university of zurich - uzh · ortiz jaureguizar, 1991). an important limi-tation—as noted by bond...

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New Early Eocene mammalian fauna from western Patagonia,Argentina

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; Ciancio, M R

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; Ciancio, M R (2009). NewEarly Eocene mammalian fauna from western Patagonia, Argentina. American Museum Novitates, (3638):1-43.Postprint available at:http://www.zora.uzh.ch

Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch

Originally published at:American Museum Novitates 2009, (3638):1-43.

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; Ciancio, M R (2009). NewEarly Eocene mammalian fauna from western Patagonia, Argentina. American Museum Novitates, (3638):1-43.Postprint available at:http://www.zora.uzh.ch

Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch

Originally published at:American Museum Novitates 2009, (3638):1-43.

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY

CENTRAL PARK WEST A T 79TH STREET, NEW YOR K, NY 10024

Number 3638, 43 pp., 10 figures, 1 table March 31, 2009

New Early Eocene Mammalian Fauna fromWestern Patagonia, Argentina

MARCELO F. TEJEDOR,1,2,8 FRANCISCO J. GOIN,3,8 JAVIER N. GELFO,3,8

GUILLERMO LOPEZ,3 MARIANO BOND,3,8 ALFREDO A. CARLINI,3,8,9

GUSTAVO J. SCILLATO-YANE,3,8 MICHAEL O. WOODBURNE,4 LAURA

CHORNOGUBSKY,5,8 EUGENIO ARAGON,6,8 MARCELO A. REGUERO,3,8

NICHOLAS J. CZAPLEWSKI,7 SERGIO VINCON,2 GABRIEL M. MARTIN,2,8

AND MARTIN R. CIANCIO3,8

ABSTRACT

Two new fossil mammal localities from the Paleogene of central-western Patagonia arepreliminarily described as the basis for a new possible biochronological unit for the early Eocene ofPatagonia, correlated as being between two conventional SALMAs, the Riochican (older) and theVacan subage of the Casamayoran SALMA. The mammal-bearing strata belong to the MiddleChubut River Volcanic-Pyroclastic Complex (northwestern Chubut Province, Argentina), of

Copyright E American Museum of Natural History 2009 ISSN 0003-0082

1 Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History, Central Park West at 79thStreet, New York, NY 10024, U.S.A. ([email protected]).

3 Division Paleontologıa Vertebrados, Facultad de Ciencias Naturales y Museo de La Plata, Paseo del Bosque s/n,B1900FWA La Plata, Argentina ([email protected]).

4 Department of Geology, Museum of Northern Arizona, Flagstaff, AZ 86001. Research Associate, Department ofVertebrate Paleontology, American Museum of Natural History, ([email protected]).

5 Seccion Paleontologıa de Vertebrados, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Av. AngelGallardo nu 470, 1405 Buenos Aires, Argentina ([email protected]).

6 Centro de Investigaciones Geologicas, Universidad Nacional de La Plata, Calle 1 nu 644, B1900FWA La Plata,Argentina ([email protected]).

7 University of Oklahoma, Oklahoma Museum of Natural History, 2401 Chautauqua Ave, Norman, OK 73072-7029,U.S.A. ([email protected]).

8 CONICET (Consejo Nacional de Investigaciones Cientıficas y Tecnicas, Argentina).9 Palaontologisches Institut und Museum, Universitat Zurich, Karl Schmid-Straße 4, CH-8006 Zurich, Switzerland.

2Current address: LIEB (Laboratorio de Investigaciones en Evolucion y Biodiversidad), Facultad de Ciencias Naturales,Sede Esquel, Universidad Nacional de la Patagonia ‘‘San Juan Bosco’’, Sarmiento 849, 9200 Esquel, Provincia del Chubut,Argentina.

Paleocene-Eocene age. This complex includes a variety of volcaniclastic, intrusive, pyroclastic, andextrusive rocks deposited after the K-T boundary. Geochronological data taken from nearbyvolcanic deposits that underlie and overlie the mammal-bearing levels indicate that both faunas areof late early Eocene age (Ypresian-Lutetian boundary). In addition to more than 50 species ofmammals, including marsupials, ungulates, and xenarthrans, two lower molars are the oldestevidence of bats in South America. Paleobotanical and palynological evidence from inferredcontemporary localities nearby indicate subtropical environments characterized by warm andprobably moderately humid climate. Remarkably, this new fauna is tentatively correlated withEocene mammals from the La Meseta Formation in the Antarctic Peninsula. We conclude that thetwo localities mentioned above are part of a possible new biochronological unit, but the formalproposal of a new SALMA awaits completion of taxonomic analysis of the materials reportedupon here. If the La Meseta fauna is correlated biochronologically to western Patagonia, this alsosuggests a continental extension of the biogeographic Weddelian Province as far north as central-western Patagonia.

