ARTÍCULOS ORIGINALES
Early Eocene 40Ar/39Ar age for the Pampa de Jones plant, frog, and insect biota (Huitrera Formation, Neuquén Province, Patagonia, Argentina)
Peter Wilf1, Brad S. Singer2, María del Carmen Zamaloa3, Kirk R. Johnson4 and N. Rubén Cúneo5
1Department of Geosciences, Pennsylvania State University,
University Park, Pennsylvania 16802, USA. pwilf@psu.edu
2Department of Geoscience, University of Wisconsin, Madison,
Wisconsin 53706, USA. bsinger@geology.wisc.edu
3Facultad de Ciencias Exactas y Naturales, Universidad de
Buenos Aires, Intendente Güiraldes 2620, 1428 Buenos Aires,
Argentina. mzamaloa@ege.fcen.uba.ar
4Department of Earth Sciences, Denver Museum of Nature& Science, Denver, Colorado 80205, USA. KJohnson@dmns.org
5Museo Paleontológico Egidio Feruglio, CONICET, 9100 Trelew,
Chubut, Argentina. rcuneo@mef.org.ar
Abstract. The Pampa de Jones fossil site, a stratigraphically isolated roadcut near the northeastern shore of Nahuel Huapi Lake in Neuquén Province, Argentina, holds a rich fossil biota including a macroflora, a microflora, insects, and most famously, an ontogenetic series of pipid frogs. The site exposes tuffaceous mudstone and sandstone beds of probable lacustrine origin, considered to belong to the volcanic Huitrera Formation. However, there have been no reliable age constraints for the fossil assemblage. We undertook laser fusion analyses of sanidine and biotite crystals occurring in a tuff layer found 4.4 m above the main fossil horizon. Twentyeight sanidine crystals yielded an 40Ar/39Ar age of 54.24 ± 0.45 Ma that is preferred over our biotite age of 53.64 ± 0.35 Ma. Pampa de Jones is thus the oldest well-dated Eocene fossil site in Patagonia, predating two other recently 40Ar/39Ar-dated sites: Laguna del Hunco (51.91 ± 0.22 Ma) and Río Pichileufú (47.46 ± 0.05 Ma). The improved age control makes possible a finer scale of evolutionary hypothesis testing and turnover analysis in the region. The age is concordant with the site's placement in the Huitrera Formation and a depositional origin related to Early Paleogene arc volcanism, and it correlates to an interval of significant climate fluctuations following the Paleocene-Eocene boundary.
Resumen. Edad 40Ar/39Ar para la biota de plantas, anuros e insectos del Eoceno temprano de Pampa de Jones (Formación Huitrera, Provincia del Neuquén, argentina). La localidad de Pampa de Jones es un afloramiento estratigráficamente aislado, cercano a la costa noreste del Lago Nahuel Huapi en la Provincia del Neuquén, Argentina. Contiene una rica biota fósil que incluye macroflora, microflora, insectos y una reconocida serie ontogenética de pípidos. La secuencia estratigráfica consiste de fangolitas y areniscas tufáceas de probable origen lacustre, asignada a la Formación Huitrera. La ausencia de datos geocronológicos directos ha impedido la estimación de edades confiables para esta paleobiota. En este trabajo se analizan por fusión láser los cristales de sanidina y biotita presentes en un nivel de toba ubicado a 4.4 m por encima del principal horizonte fosilífero. Veintiocho cristales de sanidina arrojaron una edad 40Ar/39Ar de 54.24 ± 0.45 Ma, la cual se prefiere a la edad de 53.64 ± 0.35 Ma estimada a partir de la biotita. La biota de Pampa de Jones es la más antigua del Eoceno de Patagonia datada radiométricamente, y precede a las dos localidades Eocenas datadas en la región: Laguna del Hunco (51.91 ± 0.22 Ma) y Río Pichileufú (47.46 ± 0.05 Ma). El control cronológico ajustado permitirá evaluar hipótesis evolutivas y analizar recambios en la región con una mayor resolución temporal. La edad obtenida concuerda con la ubicación de la secuencia dentro de la Formación Huitrera y con el origen de los depósitos asociados al volcanismo de arco del Paleógeno temprano, y se correlaciona con un lapso de significativas fluctuaciones climáticas ocurridas con posterioridad al pasaje Paleoceno-Eoceno.
Key words. Early Eocene; Huitrera Formation; Geochronology; Paleobotany; Patagonia; Neuquén; Argentina.
Palabras clave. Eoceno temprano; Formación Huitrera; Geocronología; Paleobotánica; Patagonia; Neuquén; Argentina.
Introduction
A significantly improved geochronologic framework
for classic Eocene fossil deposits in Argentine
Patagonia is emerging from paleomagnetic stratigraphy
and analytically precise 40Ar/39Ar radioisotopic
dating (Kay et al., 1999; Wilf et al., 2003, 2005a; Gosses,
2006). The improved age control provides the necessary
precision for diverse topics to be investigated, including
clade dating, biogeographic patterns, and
comparisons of climate change and biodiversity with
disparate regions of South America and other continents
(Petrulevicius and Nel, 2005; Wilf et al., 2005b,
2009; Zamaloa et al., 2006; Barreda and Palazzesi, 2007;
Cione and Báez, 2007; Crisp et al., 2009; Petrulevicius,
2009; Sarzetti et al., 2009; Tejedor et al., 2009).
