenozoic sedimentary basin known as the Meseta Cosmelli includes
well exposed Neogene marine and continental synorogenic clastic sequences (Fig. 1). Its upper
levels are formed by a ~1000 m thick succession of continental Miocene deposits in which
numerous fossil mammal-bearing localities have been identified (Niemeyer, 1975; Flynn et al.,
2002; De la Cruz and Suárez, 2006). The most important of these is Pampa Castillo, in the
southeastern portion of the Meseta, in which Flynn and associates collected a diverse vertebrate
assemblage during the late eighties (Flynn et al., 2002). Detailed descriptions of the fossil
mammals of Pampa Castillo are still pending, but the proposed taxonomic diversity of 36
species represents one of the highest ever recorded for any South American Early Miocene local
fauna (Flynn et al., 2002). A second locality on the northwestern half of the Meseta, known as
Pampa Guadal, has yielded beautifully preserved new specimens, making it one of the most
promising localities for Neogene land mammal studies in Chile.
Pampa Guadal is a ~3 km long and 1 km wide mesa with small streams that expose the deposits
along narrow valleys. The synorogenic Miocene continental strata have a thickness of almost
300 meters in their western exposure, transitionally overlying the marine sandstones of the
Guadal Formation. The sedimentary sequence is mostly formed by alternating chocolate-brown
siltstones and limestones, grey, brown, and greenish fine to coarse-grained sandstones, and
channelized conglomerates (Niemeyer, 1975; De la Cruz and Suárez, 2006; Fig. 2). The formal
assignation of these strata is not yet resolved, since local and regional correlations to presently
named regional lithostratigraphic units are still unclear (see discussion in Flynn et al., 2002),
and the proposed name of “Pampa Castillo” Formation was not adequately defined or justified
by Scalabrino et al. (2009). The continental sedimentation indicates a low energy fluvial
environment with point-bars, crevasse splays and levee deposits, typical of high sinuosity
meandering rivers migrating over their adjacent floodplains (Niemeyer, 1975; De la Cruz and
Suárez, 2006; Bostelmann, pers. observ.). Previously recorded fossils from this area were listed
by De la Cruz and Suárez (2006) and include a diversity of ungulates, glyptodonts and rodents.
Fossil Nothofagus leaves, trunks, and freshwater bivalves of the genus Diplodon sp. have also
been reported from nearby localities. The new vertebrate fossil material was recovered at the top
of Pampa Guadal, in mostly chestnut-brown, massive and consolidated sandstones.
FIGURE 1. Location map of the study area
showing the Meseta Cosmelli, Lake General
Carrera, and the Pampa Guadal (circle) and
Pampa Castillo (triangle) localities.
Figure 2. East-northeast view of
the characteristic synorogenic
sedimentary strata exposed at
Pampa Guadal.
MATERIALS AND METHODS
Field campaigns were conducted during March 2011 and February - March of 2012. The first
exploration aimed to assess the Guadal area and adjacent localities and to make detailed
observations on the geology and stratigraphy along the Meseta Cosmelli. In Pampa Guadal,
local investigations were carried out to evaluate its paleontological potential and collect surface-
40
exposed fossil materials. The 2012 campaign focused on expanding these observations and
continuing the rescue of the abundant skeletal elements. All specimens were found on the top of
the mesa, where they were partially or completely exposed at the surface, so that their
stratigraphic position was recorded whenever possible. The materials were transported to the
National Monuments Council and then to the vertebrate paleontology collection of the National
Museum of Natural History in Santiago. Detailed geological information of the area was
obtained from Chilean Geological Chart N°95 at a scale of 1:100.000 (De la Cruz and Suárez,
2006).
RESULTS
The fossil vertebrates collected include a small but interesting assemblage of well-preserved
mammals encompassing 5 orders, 9 families and 11 genera. Large mammals are represented by
excellent material of an Astrapotheriinae ungulate, tentatively assigned to Astrapotherium cf. A.
magnum. An almost complete right maxilla bearing P3 – M3, both upper canines, and isolated
lower canines and premolars is now the best preserved material of the Order Astrapotheria
known from Chile. “Nesodontinae” toxodontids are fairly abundant, including numerous
isolated teeth, mandibular and maxillary remains, and some postcranial elements of Nesodon
imbricatus and Adinotherium sp. Small ungulates of the Suborder Typotheria are represented by
various mandibular fragments and part of a skull of a hegetotheriid, most probably
Hegetotherium sp. Interatheriid remains are common and include maxillary and mandibular
fragments of both Protypotherium cf. P. australe and the smaller Interatherium cf. I. robustum.