INTRODUCTION

The past two decades have seen an increasein the number of studies on the evolutionof Paleogene South American mammals.Consequently, knowledge of their taxonomy,biostratigraphy, biogeography, and geochro-nology has been substantially improved. As anexample, the biochronological sequence forthe South American Paleogene showed norelevant changes from 1948 through themiddle 1980s (Simpson, 1948; Marshall etal., 1983; Pascual et al., 1965, Patterson andPascual, 1972). Subsequent taxonomic, geo-chronological, and biostratigraphic studieshave contributed greatly in improving ourunderstanding of the faunal evolution andsuccession of South American mammals(Flynn and Swisher, 1995, and referencestherein; Pascual et al., 1996). This has resultedin the identification of nearly 20 SouthAmerican Land Mammal Ages (SALMAs).Land Mammal Ages have been recognized asbiochronological units (Pascual et al., 1965;Woodburne, 1977; Archibald et al., 1987;Pascual and Ortiz Jaureguizar, 1990).

One of the most recent renovations in SouthAmerican biostratigraphy was the revisionand isotopic calibration of the CasamayoranSALMA. The Casamayoran was previouslyconsidered an early Eocene mammal record inSouth America (55–50 Ma; Marshall et al.,1983). Cifelli (1985) divided the Casamayoraninto two subages: Vacan, the older, andBarrancan, the younger. Recently, the geo-chronology of the Casamayoran SALMA hasbeen revised at the locality of Gran Barranca(Barrancan subage), south-central ChubutProvince. Several 40Ar/39Ar dates as well as

magnetic polarity stratigraphy from GranBarranca indicated a much younger age thanpreviously recognized for the Barrancan sub-age levels, with an age ranging from 37.60–35.69 Ma (Kay et al., 1999). This indicatesthat the Barrancan is of late Eocene age. Morerecent calibrations indicated an age of about38.5 Ma for the upper boundary of theBarrancan levels, and 41.5 Ma for the base(Madden et al., 2005). There are no publisheddates for sediments deposited during the older,‘‘Vacan’’ subage of the Casamayoran, al-though Carlini et al. (2005: fig. 1) suggesteda time interval of ca. 44–45 Ma for it.

These new findings represent a majorchange regarding South American biochro-nology. During most of the second half of the20th century, the Casamayoran (Barrancanplus Vacan) SALMA was regarded as earlyEocene (e.g., Simpson, 1935b). Thus, theabove-mentioned revisions have left a faunalgap in the early Eocene record of SouthAmerican mammals. This gap is partiallyfilled by the new faunas from the ChubutRiver region, discussed below.

Lower in the Paleogene sequence, theuppermost Salamanca Formation and thewhole Rıo Chico Group (Legarreta andUliana, 1994) are present in several localitiesof Chubut and Santa Cruz provinces, wherethey underlie the Sarmiento Group. They havelong been considered Paleocene in age(Simpson, 1948, 1967a, b). Marshall et al.(1981) correlated the Hansen Member(‘‘Banco Negro Inferior’’) of the SalamancaFormation (Andreis et al., 1975), and theoverlying sediments of the Rıo Chico Groupwith Chron 26r, which corresponds to atemporal range between 61.70 6 0.2 and

2 AMERICAN MUSEUM NOVITATES NO. 3638

58.70 6 0.2 Ma (Gradstein et al., 2004).However, two localities of the Banco NegroInferior have been correlated with Chron 27r(Somoza et al., 1995), i.e., between 63.20 and62.0 Ma (Gradstein et al., 2004). Because ofthe original correlation with the Paleocenefaunas of the Bolivian locality of Tiupampa(Muizon, 1991), the Banco Negro Inferior wasoriginally assigned to the Tiupampan SALMA(Pascual and Ortiz Jaureguizar, 1990). How-ever, Bonaparte et al. (1993) named the newPeligran SALMA on the basis of the distinctmammal assemblage present there. Relativeages of the Peligran and Tiupampan SALMAshave been under intense debate (see Pascualand Ortiz Jaureguizar, 1990; Bonaparte et al.,1993; Gelfo, 2006).