The Pampa de Jones fossil locality of Neuquén
Province, Patagonia, Argentina (also in the literature
as "Nahuel Huapi" and "Nahuel Huapi Este"), contains
an informative biota but is not reliably dated,
limiting its usefulness in a broader evolutionary and
stratigraphic framework. The site is an accessible but
stratigraphically isolated roadcut outcrop of the Huitrera Formation within Nahuel Huapi National
Park, exposed on both the north and south sides of
Route 231 near the northeastern shore of Nahuel
Huapi Lake, close to San Carlos de Bariloche (figures
1, 2). The local strata consist of tuff and mudstone,
siltstone, and sandstone beds, somewhat more than 8
m thick on a single section line in the center of the
outcrop (appendix 1), representing a volcanic lacustrine
environment probably located near a lake margin
(see also Aragón and Romero, 1984; Báez and Pugener,
2003; Melendi et al., 2003). Most of the macrofossils
at the site occur in a blocky, silty mudstone
unit of 1 m thickness (appendix 1: Unit 16).
Figure 1. Location of the Pampa de Jones site (flag, "P. Jones") based
from Google Earth (www.earth.google.com), using tilted three-
dimensional view and 2x vertical exaggeration. Lake Nahuel
Huapi and the Limay River together define the boundary between
Río Negro (to south) and Neuquén (to north) provinces.
Varying image contrast and a near-vertical line across the image
are due to adjacent satellite coverage panels. Geographic coordinates
for the site at our line of section are S41° 02' 20.0", W71° 12' 4.1" (WGS84 datum; appendix 1) / ubicación geográfica de Pampa de
Jones (bandera, "P. Jones") basada en Google Earth (www.earth.google.
com), usando vista tridimensional inclinada y exageración vertical de
2x. El Lago Nahuel Huapi y el Río Limay determinan el límite entre las
provincias de Río Negro (al sur) y del Neuquén (al norte). Variaciones
en el contraste de la imagen y una línea casi vertical atravesando la imagen
se deben a coberturas satelitales adyacentes. Las coordenadas geográficas
del sitio en nuestra línea de sección son S41° 02' 20.0", W71° 12' 4.1" (WGS84 datum; Apéndice 1).
Figure 2. View of south (north-facing) side of the Pampa de Jones outcrop. Line of section (appendix 1) is being measured by the three workers
at bottom. Principal fossil horizon is being excavated by the two workers above. The Pampa de Jones tuff is present at the top of the exposure
and was sampled slightly to the east, where it was more freshly exposed at road level. Note dip to east, of 10° / vista de la ladera sur
(de cara al norte) del afloramiento de Pampa de Jones. La sección (Apéndice 1) está siendo medida por los tres investigadores al pie. Hacia arriba, el principal
horizonte fosilífero está siendo excavado por otros 2 investigadores. La toba de Pampa de Jones se encuentra en el tope de la exposición y fue muestreada
ligeramente hacia el este, donde presenta exposición más fresca a nivel de la ruta. Notar buzamiento hacia el este, de 10°.
The best-known fossils from Pampa de Jones are a
nearly complete ontogenetic sequence for the pipid
frog Llankibatrachus truebae (Báez, 1996; Báez and Pugener,
2003) that is an important component of the
rapidly emerging fossil history of Pipidae in Patagonia
(Casamiquela, 1961; Báez and Trueb, 1997; Cione and
Báez, 2007) and elsewhere (e.g., Rocek and Van Dijk,
2006; Rage and Dutheil, 2008). A palynoflora has also
been described (Melendi et al., 2003). Insects and plant
macrofossils from the site are frequently mentioned in
the literature (e.g., Aragón and Romero, 1984) but have
never been described or illustrated.
The outcrop lies within the mapped extent of
Paleocene-Eocene volcanic arc rocks of the Pilcaniyeu
Belt (equivalent to the Huitrera Formation of several
authors), but its location is also near an Oligocene volcanic
arc that generally crops out west of the Pilcaniyeu
belt, known as the El Maitén belt (Rapela et al., 1988).
Cazau et al. (2005) most recently summarized the history
of the highly inconsistent stratigraphic concepts
used in this area (Feruglio, 1927; 1949; Rabassa, 1978;
Ravazzoli and Sesana, 1977; González Bonorino and
González Bonorino, 1978; González Bonorino, 1979;
González Díaz, 1979; Rapela et al., 1984, 1988; Cazau et
al., 1989; Mancini and Serna, 1989; Ardolino et al., 2000).
The entire framework would benefit from substantial
revision incorporating new geochronologic data.
Within this setting, the age of the Pampa de Jones
biota has remained unknown (Aragón and Romero,
1984; Báez and Pugener, 2003). The only relevant geochronologic
data have been whole-rock K/Ar ages
from locations with very uncertain correlations to the
outcrop (González Díaz, 1979; Rapela et al., 1983, 1984;
Cazau et al., 1989; Mazzoni et al., 1991). Recently,
Melendi et al. (2003) suggested an early Eocene age by
correlating the palynological content of the outcrop. In
particular, Melendi et al. relied on a stated early
Eocene overlap of the known range endpoints of Periporopollenites
demarcatus (Chenopodiaceae, Amaranthaceae,
or Trimeniaceae) and Plicatopollis wodehousei (cf. Juglandaceae); the presence of triatriate pollen, including
P. wodehousei, linked to Juglandaceae, Myricaeae,
and Casuarinaceae, that Frederiksen and Christopher
(1978) found to decline markedly in middle Eocene
to Oligocene assemblages from the southeastern
USA; and the absence of Nothofagidites (pollen of Nothofagus).