Glyptodontids are also abundant in the Pampa Guadal fauna, and portions of carapaces have
been collected. Although this material does not easily permit a direct infra-generic taxonomic
assignment, the pattern of ornamentation exposed on the external surface of the dorsal
osteoderms shows a close resemblance to that observed in the genera Propalaehoplophorus and
Cochlops. A fragmentary mandible with three molariforms may pertain to an unspecified
megalonychid ground sloth. Identified rodents include: 1) a partial dentary with two molars of
an acaremyid octodontoid, tentatively referred to cf. Sciamys sp.; 2) isolated teeth of an
undetermined advanced eocardiid; and 3) a well preserved partial mandible of the dasyproctid
Neoreomys australis.
DISCUSSION AND CONCLUSION
The diversity of the Miocene fauna collected by our field team in Pampa Guadal perfectly
matches that of previous reports of fossil mammals in the area (De la Cruz and Suárez, 2006).
Shared occurrences include basal glyptodonts, dasyproctid rodents, astrapotheriids, toxodontids,
and interatheriids. While scant, our preliminary taxonomic identifications of the specimens
support a typical Santacrucian age (late Burdigalian, ~16.5 – 16.0 Ma) for the Pampa Guadal
deposits. A Santacrucian age was also claimed by Flynn et al. (2002) for the fossil vertebrates
recovered from Pampa Castillo, although new observations on the taxonomic status of the
rodents made by Chick et al. (2010) highlight resemblances with an older interval, the
“Pinturan” sub-age. “Pinturan” faunas are almost totally restricted to the lower and middle
sequences of the Pinturas Formation in the upper headwaters of the Pinturas River, 150 km
southeast of Meseta Cosmelli. These faunas are characterized by the presence of many lineages
apparently ancestral to those of the classic Santacrucian localities in the Atlantic coast of
Argentina. Direct 40Ar/39Ar dating of the rocks of the Pinturas and Sarmiento formations
constrain this sub-age to 17.75 to ~16.5 Ma and < 18.75 Ma, respectively (Kramarz et al., 2010).
Based on our present knowledge of the fauna, a “Pinturan” age for the Pampa Guadal fossils
cannot be securely dismissed. Certainly, more collections are needed to investigate this
intriguing possibility. The delicate but excellently preserved fossil material from Pampa Guadal
equals or exceeds that reported for Pampa Castillo, making the Meseta Cosmelli one of the
finest localities in Chile for the study of Early Miocene mammals. Our ongoing investigations in
the Lake General Carrera area, in conjunction with current research in the Alto Río Cisnes and
the Sierra Baguales regions (Bostelmann et al., this symposium), represents the first integrated
national-scale paleontological program aimed to achieve a holistic understanding of past
biological diversity and evolution of Neogene continental ecosystems in Chilean Patagonia.
ACKNOWLEDGMENTS
Successful expeditions were carried out through the diligence of our expert field team in Puerto
Guadal, led by Pascual Díaz. Francisco Mena, Mauricio Osorio (CIEP), and Peter Hartmann
were of invaluable assistance during our stay in Coyhaique. J. Le Roux, A. Kramarz, L.
González and D. Croft reviewed a first draft of this abstract. We express our deepest gratitude to
all of them.
REFERENCES
Ameghino, F., 1906. Les formations sédimentaires du Crétacé Supérieur et du Tertiaire de Patagonie avec un parallelé entre
leurs faunes mammalogiques et celles de l´ancien continent. Anales del Museo Nacional de Buenos Aires (tercera serie) 8: 1-
568.
Chick, J., Croft, D., Dodson, H., Flynn, J. & Wyss, A. 2010. The early Miocene rodent fauna of Pampa Castillo, Chile. Journal of
Vertebrate Paleontology, SVP Program and Abstracts Book 2010:71A.
De la Cruz, R. & Suárez, M. 2006. Geología del área Puerto Guadal-Puerto Sánchez, Región Aisén del General Carlos Ibañez
del Campo. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, Serie Geológica Básica No. 95, 58 p., 1 mapa
escala 1:100.000. Santiago.