Above the Salamanca Fm. various levels ofthe Rıo Chico Group crop out, mostly insoutheastern Chubut and in northeasternSanta Cruz provinces. Simpson (1935b) rec-ognized ‘‘faunal zones’’ in the region of SanJorge Basin, southeastern Chubut Province,representing distinct faunal episodes in theearly Tertiary: from oldest to youngest thesewere the ‘‘Carodnia faunal zone’’, the ‘‘Kibeni-khoria faunal zone’’, and the ‘‘Ernestokokeniafaunal zone’’. Legarreta and Uliana (1994; seealso Bond et al., 1995) presented a newlithostratigraphy naming the formationsPenas Coloradas, Las Flores, and KoluelKaike, respectively, corresponding to thealready mentioned faunal zones. FollowingBond et al. (1995), these episodes represent atleast three discrete SALMAs, from oldest toyoungest, a post-Tiupampan or post-PeligranSALMA, Itaboraian (Kibenikhoria faunalzone, Las Flores Formation and locality),and Riochican (Ernestokokenia faunal zone),leaving the Carodnia faunal zone as a fourthepisode between the Peligran and Itaboraian,poorly understood and not sufficiently knownto justify naming a new SALMA. Thesuggested age for the Riochican SALMAwas between 58.5 and 55 Ma (Pascual andOrtiz Jaureguizar, 1991). An important limi-tation—as noted by Bond et al. (1995)—is thedifficulty of recognizing these SALMAs out-side the region, even elsewhere in Patagonia.

In brief, taking into account the inferrednumerical ages for the Riochican SALMA andthe Vacan subage of the Casamayoran

SALMA, there seems to be an impressive 10million year time gap between them—i.e.,55 Ma for the top of the Riochican, and45 Ma for the base of the Vacan. Ongoingwork addresses this ‘‘black hole’’ in ourknowledge of the South American Paleogenefaunal successions in two ways: first, we reviewthe previously inferred ages for the whole RıoChico succession (Raigemborn et al., in prep-aration); second, we are prospecting Paleogenelevels outside the San Jorge Gulf region (whichcontains no fossiliferous levels representing thistime gap as currently known).

The present work represents the first of aseries of contributions that propose a newapproach to the problem. Here we describetwo fossil mammal localities of late earlyEocene age from western Patagonia, fillingpart of the current early to middle Eocene gapin the South American fossil record. On thebasis of these localities, we suggest they mayrepresent a new biochronological unit, one ofthe most diverse mammalian faunas known upto now from South America.

ABBREVIATIONS AND TERMINOLOGY

LIEB-PV, Laboratorio de Investigacionesen Evolucion y Biodiversidad–VertebratePaleontology Collection, Facultad de Cien-cias Naturales, Sede Esquel, UniversidadNacional de la Patagonia ‘‘San Juan Bosco’’;MLP, Museo de La Plata; AMNH, AmericanMuseum of Natural History. The dentition isreferred with the letters i/I, c/C, p/P, and m/Mfor lower and upper incisors, canines, premo-lars, and molars, respectively, followed by thecorresponding number, while an ‘‘x’’ refer to atooth of uncertain position.

GEOGRAPHIC SETTING

The new fossiliferous localities, namedLaguna Frıa and La Barda, are the western-most Paleogene mammal-bearing sites inPatagonia. They are located in northwesternChubut Province, Argentina, near the town ofPaso del Sapo, along the south side of themiddle Chubut River (fig. 1). The area issurrounded by the Sierras de Huancache(northeast), Sierras de Cutancunue (south),and Sierras de Taquetren (east).

2009 TEJEDOR ET AL.: EOCENE MAMMALS FROM WESTERN PATAGONIA 3

Laguna Frıa(42u43931.50S, 69u51936.10W, 844 masl)

Laguna Frıa is located within Estancia SanRamon, a farm owned by Mr. RafaelNicoletti, about 170 km northeast of the cityof Esquel and 28 km west of Paso del Sapo(fig. 1, #1). The fossil site was discovered inthe 1950s by Rosendo Pascual, who collecteda small sample of specimens currently housedin the Museo de La Plata. Some of thesparnotheriodontid litopterns described belowwere collected by him. In September, 1999,during a visit to Estancia San Ramon, severalspecimens of mammals collected in LagunaFrıa were donated by Mrs. Coca San Martın,a local resident and former owner of the farm.In addition, successive field trips to LagunaFrıa and La Barda (see below) have provided

hundreds of vertebrate specimens, especiallymammals. Some material was collected on thesurface, but most was obtained by screen-washing of about 3 tons of sediments andsubsequent sorting in the laboratory.