Nothofagus is widely considered to be absent
in central and northern Patagonia during the warm
early Eocene and to become abundant by the middle
Eocene with climatic cooling (e.g., Troncoso and Romero,
1998; Melendi et al., 2003; Okuda et al., 2006; Volkheimer
and Narváez, 2006; Barreda and Palazzesi,
2007; Palazzesi and Barreda, 2007).
Although the early Eocene age for the Pampa de
Jones biota that Melendi et al. (2003) proposed from
palynological data is here confirmed, these data were
not age diagnostic. P. demarcatus is only known in
Argentina from imprecisely dated, probably middle
Eocene rocks from Río Turbio, ~1200 km to the south
of Pampa de Jones (Romero and Zamaloa, 1985; Malumián
and Caramés, 1997), and otherwise from
Australia, where it ranges from the early Eocene to
the early Miocene in the Gippsland Basin (Stover and
Partridge, 1973: p. 273). P. wodehousei is known in Argentina
only from the early Paleocene Salamanca
Formation at a site in Santa Cruz ~770 km south of
Pampa de Jones (Zamaloa and Andreis, 1995), and
Frederiksen and Christopher's (1978) data regarding Plicatopollis came from a single core in South Carolina
that did not contain P. wodehousei. The absence of Nothofagus from the early Eocene of Patagonia was described
from a handful of floras, and none of these
was reliably constrained to the early Eocene.
Interestingly, the nearby Confluencia locality (37
km to the north-northeast; Pascual and Odreman
Rivas, 1973; Aragón and Romero, 1984), which has
produced the only other occurrence of the pipid Llankibatrachus truebae (Báez et al., 1990; Báez and Pugener,
2003), has a great abundance of Nothofagus pollen (Báez et al., 1990; Melendi et al., 2003). The only
age control for Confluencia is very tentative,
namely a whole-rock K-Ar date of 52 ± 3 Ma from a
sampling location with uncertain relationship to the
fossils (Rapela et al., 1983, 1984).
We visited Pampa de Jones, sampled the thick tuff
layer at the top of the exposure for 40Ar/39Ar analyses,
and made preliminary fossil collections. Here, we report
the results, discuss their regional and global implications,
and provide a preliminary look at the macroflora.
Materials and methods
Our field work took place on 21 March, 2004 and 7 March, 2005. A single line of section was measured at the thickest exposure on the south (north-facing) side of the Pampa de Jones roadcut, where macrofossils are most accessible (figure 2; appendix 1). In order to refine stratigraphic understanding of the pollen content of the outcrop, pollen samples were collected from several horizons and processed using standard techniques; six horizons yielded palynomorphs as indicated in appendix 1. Approximately 100 plant macrofossils were collected using standard bench quarrying techniques, mostly consisting of angiosperm leaves but including some fruits and seeds as well as conifer material. These are under separate study, but because no plant macrofossils have been illustrated from Pampa de Jones since their existence was first mentioned in the literature (Aragón and Romero, 1984), we provide a sample here (figure 3), including some others from the site housed in the collections of the University of Buenos Aires (FCENCB-PB acronym). The number of species and preservational quality of specimens is not yet sufficient for paleoclimate analysis from leaf morphology (e.g., Greenwood, 2007). The collection also includes several tadpoles of Llankibatrachus truebae and unidentified insects awaiting study. Specimens from the 2004 field trip are temporarily deposited at Administración de Parques Nacionales, Delegación Regional Patagonia, San Carlos de Bariloche (APN), awaiting a permanent repository assignment, and those from 2005 are deposited at the Museo Paleontológico Egidio Feruglio, Trelew (MPEF-Pb). The tuff sample was collected from the uppermost horizon in the measured section (appendix 1), after tracing down to road level along the 10°E dip for better access.
Figure 3. Preliminary sample of plant macrofossils from Pampa de Jones. Affinities unknown except where indicated. Additional descriptive
details given in Appendix 3. Scale bars = 5 mm for B-E, 1 cm for others. Scale for (P) unavailable, but its size is similar to (O).
If equivalent or similar to forms known from Laguna del Hunco (LH) or Río Pichileufú (RP), so indicated (Berry, 1938; Wilf et al., 2005a).
/ muestra preliminar de los macrofósiles vegetales de Pampa de Jones. Afinidades desconocidas, excepto cuando son indicadas. Detalles descriptivos
adicionales se dan en Apéndice 3. Escala gráfica = 5 mm para B-E, 1 cm para el resto. Escala no disponible para (P), pero su tamaño es similar a (O).