Flynn, J., Novacek, M., Dodson, H., Frassinetti, D., McKenna, M., Norell, M., Sears, K., Swisher, C. & Wyss, A. 2002. A new fossil
mammal assemblage from the southern Chilean Andes: implications for geology, geochronology and tectonics. Journal of South
American Earth Sciences, 15: 285-302.
Kramarz, A., Vucetich, M.G., Carlini, A.A., Ciancio, M.R., Abello, M.A., Deschamps, M.C. & Gelfo, J.N., 2010. A new mammal
fauna at the top of the Gran Barranca sequence and its biochronological significance. In Madden, R.H., Carlini, A.A., Vucetich,
M.G. & Kay, R.F. (editors). The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle
Cenozoic of Patagonia, Cambridge University Press, Cambridge, pp. 260-273.
Marshall, L.G., Hoffstetter, R. & Pascual, R. 1983. Mammals and Stratigraphy: Geochronology of the continental mammal-
bearing tertiary of South America. Palaeovertebrata: 1-93.
Niemeyer, H. 1975. Geología de la región comprendida entre el lago General Carrera y el río Chacabuco. Provincia de Aisén,
Chile. Tesis (Memoria de Título). Departamento de Geología, Universidad de Chile, Santiago, 309 pp.
Scalabrino, B., Lagabrielle, Y., Rupelle, A., Malavieille, J., Polvé, M., Espinoza, F., Morata, D. & Suárez, M. 2009. Subduction of
an Active Spreading Ridge Beneath Southern South America: A Review of the Cenozoic Geological Records from the Andean
Foreland, Central Patagonia (46–47°S). Frontiers in Earth Sciences, 2009, Part V, 227-246.
41
exposed fossil materials. The 2012 campaign focused on expanding these observations and
continuing the rescue of the abundant skeletal elements. All specimens were found on the top of
the mesa, where they were partially or completely exposed at the surface, so that their
stratigraphic position was recorded whenever possible. The materials were transported to the
National Monuments Council and then to the vertebrate paleontology collection of the National
Museum of Natural History in Santiago. Detailed geological information of the area was
obtained from Chilean Geological Chart N°95 at a scale of 1:100.000 (De la Cruz and Suárez,
2006).
RESULTS
The fossil vertebrates collected include a small but interesting assemblage of well-preserved
mammals encompassing 5 orders, 9 families and 11 genera. Large mammals are represented by
excellent material of an Astrapotheriinae ungulate, tentatively assigned to Astrapotherium cf. A.
magnum. An almost complete right maxilla bearing P3 – M3, both upper canines, and isolated
lower canines and premolars is now the best preserved material of the Order Astrapotheria
known from Chile. “Nesodontinae” toxodontids are fairly abundant, including numerous
isolated teeth, mandibular and maxillary remains, and some postcranial elements of Nesodon
imbricatus and Adinotherium sp. Small ungulates of the Suborder Typotheria are represented by
various mandibular fragments and part of a skull of a hegetotheriid, most probably
Hegetotherium sp. Interatheriid remains are common and include maxillary and mandibular
fragments of both Protypotherium cf. P. australe and the smaller Interatherium cf. I. robustum.
Glyptodontids are also abundant in the Pampa Guadal fauna, and portions of carapaces have
been collected. Although this material does not easily permit a direct infra-generic taxonomic
assignment, the pattern of ornamentation exposed on the external surface of the dorsal
osteoderms shows a close resemblance to that observed in the genera Propalaehoplophorus and
Cochlops. A fragmentary mandible with three molariforms may pertain to an unspecified
megalonychid ground sloth. Identified rodents include: 1) a partial dentary with two molars of
an acaremyid octodontoid, tentatively referred to cf. Sciamys sp.; 2) isolated teeth of an
undetermined advanced eocardiid; and 3) a well preserved partial mandible of the dasyproctid
Neoreomys australis.
DISCUSSION AND CONCLUSION
The diversity of the Miocene fauna collected by our field team in Pampa Guadal perfectly
matches that of previous reports of fossil mammals in the area (De la Cruz and Suárez, 2006).