La Barda(42u46948.50S, 69u51943.30W; 1056 masl)

This new locality is in Estancia 26 de Mayo,property of the family of the late Mr. JuanPedro Grenier, 195 km northeast of Esqueland 28 km southwest of Paso del Sapo (fig. 1,#2). It was discovered in December 2001 andfieldwork was carried out during the followingaustral summers until February 2005.Hundreds of mammals were also collectedthere, mostly fragmentary, both by handpicking and dry screening of sediments.

Fig. 1. Location map showing both fossiliferous localities of Paso del Sapo and the remaining knownPaleogene localities of central Patagonia discussed in the text. 1. Laguna Frıa; 2. La Barda; 3. Las Flores; 4.Gran Barranca; 5. Canadon Vaca; 6. Canadon Hondo; 7. Bajo Palangana; 8. Punta Peligro; 9. CerroRedondo; 10. Cerro Pan de Azucar.


STRATIGRAPHYAND GEOCHRONOLOGY

STRATIGRAPHIC CONTEXT

Aragon and Mazzoni (1997) reviewed thegeology and stratigraphy of the MiddleChubut River Volcanic-Pyroclastic Complex.The regional geology, stratigraphy, geochem-istry, petrogenesis, and paleobotany of thiscomplex have been studied by Petersen (1946),Archangelsky (1974), Volkheimer and Lage(1981), Lage (1982), Rapela et al. (1984),Aragon and Romero (1984), Aragon et al.(1987), Mazzoni and Aragon (1985), andMazzoni et al (1989). These studies indicatethat the complex is of Paleocene-Eocene age,and includes a variety of volcaniclastic,intrusive, pyroclastic, and extrusive rocksdeposited over several million years. Agreat variety of volcanogenic bodies suchas ignimbrites, domes, lava flows, necks,intrusives, tuffs, and volcaniclastic deposits(of predominantly lacustrine origin), all ofthem frequently interbedded, has been de-scribed in the region. These deposits werepreviously grouped in the Huitrera and ElMirador formations by Volkheimer andLage (1981) and Lage (1982). Later, Aragonand Mazzoni (1997) defined 12 formal strati-graphic units within the whole complex.Three of them are relevant for this study:Ignimbrita Barda Colorada Formation (IBC),Tufolitas Laguna del Hunco Formation(TLH), and Andesitas Huancache Forma-tion (AH). The TLH bears an extraordinaryfossil flora exposed at a few localities;this flora was recently revised by Wilf et al.(2003).

The Ignimbrita Barda Colorada Formationoverlies the latest Cretaceous/earliest PaleoceneLefipan Formation (fig. 2). It represents amajor volcanic event (in volume more than100 km3) that deposited a large 80 m thickignimbritic plateau related to the formation ofa 25 km wide caldera. The Tufolitas Lagunadel Hunco Formation (TLH) conformablyoverlies the IBC Formation (fig. 2) andcorresponds to the lacustrine deposits withinthe caldera. The IBC is interstratified withseveral other postcaldera volcanic units(Andesitas Estrechura, Ignimbritas Rulos,Riolitas Gualjaina, and Vitrofiros Huitrera;

see Aragon and Mazzoni, 1997). In this work,we propose that one of the fossiliferouslocalities, Laguna Frıa, may correspond tothe TLH deposits. Finally, the AndesitasHuancache are predominantly lavas alter-nating with intercalated tuffs, volcanic agglom-erates, and sandstones. Together with the IBC,the AH are the thickest deposits of thecomplex. The second fossiliferous localitydescribed here, the La Barda local-ity, occurs within the AH interbeddedtuffs.

The levels of Laguna Frıa overlie uncon-formably the IBC (Aragon and Mazzoni,1997) at the ignimbritic plateau outside thecaldera and are unconformably overlain bylava flows of the AH (upper member; fig. 2).The AH at this locality includes a sequence ofalkaline basalts with a few interbedded tuffs.The extrusive centers of these flows are to theNW (Cerro Negro, in Piedra Parada). Thedistribution and geometry of the Laguna FrıaTuffs are filiform, and were controlled by thepaleogeography of the fluvial valleys. Runningto the southeast, this large paleovalley systemdeveloped first over the IBC and then directlyover the Lefipan Formation, in the vicinity ofLa Barda, and, finally, it cut into the Paso delSapo Formation near Cerro Gorro Frigio, inits southernmost extreme.