Si existen formas equivalentes o similares a las conocidas para Laguna del Hunco o Río Pichileufú, se indican (Berry, 1938; Wilf et al., 2005a). A,
Podocarpaceae, foliage / Podocarpaceae, follaje, (LH, RP), APN. B, Araucaria cf. A. pichileufensis Berry, cone scale with seed / Araucaria
cf. A. pichileufensis Berry, escama con semilla, (LH, RP), FCENCB-PB 270. C, angiosperm reproductive structure / estructura reproductiva
de angiosperma, MPEF-Pb 3630. D, angiosperm flower / flor de angiosperma, FCENCB-PB 271. E, angiosperm seed / semilla de angiosperma,
FCENCB-PB 272A. F-G, probable Cunoniaceae leaflets / probables folíolos de Cunoniaceae, (LH, RP), MPEF-Pb 3631 (F), APN (G). H, ovate,
toothed angiosperm leaf morphotype / morfotipo foliar de angiosperma, ovado con márgen dentado, MPEF-Pb 3632. I, probable Fabaceae
leaflet / probable folíolo de Fabaceae, MPEF-Pb 3633. J, elliptic angiosperm leaf morphotype / morfotipo foliar elíptico de angiosperma,
FCENCB-PB 269A. K-N, angiosperm leaf morphotypes / morfotipos foliares de angiosperma, MPEF-Pb 3634 (K), MPEF-Pb 3635 (L), MPEFPb
3636 (M, ?Salicaceae), and MPEF-Pb 3637 (N). O, probable Malvaceae s.l. leaf morphotype / morfotipo foliar de probable Malvaceae s.l.,
MPEF-Pb 3638. P, second probable Malvaceae s.l. morphotype / segundo morfotipo foliar de probable Malvaceae s.l., APN. Q, angiosperm
leaf morphotype similar to a form occurring at LH (morphotype TY057 of Wilf et al., 2005) / morfotipo foliar de angiosperma similar a uno
registrado en LH (morfotipo TY057 de Wilf et al., 2005), FCENCB-PB 274A.
In the University of Wisconsin-Madison Rare Gas Geochronology Laboratory, sanidine and biotite separated from the tuff were cleaned, irradiated, and analyzed as single crystals, using a CO2 laser to fuse the crystals and a fully automated gas-handling and mass-spectrometry system to measure the isotopic composition. Sample preparation, analytical methods and procedures for calculating 40Ar/39Ar ages are fully documented in Smith et al. (2008a). Uncertainties in age are reported at the 95% level of confidence (±2s).
Results
A total of 35 sanidine and 34 biotite crystals were fused and analyzed; apparent ages range from ca. 51 to 740 Ma for the sanidine and 52 to 617 Ma for the biotite (appendix 2). However, the youngest 28 sanidine and 17 biotite crystals yielded Gaussian probability distributions, strongly suggesting that crystals yielding older apparent ages are xenocrysts (figure 4). Excluding these older crystals, the inverse-variance weighted mean age of the 28 sanidine crystals is 54.24 ± 0.45 Ma; these define an inverse isochron age of 54.41 ± 0.98 Ma, with an atmospheric 40Ar/36Ar intercept value of 306 ± 11. Likewise, 17 of the biotite crystals yielded an inverse-variance weighted mean age of 54.64 ± 0.35 Ma and an inverse isochron age of 54.18 ± 0.81 Ma, with an 40Ar/36Ar intercept value of 292 ± 5 (figure 4; table 1). The four ages are indistinguishable from one another, consistent with an eruption age of ca. 54 Ma. Because there is no evidence from the isochrons that excess argon is present in levels large enough to bias the age, and because biotite can be problematic owing to subtle alteration effects (Smith et al., 2006, 2008b), we take the weighted mean age of 54.24 ± 0.45 Ma of the sanidine as the best estimate of time elapsed since deposition of the Pampa de Jones tuff.
Figure 4. Apparent ages (A, B) and isochrons (C, D) calculated from the youngest sub-populations of measured sanidine (A, C) and biotite (B,
D) crystals. Many older crystals (open symbols) plot off the diagrams and are not included in the weighted mean age or isochron calculations.
The weighted mean of 28 sanidine crystals, 54.24 ± 0.45 Ma (A), is the preferred age of the Pampa de Jones tuff. All ages calculated relative to
28.34 Ma Taylor Creek rhyolite sanidine (equivalent to 28.02 Ma Fish Canyon Tuff sanidine). Uncertainties are ±2s / edades aparentes (A, B) e
isócronas (C, D) calculadas a partir de las sub-poblaciones más jóvenes de cristales medidos de sanidina (A, C) y biotita (B, D). Muchos cristales más antiguos
(símbolos abiertos) caen fuera de los diagramas y no fueron incluidos en la edad media ponderada ni en cálculos isocrónicos. La media ponderada de 28 cristales
de sanidina, 54.24 ± 0.45 Ma (A), es la edad preferida para la toba de Pampa de Jones. Todas las edades fueron calculadas en relación a la sanidina de la riolita
de Taylor Creek de 28.34 Ma (que es equivalente a la sanidina de la toba de Fish Canyon de 28.02 Ma). Las incertidumbres son de ±2s.
Table 1. Summary of 40Ar/39Ar laser-fusion experimental results, Pampa de Jones tuff / resumen de los resultados experimentales de fusión
por láser 40Ar/39Ar, toba de Pampa de Jones.
The pollen samples yielded a composition that
was, as expected, quite similar to that reported by
Melendi et al. (2003) and was not studied in detail: a
mixture of fungal spores and fruiting bodies, monolete
and trilete spores from bryophytes and pteridophytes,
bisaccate and trisaccate pollen of Podocarpaceae,
and porate angiosperm pollen. There
were no significant differences in palynological composition
between sampling levels (appendix 1).
The macroflora so far studied (figure 3 and caption)
shows some similarity to the ~2.3 m.y. younger
Laguna del Hunco assemblages, though quantifying
the overlap requires more data; the Laguna del Hunco
floras are sampled approximately 60 times more heavily
than Pampa de Jones (Wilf et al., 2005a). However,
the four most common leaf taxa at Laguna del Hunco
are so far absent at Pampa de Jones, "Celtis" ameghenoi,
"Myrcia" chubutensis, "Tetracera" patagonica, and
"Schmidelia" proedulis (Wilf et al., 2005a). In accord
with the Pampa de Jones palynoflora, Podocarpaceae
and Araucaria are present (figure 3.A, B), and there are
no macrofossils comparable to Nothofagus.