Shared occurrences include basal glyptodonts, dasyproctid rodents, astrapotheriids, toxodontids,
and interatheriids. While scant, our preliminary taxonomic identifications of the specimens
support a typical Santacrucian age (late Burdigalian, ~16.5 – 16.0 Ma) for the Pampa Guadal
deposits. A Santacrucian age was also claimed by Flynn et al. (2002) for the fossil vertebrates
recovered from Pampa Castillo, although new observations on the taxonomic status of the
rodents made by Chick et al. (2010) highlight resemblances with an older interval, the
“Pinturan” sub-age. “Pinturan” faunas are almost totally restricted to the lower and middle
sequences of the Pinturas Formation in the upper headwaters of the Pinturas River, 150 km
southeast of Meseta Cosmelli. These faunas are characterized by the presence of many lineages
apparently ancestral to those of the classic Santacrucian localities in the Atlantic coast of
Argentina. Direct 40Ar/39Ar dating of the rocks of the Pinturas and Sarmiento formations
constrain this sub-age to 17.75 to ~16.5 Ma and < 18.75 Ma, respectively (Kramarz et al., 2010).
Based on our present knowledge of the fauna, a “Pinturan” age for the Pampa Guadal fossils
cannot be securely dismissed. Certainly, more collections are needed to investigate this
intriguing possibility. The delicate but excellently preserved fossil material from Pampa Guadal
equals or exceeds that reported for Pampa Castillo, making the Meseta Cosmelli one of the
finest localities in Chile for the study of Early Miocene mammals. Our ongoing investigations in
the Lake General Carrera area, in conjunction with current research in the Alto Río Cisnes and
the Sierra Baguales regions (Bostelmann et al., this symposium), represents the first integrated
national-scale paleontological program aimed to achieve a holistic understanding of past
biological diversity and evolution of Neogene continental ecosystems in Chilean Patagonia.
ACKNOWLEDGMENTS
Successful expeditions were carried out through the diligence of our expert field team in Puerto
Guadal, led by Pascual Díaz. Francisco Mena, Mauricio Osorio (CIEP), and Peter Hartmann
were of invaluable assistance during our stay in Coyhaique. J. Le Roux, A. Kramarz, L.
González and D. Croft reviewed a first draft of this abstract. We express our deepest gratitude to
all of them.
REFERENCES
Ameghino, F., 1906. Les formations sédimentaires du Crétacé Supérieur et du Tertiaire de Patagonie avec un parallelé entre
leurs faunes mammalogiques et celles de l´ancien continent. Anales del Museo Nacional de Buenos Aires (tercera serie) 8: 1-
568.
Chick, J., Croft, D., Dodson, H., Flynn, J. & Wyss, A. 2010. The early Miocene rodent fauna of Pampa Castillo, Chile. Journal of
Vertebrate Paleontology, SVP Program and Abstracts Book 2010:71A.
De la Cruz, R. & Suárez, M. 2006. Geología del área Puerto Guadal-Puerto Sánchez, Región Aisén del General Carlos Ibañez
del Campo. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, Serie Geológica Básica No. 95, 58 p., 1 mapa
escala 1:100.000. Santiago.
Flynn, J., Novacek, M., Dodson, H., Frassinetti, D., McKenna, M., Norell, M., Sears, K., Swisher, C. & Wyss, A. 2002. A new fossil
mammal assemblage from the southern Chilean Andes: implications for geology, geochronology and tectonics. Journal of South
American Earth Sciences, 15: 285-302.
Kramarz, A., Vucetich, M.G., Carlini, A.A., Ciancio, M.R., Abello, M.A., Deschamps, M.C. & Gelfo, J.N., 2010. A new mammal
fauna at the top of the Gran Barranca sequence and its biochronological significance. In Madden, R.H., Carlini, A.A., Vucetich,
M.G. & Kay, R.F. (editors). The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle
Cenozoic of Patagonia, Cambridge University Press, Cambridge, pp. 260-273.
Marshall, L.G., Hoffstetter, R. & Pascual, R. 1983. Mammals and Stratigraphy: Geochronology of the continental mammal-
bearing tertiary of South America. Palaeovertebrata: 1-93.
Niemeyer, H. 1975. Geología de la región comprendida entre el lago General Carrera y el río Chacabuco. Provincia de Aisén,
Chile. Tesis (Memoria de Título). Departamento de Geología, Universidad de Chile, Santiago, 309 pp.
Scalabrino, B., Lagabrielle, Y., Rupelle, A., Malavieille, J., Polvé, M., Espinoza, F., Morata, D. & Suárez, M. 2009. Subduction of
an Active Spreading Ridge Beneath Southern South America: A Review of the Cenozoic Geological Records from the Andean
Foreland, Central Patagonia (46–47°S). Frontiers in Earth Sciences, 2009, Part V, 227-246.