Figure 2 is a stratigraphic column ofLaguna Frıa, where the Laguna Frıa Tuffsfill a paleovalley cut in the IBC and are latercut by another paleovalley filled with basaltsof the AH. Further up in the basaltic AH filloccur a few interbedded tuffs such as LaBarda.

GEOCHRONOLOGY

40K/40Ar dates indicate an age of 58.6 Mafor the IBC (see Archangelsky, 1974, correctedwith 1978 decay constants). The intracalderalake beds (TLH) at the locality with the leafflora have several 40Ar/39Ar dates of the tuffsthat indicated ages near 52 Ma (Wilf et al.,2003). Since the TLH overlies the IBC, these40Ar/39Ar ages suggest that the IBC must beolder than 52 Ma.

At Laguna Frıa a 52.05 6 0.23 Ma40Ar/39Ar age was obtained from an ignim-brite that conformably overlies the IBC


(Gosses et al., 2006, sample 1). In turn, a basalignimbrite in the fossil-bearing tuffs of theextracaldera valley-fill deposits is dated at49.51 6 0.32 Ma (Gosses et al., 2006). Finally,the overlying AH basalt dated at 47.89 61.21 Ma using the 40Ar/39Ar method (Gosseset al., 2006, samples 2 and 3, taken about

100 meters above the ignimbrite sampled anddated at 49.51 6 0.32 Ma) are found withinthis member between the valley-fill ignimbriteand the AH basalt. Thus, the Laguna Frıamammal-bearing tuffs overlie unconformablythe IBC and are covered unconformably bythe AH alkaline basalt, meaning their age is

Fig. 2. Stratigraphic column including the localities of Laguna Frıa and La Barda.


close to the 49.51 6 0.32 Ma ignimbrite,younger than the 52.05 6 0.23 Ma ignimbriteand older than the 47.89 6 1.21 Ma AHbasalt.

The La Barda Tuffs interbedded withthe AH lava flows are somewhat younger asthey occur above the 47.89 6 1.21 Ma basalt.The Andesitas Huancache to the west haveyielded three 40K/40Ar dates near 43 Ma(Mazzoni et al., 1991). The La Barda Tuffsunderlie the 43 Ma lava flows of the AH;as discussed below, and judging from thefaunal similarities between the LagunaFrıa and La Barda assemblages, it is reason-able to assume a 45–47 Ma age for thedeposition of the La Barda mammal-bearingtuffs.

PRELIMINARY TAXONOMY

The taxonomy presented below is prelimi-nary because many of the taxa will requiredetailed analysis, naming, description, andcomparisons. The preliminary taxonomy giv-en below is useful to understand the unique-ness of these new early Eocene mammalianassemblages. Most of the new taxa will bedescribed in depth and named elsewhere.However, the description of the new speciesPolydolops unicus, sp. nov., is necessarybecause its first occurrence will be used todefine this unit.

Order ‘‘Didelphimorphia’’ Gill, 1872

Family Peradectidae Crochet, 1979

Gen. et sp. nov. 1

Figure 3A

One upper and three lower molarsfrom Laguna Frıa are referred to this newtaxon (LIEB-PV 1031, a left M?3). Theupper molar has a reduced stylar shelf,shallow ectoflexus, vestigial StC and StD,moderately developed StB, centrocrista linearand paraconule, and metaconule vestigial orabsent. The lower molars match the upper,and they also present peradectoid traits. Theyshow a vestigial postcingulum and lesstwinned entoconid and hypoconulid, com-pared to other peradectids. Trigonids andtalonids are subequal in length but talonidsare wider.

Family Caroloameghiniidae Ameghino, 1901

Gen. et sp nov. 2

Figure 3B

Three lower molars collected at LagunaFrıa and one upper molar from La Barda(LIEB-PV 1098, a left MX) are referred to thisnew taxon. It closely anticipates the molarstructure of Caroloameghinia in the followingtraits: trigonid approximately one third thesize of the talonid; protoconid and metaconidof similar height and development; reducedparaconid; well-developed, high and labiolin-gually compressed entoconid; very reducedhypoconulid that is not twinned with theentoconid; and reduced anterobasal cingulum.It differs from Procaroloameghinia andCaroloameghinia in the more reduced paraco-nid, more anteroposteriorly compressed trigo-nid, better-developed entoconid and talonidbasin, and absence of crenulations in themolar surface. LIEB-PV 1098 is an uppermolar tentatively referred to this new taxon; itshows characters that also anticipate themorphology of Caroloameghinia. The molaris badly worn but it presents a linearcentrocrista, short preparacrista, paracone,and StB close to each other, and postmeta-crista transverse to the dental axis. Because ofwear, it is not possible to confirm the presenceof a paraconule and metaconule, but at least ametaconule was likely present due to the‘‘angulate’’ wear pattern on the protoconalarea. StB is the largest cusp of the stylar seriesand apparently the StC was absent.