Discussion
Our 40Ar/40Ar results place the formerly isolated
Pampa de Jones site into a much broader framework,
laying out several productive avenues for future research.
The Pampa de Jones biota can now be compared
in a reliable temporal context to other regional
assemblages, particularly Laguna del Hunco and Río
Pichileufú, to refine hypotheses about evolutionary
dates, biotic turnover, and landscape and climate
change. The age is consistent with deposition during
the Pilcaniyeu stage of volcanism (Rapela et al., 1984);
it provides a new, well-resolved constraint for interpreting
regional magmatic history, though many
more new ages are needed.
The Pampa de Jones assemblage is now the oldest
Eocene macrofossil biota known in Patagonia (and
probably in South America), providing a unique window
into Patagonian ecosystems shortly after the
Paleocene-Eocene boundary (55.8 Ma). Further investigation
for paleoclimatic proxy data is merited to
broaden understanding of significant climate fluctuations
observed elsewhere near 54 Ma (Bao et al.,
1999; Wing et al., 2000; Secord et al., 2008; Zachos et al., 2008; Chew, 2009). Pampa de Jones is now the only
demonstrably early Eocene site in the region examined
for Nothofagus pollen, supporting the idea
that the genus was absent at this time (e.g., Troncoso
and Romero, 1998; Melendi et al., 2003; Barreda and
Palazzesi, 2007; Palazzesi and Barreda, 2007).
However, we caution strongly against a broad regional
and temporal interpretation using absence data
from a single well-dated site. The nearby Confluencia
locality has also produced the pipid
Llankibatrachus truebae, but it has a different palynoflora
from Pampa de Jones, including abundant
Nothofagus pollen of both brassii and fusca types (Báez et al., 1990; Melendi et al., 2003). Accordingly, the
Confluencia assemblages are considered middle
Eocene or younger (Melendi et al., 2003). Although a
middle Eocene age is certainly possible, radioisotopic
dating of the Confluencia deposits is needed to determine
whether Confluencia is instead close in age
to Pampa de Jones, which would indicate that the
among-site difference in Nothofagus abundance is
due to climate or landscape changes that are relatively
closely spaced in time.
Appendix 1. Measured stratigraphic section at Pampa de Jones* / sección estratigráfica medida en Pampa de Jones*
Appendix 2. Complete 40Ar/39Ar single step single crystal fusion results, Pampa de Jones tuff / resultados completos de la fusión 40Ar/39Ar
por láser realizada en un único cristal en un solo paso, toba de Pampa de Jones.
Appendix 3. Additional description of selected fossils shown in Figure 3/ descripción adicional de los fósiles seleccionados mostrados en la figura 3.
Descriptive terminology for distinctive features from Ellis et al. (2009) / para los rasgos distintivos se aplica la terminología descriptiva de Ellis et al. (2009). F-G, equivalent to "Cupania" latifolioides Berry (1938: sensu plate 30, figure 1)/ equivalente a "Cupania" latifolioides Berry (1938: según lámina 30, figura 1). I, leaflet, asymmetrical, with untoothed margin and numerous, thin, brochidodromous secondary veins. Pulvinulus not preserved. Similar foliage is common at both Laguna del Hunco and Río Pichileufú (e.g., "Cassia" argentinensis Berry)/ folíolo, asimétrico, con margen entero y numerosas venas secundarias delgadas y broquidódromas. Pulvínulos no preservados. Follaje similar es común tanto en Laguna del Hunco como en Río Pichileufú (p.e., "Cassia" argentinensis Berry). J, numerous secondary and intersecondary veins, untoothed margin / numerosas venas secundarias e intersecundarias, margen entero. K, actinodromous primary venation, agrophic veins, opposite percurrent tertiary veins oriented perpendicular to primaries, and bluntly toothed margin/ venación primaria actinódroma, venas agróficas, venas terciarias opuestas percurrentes orientadas perpendicularmente a las primarias y margen con dientes romos. L, leaf distal portion with strong intersecondaries, well-preserved high-order venation, and large, narrow, irregular teeth with concave apical flanks and variable basal flanks / porción distal de hoja con venas intersecundarias robustas, venación de alto orden bien preservada y dientes grandes, angostos, irregulares, con lado apical cóncavo y lado basal variable. M, distal leaf portion having closely spaced, blunt, teeth with conspicuous apical glands/ porción distal de hoja con dientes poco espaciados, romos, con conspicuas glándulas apicales. N, leaf margin (remainder of leaf poorly preserved) showing distinctive teeth that are irregularly sized, large, closely spaced, and deeply incised with convex proximal flanks/ margen de hoja (reminiscente a una hoja pobremente preservada) mostrando dientes característicos grandes, de tamaño irregular, poco espaciados y profundamente incisos con lados proximales convexos. O, rounded base, three convex-sided lobes, rounded lobe sinuses, three stout, actinodromous primary veins, agrophic veins, and untoothed margin. A similar form is found at Laguna del Hunco (e.g., Wilf et al., 2003: fig. 1.J) / base redondeada, tres lóbulos de lados convexos y senos redondeados, tres venas primarias robustas, actinódromas, venas agróficas, y margen entero. Una forma similar se encuentra en Laguna del Hunco (p.e., Wilf et al., 2003: fig. 1.J). P, similar to previous but with a toothed margin, preserving orthogonal reticulate high-order venation/ similar a la anterior pero con margen dentado, venación de alto orden reticulada ortogonal preservada. Q, seven actinodromous primary veins, compound agrophic veins with conspicuously forking minor secondaries, concentric percurrent tertiary veins, and toothed margin/ siete venas primarias actinódromas, venas agróficas compuestas con secundarias menores conspicuamente bifurcadas, venas terciarias percurrentes concéntricas y margen dentado.