This new taxon shares all the diagnosticcharacters of the Caroloameghiniidae, i.e.,brachydont crowns and bunodont cusps,poorly developed crests, reduced anterobasalcingulum, postcingulum absent, anteroposte-rior compression of the trigonid, and well-developed talonid and entoconid. In addition,the lower molars are similar in size toCaroloameghinia mater. In general, this taxonshows an intermediate pattern betweenProcaroloameghinia and Caroloameghinia.

Family ?Caroloameghiniidae

This taxon is represented by a singlespecimen, an isolated, left mx talonid (LIEB-PV 1099) from La Barda. The bunoid aspect


Fig. 3. Marsupials from Laguna Frıa (LF) and La Barda (LB). A, Peradectidae gen. et sp. nov., LIEB-PV 1031 (LF); B, Caroloameghiniidae gen. et sp. nov., LIEB-PV 1098 (LF); C, Peradectoidea gen. et sp.nov., LIEB-PV 1097, left M3 (LB); D, Protodidelphis sp. nov., LIEB-PV 1091, left M?3 (LB); E,Pauladelphys sp. nov., LIEB-PV 1123, m2 in a fragment of right dentary (LF); F, cf. Itaboraidelphys sp.,LIEB-PV 1064, an isolated right m2 or m3 (LF); G, Paucituberculata gen. et sp. nov. 1, LIEB-PV 1135, a leftmaxillary fragment with M2–3 and part of M4 (LF); H, Sparassodonta, Hathliacynidae, gen. et sp. nov.LIEB-PV 1036, M?3 in a maxillary fragment (LF); I, Eomicrobiotherium sp., LIEB-PV 1040, a right m?3(LF); J, Palangania sp., LIEB-PV 1106, left M?3 (LB); K, Gashternia ctalehor, LIEB-PV 1132, a right M4(LB).


of the cusps is noted, as well as the largeentoconid and the presence of supernumerarycusps anterior to the entoconid and hypocon-id. These traits are characteristic of theCaroloameghiniidae, but the conical shape ofthe entoconid and the presence of a vestigialpostcingulum are not seen in other caroloa-meghiniids. Its size does not match with theabove-described molars.

Family Incertae sedis

Gen. et sp. nov. 3

Figure 3C

Several upper and lower molars of this newtaxon were collected at both localities of Pasodel Sapo. The molars are brachydont andbunodont. Upper molars (e.g., LIEB-PV 1097,a left M3; fig. 3C) have a robust protocone,StB and StD relatively conical, vestigial‘‘StC’’, poorly developed ectoflexus, and con-ules not winged. The centrocrista is linear andlow. As in peradectians, there is no differencebetween the relative height of the stylar shelfand the trigon basin. The lower molars have areduced anterobasal cingulum and a reducedhypoconulid, and they lack a postcingulum.Trigonid and talonid are subequal in length.The talonid basin is wide and entoconid andhypoconid are subequal in height and devel-opment; the hypoconulid is small. The widetrigon and talonid basins and the robustprotocone suggest a strong adaptation towardgrinding. Judging from this morphology, thisnew taxon exhibits an omnivorous, or omniv-orous-frugivorous adaptation.

Family Protodidelphidae Marshall 1987

Protodidelphis, sp. nov.

Figure 3D

This new species of Protodidelphis is wellrepresented by several lower and upperisolated teeth from La Barda. It differs fromother species of the genus mostly in its smallersize and less bunoid aspect. The upper molars(e.g., LIEB-PV 1097, a left M3; fig. 3D) have awell-developed metaconule and the crestjoining the StB and StD is straight, unlikethe Itaboraian species of the genus. The lowermolars have a hypoconulid slightly more de-

veloped in m3–4 than in other Protodidelphisspecies. The overall crown surface is simpleand devoid of cluttering crests; the stylarregion is not specialized for ‘‘crowding’’against the paracone and metacone; thecentrocrista is linear and there is no specialelevation of the stylar shelf relative to thetalon surface. The lower molars have normaltrigonid vs. talonid proportions; the paraconidis not reduced or otherwise specialized as tosize or location; the metaconid and entoconiddo not develop strong opposing crests; theentoconid is basically conical and isolated;the hypoconulid is located near, but isolatedfrom the entoconid, and connected to thehypoconid.

Protodidelphis cf. Protodidelphis, sp. nov.

About a dozen isolated upper and lowerteeth are here tentatively referred to theabove-described new species of Protodidel-phis, but this material comes from LagunaFrıa whereas the Protodidelphis sp nov. ischaracteristic of La Barda. Because only someof this material is well preserved, a preciseattribution is difficult. Some minor differencesare observed: the LF material is slightly largerin size, with more inflated molars, moredeveloped metaconule, StB and StD closer toeach other, and the preparacrista ends labiallyin a position closer to the anterolingual side ofthe StB in M2–3.

Protodidelphis, sp.

Two isolated lower molars (LIEB-PV 1092,isolated left m?1; LIEB-PV 1142, isolatedleft m?3) clearly differ from the otherProtodidelphis specimens recorded in Pasodel Sapo. These came from La Barda andare about twice the size of Protodidelphis, sp.nov. One of them, LIEB-PV 1092, is stronglyworn, but the talonid appears to be shorterthan in other species of Protodidelphis, and thehypoconid is less projecting labially. The othermolar, LIEB-PV 1142, differs in a few details(i.e., more projecting hypoconid, paraconidcloser to the metaconid, protoconid morerobust), but it is certainly from a differentlocus in the molar series. However, bothmolars are assigned to Protodidelphis on the


basis of their bunoid pattern, well-developedentoconid, relatively low paraconid, re-duced hypoconid, and anterobasal cingulum.Because of the size and morphology of thetalonid, they cannot be referred to anyProtodidelphis species known up to now,including those listed above.

Family Derorhynchidae Marshall, 1987

Genus Pauladelphys Goin et al., 1999

Pauladelphys, sp. nov.

Figure 3E

This new species of Pauladelphys is wellrepresented by dentition, maxillae, and man-dibles mostly from Laguna Frıa and a fewspecimens from La Barda. It differs fromPauladelphys juanjoi, from the AntarcticPeninsula, in several features of the molarseries. The lower molars have a cristid obliquamore parallel to the dental axis; paraconid lessreduced and anteroposteriorly compressed;anterobasal cingulum narrower; labial slopeof the entoconid almost flat (LIEB-PV 1123,fragment of right dentary with complete m2;fig. 3E). Upper molars show a larger metaco-nule; StB less posteriorly placed; paraconefarther from the StB. This is a fully tribo-sphenic taxon in which the molars aresharply crested. All stylar cusps are present;StB is sometimes very large; the centrocristais V-shaped. The stylar shelf is elevatedabove the talon basin. The paraconule ispresent, but small and variably winged; themetaconule is larger and also variably winged.The lower molars also are fully tribosphenicand crested, with the cusps subpyramidal. Thisnew species of Pauladelphys is almost equalin size to the type species of the genus.However, several traits (e.g., StB less displacedposteriorly, less reduced and compressedanteroposteriorly paraconid) suggest thatPauladelphys sp nov. is more generalized thatP. juanjoi.

Genus Derorhynchus Paula Couto, 1952

Derorhynchus cf. D. minutus Goin et al., 1999

This taxon is represented by eight specimensfrom Laguna Frıa. The lower molars closelyresemble, in size and structure, those of

Derorhynchus minutus, from the late earlyEocene of the La Meseta Formation inAntarctica. Lower molars have all character-istic features of the Derorhynchus species:small paraconid, short talonid, and high,spirelike entoconids. The Laguna Frıa speci-mens are almost identical in size to those ofthe La Meseta Fm.

Derorhynchus sp.

Though scarce, two specimens (LIEB-PV 1102, right m4; LIEB-PV 1140, iso-lated left talonid) from Laguna Frıa canbe confidently referred to the genus Dero-rhynchus, as they share most of the lowermolar pattern (see above) with species of thisgenus.

Family Sternbergiidae McKenna and Bell1997

Genus Marmosopsis Paula Couto 1962

Marmosopsis sp.

The referred specimens are two right mx(LIEB-PV 1286, and LIEB-PV 1287), bothfrom La Barda. We tentatively assign them toMarmosopsis sp. for the following reasons:laterally compressed lower molars, propor-tionally long talonids, and slender, thoughsharp, trigonid cusps.

cf. Itaboraidelphys Marshall and Muizon, 1984

cf. Itaboraidelphys sp.