Acknowledgements
We thank the National Science Foundation, grants DEB-0345750 and DEB 0919071, for support of this research; A. Báez, an anonymous reviewer, and the Editor for helpful critiques; E. Aragón and A. Iglesias for critiquing earlier drafts; Parque Nacional Nahuel Huapi and C. Chehebar for site access; and R. Burnham, L. Canessa, B. Cariglino, M. Carvalho, E. Currano, C. González, P. Puerta, and E. Ruigomez for field and laboratory assistance.
References
1. Aragón, E. and Romero, E.J. 1984. Geología, paleoambientes y paleobotánica de yacimientos Terciarios del occidente de Río Negro, Neuquén y Chubut. 9º Congreso Geológico Argentino (San Carlos de Bariloche), Actas 4: 475-507.
2. Ardolino, A., M. Franchi, M. Remesal, and F. Salani. 2000. La sedimentación y el volcanismo terciarios en la Patagonia extraandina. 2. El volcanismo en la Patagonia extraandina. In: R. Caminos (ed.), Geología Argentina. Servicio Geológico Minero Argentino, Instituto de Geología y Recursos Minerales, Anales 29: 579-601.
3. Báez, A.M. 1996. The fossil record of the Pipidae. In: R.C. Tinsley and H.R. Kobel (eds.), The biology of Xenopus. Symposia of the Zoological Society of London 68. Clarendon Press, Oxford, pp. 329-347.
4. Báez, A.M. and Pugener, L.A. 2003. Ontogeny of a new Palaeogene pipid frog from southern South America and xenopodinomorph evolution. Zoological Journal of the Linnean Society 139: 439-476.
5. Báez, A.M. and Trueb, L. 1997. Redescription of the Paleogene Shelania pascuali from Patagonia and its bearing on the relationships of fossil and Recent pipoid frogs. Scientific Papers, Natural History Museum, The University of Kansas 4: 1-41.
6. Báez, A.M., Zamaloa, M.C. and Romero, E.J. 1990. Nuevos hallazgos de microfloras y anuros Paleógenos en el Noroeste de Patagonia: implicancias paleoambientales y paleobiogeográficas. Ameghiniana 27: 83-94.
7. Bao, H.M., Koch, P.L. and Rumble, D.I. 1999. Paleocene-Eocene climatic variation in western North America: evidence from the d18O of pedogenic hematite. Geological Society of America Bulletin 111: 1405-1415.
8. Barreda, V. and Palazzesi, L. 2007. Patagonian vegetation turnovers during the Paleogene-early Neogene: origin of arid-adapted floras. Botanical Review 73: 31-50.
9. Berry, E.W. 1938. Tertiary flora from the Río Pichileufú, Argentina. Geological Society of America Special Paper 12: 1-149.
10. Casamiquela, R.M. 1961. Un pipoideo fósil de Patagonia. Revista del Museo de La Plata, Sección Paleontología 4: 71-123.
11. Cazau, L., Mancini, D., Cangini, J. and Spalletti, L.A. 1989. Cuenca de Ñirihuau. In: G.A. Chebli and L.A. Spalletti (eds.), Cuencas sedimentarias Argentinas, Serie Correlación Geológica no. 6. Universidad Nacional de Tucumán, Instituto Superior de Correlación Geológica, San Miguel de Tucumán, pp. 299-318.
12. Cazau, L., Cortiñas, J., Reinante, S., Asensio, M., Bechis, F. and Apreda, D. 2005. Cuenca de Ñirihuau. In: G. Chebli, J.S. Cortiñas, L. Spalletti, L. Legarreta and E.L. Vallejo (eds.), Frontera exploratoria de la Argentina. 6º Congreso de Exploración y Desarrollo de Hidrocarburos (Mar del Plata), Actas 1: 251-273.
13. Chew, A.E. 2009. Paleoecology of the early Eocene Willwood mammal fauna from the central Bighorn Basin, Wyoming. Paleobiology 35: 13-31.
14. Cione, A.L. and Báez, A.M. 2007. Peces continentales y anfibios Cenozoicos de Argentina: los últimos cincuenta años. Asociación Paleontológica Argentina. Publicación Especial 11: 195-220.
15. Crisp, M.D., Arroyo, M.T.K., Cook, L.G., Gandolfo, M.A., Jordan, G.J., McGlone, M.S., Weston, P.H., Westoby, M., Wilf, P. and Linder, H.P. 2009. Phylogenetic biome conservatism on a global scale. Nature 458: 754-756.
16. Ellis, B., Daly, D., Hickey, L.J., Johnson, K.R., Mitchell, J., Wilf, P. and Wing, S.L. 2009. Manual of leaf architecture. Cornell University Press, Ithaca, 190 pp.
17. Feruglio, E. 1927. Estudio geológico de la región pre- y subandina en la latitud del Nahuel Huapí. Boletín de Informaciones Petroleras 4: 425-434.
18. Feruglio, E. 1949. Descripción geológica de la Patagonia, vol. II. Ministerio de Industria y Comercio de la Nación, Dirección General de Yacimientos Petrolíferos Fiscales, Buenos Aires, 349 pp.
19. Frederiksen, N.O. and Christopher, R.A. 1978. Taxonomy and biostratigraphy of Late Cretaceous and Paleogene triatriate pollen from South Carolina. Palynology 2: 113-145.
20. González Bonorino, F.G. 1979. Esquema de la evolución geológica de la Cordillera Norpatagónica. Revista de la Asociación Geológica Argentina 34: 184-202.
21. González Bonorino, F.G. and González Bonorino, G.G. 1978. Geología de la region de San Carlos de Bariloche: un estudio de las formaciones Terciarias del Grupo Nahuel Huapi. Revista de la Asociación Geológica Argentina 33: 175-210.
22. González Díaz, E.F. 1979. La edad de la Formación Ventana, en el área al norte y al este del Lago Nahuel Huapi. Revista de la Asociación Geológica Argentina 34: 113-124.
23. Gosses, J. 2006. [Stratigraphy and 40Ar/39Ar geochronology of the Laguna del Hunco Formation: a lacustrine and sub-aerial caldera moat formation. Masters Thesis, Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin, 265 pp. Unpublished.].
24. Greenwood, D.R. 2007. Fossil angiosperm leaves and climate: from Wolfe and Dilcher to Burnham and Wilf. Courier Forschungsinstitut Senckenberg 258: 95-108.
25. Kay, R.F., Madden, R.H., Vucetich, M.G., Carlini, A.A., Mazzoni, M.M., Re, G.H., Heizler, M. and Sandeman, H. 1999. Revised geochronology of the Casamayoran South American land mammal age: climatic and biotic implications. Proceedings of the National Academy of Sciences USA 96: 13235-13240.
26. Malumián, N. and Caramés, A. 1997. Upper Campanian-Paleogene from the Río Turbio coal measures in southern Argentina: micropaleontology and the Paleocene/Eocene boundary. Journal of South American Earth Sciences 10: 189-201.
27. Mancini, C.D. and Serna, M.J. 1989. Evaluación petrolera de la Cuenca de Ñirihuau, sudoeste de Argentina. 1º Congreso Nacional de Exploración de Hidrocarburos, (Mar del Plata), Actas 2: 739-762.
28. Mazzoni, M.M., Kawashita, K., Harrison, S. and Aragón, E. 1991. Edades radimétricas Eocenas. Borde occidental del Macizo Norpatagónico. Revista de la Asociación Geológica Argentina 46: 150-158.
29. Melendi, D.L., Scafati, L.H. and Volkheimer, W. 2003. Palynostratigraphy of the Paleogene Huitrera Formation in N-W Patagonia, Argentina. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 228: 205-273.
30. Okuda, M., Nishida, H., Uemura, K. and Yabe, A. 2006. Paleocene/ Eocene pollen assemblages from the Ligorio Márquez Formation, central Patagonia, XI Region, Chile. In: H. Nishida (ed.), Post-Cretaceous floristic changes in southern Patagonia, Chile. Faculty of Science and Enginneering, Chuo University, Tokyo, pp. 37-43.
31. Palazzesi, L. and Barreda, V. 2007. Major vegetation trends in the Tertiary of Patagonia (Argentina): a qualitative paleoclimatic approach based on palynological evidence. Flora 202: 328-337.
32. Pascual, R. and Odreman Rivas, O. 1973. Las unidades estratigráficas del Terciario portadoras de mamíferos. Su distribución y sus relaciones con los acontecimientos diastróficos. 5ºCongreso Geológico Argentino (Buenos Aires), Actas 3: 292-338.
33. Petrulevicius, J.F. 2009. A panorpoid (Insecta: Mecoptera) from the lower Eocene of Patagonia, Argentina. Journal of Paleontology 83: 994-997.
34. Petrulevicius, J.F. and Nel, A. 2005. Austroperilestidae, a new family of damselflies from early Eocene of Argentina (Insecta: Odonata). Phylogenetic relationships within Odonata. Journal of Paleontology 79: 658-662.
35. Rabassa, J. 1978. Estratigrafía de la región de Pilcaniyeu. Comallo, Provincia de Río Negro. 7º Congreso Geológico Argentino (Neuquén), Actas 1: 731-746.
36. Rage, J.C. and Dutheil, D.B. 2008. Amphibians and squamates from the Cretaceous (Cenomanian) of Morocco: a preliminary study, with description of a new genus of pipid frog. Palaeontographica Abteilung A 285: 1-22.
37. Rapela, C.W., Spalletti, L.A. and Merodio, J.C. 1983. Evolución magmática y geotectónica de la "Serie Andesítica" Andina (Paleoceno- Eoceno) en la Cordillera Norpatagónica. Revista de la Asociación Geológica Argentina 38: 469-484.
38. Rapela, C.W., Spalletti, L.A., Merodio, J.C. and Aragón, E. 1984. El vulcanismo Paleoceno-Eoceno de la provincia volcánica Andino- Patagónica. 9º Congreso Geológico Argentino, Relatorio 1: 189-213.
39. Rapela, C.W., Spalletti, L.A., Merodio, J.C. and Aragón, E. 1988. Temporal evolution and spatial variation of early Tertiary volcanism in the Patagonian Andes (40° S-42°30' S). Journal of South American Earth Sciences 1: 75-88.
40. Ravazzoli, I.A. and Sesana, F.L. 1977. Descripción geológica de la Hoja 41c, Río Chico, provincia de Río Negro. Servicio Geológico Nacional (Buenos Aires), Boletín 148: 1-80.
41. Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, T.L. and DePaolo, D.J. 1998. Intercalibration of standards, absolute ages and uncertainties in 40Ar/39Ar dating. Chemical Geology 145: 117-152.
42. Rocek, Z. and Van Dijk, E. 2006. Patterns of larval development in Cretaceous pipid frogs. Acta Palaeontologica Polonica 51: 111-126.
43. Romero, E.J. and Zamaloa, M.C. 1985. Polen de angiospermas de la Formación Río Turbio (Eoceno), Pcia. de Santa Cruz, Argentina. Ameghiniana 34: 207-214.
44. Sarzetti, L.C., Labandeira, C.C., Muzón, J., Wilf, P., Cúneo, N.R., Johnson, K.R. and Genise, J.F. 2009. Odonatan endophytic oviposition from the Eocene of Patagonia: the ichnogenus Paleoovoidus and implications for behavioral stasis. Journal of Paleontology 83: 431-447.
45. Secord, R., Wing, S.L. and Chew, A. 2008. Stable isotopes in early Eocene mammals as indicators of forest canopy structure and resource partitioning. Paleobiology 34: 282-300.
46. Smith, M.E., Singer, B.S., Carroll, A.R. and Fournelle, J.H. 2006. Highresolution calibration of Eocene strata: 40Ar/39Ar geochronology of biotite in the Green River Formation. Geology 34: 393-396.
47. Smith, M.E., Carroll, A.R. and Singer, B.S. 2008a. Synoptic reconstruction of a major ancient lake system: Eocene Green River Formation, western United States. Geological Society of America Bulletin 120: 54-84.
48. Smith, M.E., Singer, B.S., Carroll, A.R. and Fournelle, J.H. 2008b. Precise dating of biotite in distal volcanic ash: isolating subtle alteration using 40Ar/39Ar laser incremental heating and electron microprobe techniques. American Mineralogist 93: 784-795.
49. Steiger, R.H. and Jäger, E. 1977. Subcommission on geochronology: convention on the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters 36: 359-362.
50. Stover, L.E. and Partridge, A.D. 1973. Tertiary and Late Cretaceous spores and pollen from the Gippsland Basin, Victoria 85: 237-286.
51. Tejedor, M.F., Goin, F.J., Gelfo, J.N., López, G., Bond, M., Carlini, A.A., Scillato-Yané, G.J., Woodburne, M.O., Chornogubsky, L., Aragón, E., Reguero, M.A., Czaplewski, N.J., Vincon, S., Martin, G.M. and Ciancio, M.R. 2009. New early Eocene mammalian fauna from western Patagonia, Argentina. American Museum Novitates 3638: 1-43.
52. Troncoso, A. and Romero, E.J. 1998. Evolución de las comunidades florísticas en el extremo sur de Sudamérica durante el Cenofitico. Monographs in Systematic Botany from the Missouri Botanical Garden 68: 149-172.
53. Volkheimer, W. and Narváez, P. 2006. Nuevos hallazgos de palinofloras del Paleógeno en el Norte Patagónico (Argentina). Significado estratigráfico, paleoclimático y paleoambiental. 13º Simposio Argentino de Paleobotánica y Palinología (Bahía Blanca), Resúmenes: 82.
54. Wilf, P., Cúneo, N.R., Johnson, K.R., Hicks, J.F., Wing, S.L. and Obradovich, J.D. 2003. High plant diversity in Eocene South America: evidence from Patagonia. Science 300: 122-125.
55. Wilf, P., Johnson, K.R., Cúneo, N.R., Smith, M.E., Singer, B.S. and Gandolfo, M.A. 2005a. Eocene plant diversity at Laguna del Hunco and Río Pichileufú, Patagonia, Argentina. American Naturalist 165: 634-650.
56. Wilf, P., Labandeira, C.C., Johnson, K.R. and Cúneo, N.R. 2005b. Richness of plant-insect associations in Eocene Patagonia: a legacy for South American biodiversity. Proceedings of the National Academy of Sciences USA 102: 8944-8948.
57. Wilf, P., Little, S.A., Iglesias, A., Zamaloa, M.C., Gandolfo, M.A., Cúneo, N.R. and Johnson, K.R. 2009. Papuacedrus (Cupressaceae) in Eocene Patagonia, a new fossil link to Australasian rainforests. American Journal of Botany 96: 2031-2047.
58. Wing, S.L., Bao, H. and Koch, P.L. 2000. An early Eocene cool period? Evidence for continental cooling during the warmest part of the Cenozoic. In: B.T. Huber, K. MacLeod and S.L. Wing (eds.), Warm climates in Earth history. Cambridge University Press, Cambridge, pp. 197-237.
59. Zachos, J.C., Dickens, G.R. and Zeebe, R.E. 2008. An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics. Nature 451: 279-283.
60. Zamaloa, M.C. and Andreis, R.R. 1995. Asociación palinológica del Paleoceno temprano (Formación Salamanca) en Ea. Laguna Manantiales, Santa Cruz, Argentina. 6º Congreso Argentino de Paleontología y Bioestratigrafía (Trelew), Actas: 301-305.
61. Zamaloa, M.C., Gandolfo, M.A., González, C.C., Romero, E.J., Cúneo, N.R. and Wilf, P. 2006. Casuarinaceae from the Eocene of Patagonia, Argentina. International Journal of Plant Sciences 167: 1279-1289.
Recibido: 20 de mayo de 2009.
Aceptado: 20 de octubre de 2009.