Figure 3F

All materials referred to this species arefrom Laguna Frıa: illustrated is an isolatedright m2 or m3 (LIEB-PV 1064), and addi-tional referred materials include an isolatedleft metastylar area (M1 or M2; LIEB-PV1066); isolated lower left premolar (LIEB-PV1067); fragment of left upper molar (Mx;LIEB-PV 1110); and right metastylar frag-ment (LIEB-PV 1075).

In size and overall morphology, thesespecimens resemble the pattern seen in theItaboraian-aged Itaboraidelphys, previouslyknown from Itaboraı (Brazil) and Las Flores(Argentina). In the upper molars, the post-metacrista is well developed and trenchant;


premolars are laterally compressed, and mo-lars have unreduced talonids and well-devel-oped paracristids.

‘‘Didelphimorphia’’ indet.

Gen. et sp. indet. A

Three upper molars from Laguna Frıa aredifficult to assign. LIEB-PV 1042, possiblyan M1, is completely preserved. This is asubtriangular tooth, canted anterolingually.The protocone is pointed anterolingually;paraconule and metaconule, respectively, areabout half-way along the pre- and post-protocristae, and do not closely abut thelingual bases of the paracone and metacone;they do not appear to have been stronglywinged. The preparacrista extends past theanterior base of the paracone to reach asmall cuspule at the lingual base of StA.Paracone and metacone are well separated,about equally tall, but the metacone issomewhat more massive than the paracone.The centrocrista is linear, but weakly ex-pressed. The talon basin is deep and sepa-rated by the centrocrista from the elevatedstylar shelf. The stylar shelf is narrow andbears a complete complement of stylar cusps,all relatively small and much lower thanthe paracone or metacone. The ectoflexusis virtually absent. The postmetacrista isstrongly crested and performed a shearingfunction. The elevation of the stylar shelfshows the derived nature of this toothrelative to a peradectian. Apparently theconnection of the preparacrista to StB ratherthan to StA is a non-microbiotherian char-acter.

Order Paucituberculata Ameghino, 1894

Family indet.

Gen. et sp. nov. 4

Figure 3G

A left maxillary fragment with M2–3 andpart of M4 (LIEB-PV 1135; fig. 3G) wascollected in La Barda. The protocone is thelowest and widest cusp of the trigon; theparacone is small and lower than the meta-cone, the latter is pointed and has a metacristaposteriorly, longer than the paracrista in both

molars. Paraconule and metaconule are devel-oped.

Two additional specimens from La Bardaare here referred tentatively to the same taxon.LIEB-PV 1137 is a well-preserved mandibularfragment with one lower molar and roots ofan additional molar. The molar probablycorresponds to an m2 or m3. Trigonid andtalonid length is subequal; the paracristid iswell developed and the metacristid has a deepfovea; paraconid and metaconid are close toeach other, more than is expected for didel-phimorphians. The anterobasal cingulum isnarrow. LIEB-PV 1138 is almost identical tothe former, but the metaconid is moreseparated from the paraconid, as occurs inm1s of Paucituberculata.

Gen. et sp. nov. 5

This taxon is represented by one upperand three lower molars from La Barda.The upper molar LIEB-PV 1151 shows amorphology similar to the above-describedPaucituberculata, but larger in size and withcusps more inflated. The protocone andStB are the largest cusps and even moreinflated; the metacone is subequal in sizebut taller than the paracone; the centrocristais deep and its distal part is oriented labialand posteriorly. The metaconule and para-conule are more developed than in Gen. etsp. nov. 4, both winged, but the metaconulelacks the postmetaconular crest. The speci-men LIEB-PV 1101 is a left lower molarthat shows the paraconid and metaconidclose to each other; talonid wider thantrigonid; hypoconid is labially expanded.The specimen LIEB-PV 1136 is most proba-bly a left m4. As in the lower molars of theGen. et sp. nov. 4, the entoconid is com-pressed laterally.

Order ?Paucituberculata

Gen. et sp. indet. B

LIEB-PV 1108 is a left mandible fromLa Barda, with four alveoli and the rootof a hypertrophied and procumbent i1.The mandibular ramus is low in compar-ison with Gen. et sp. indet. A, about half itsheight.


Order Sparassodonta Ameghino, 1894

Family Hathliacynidae Ameghino, 1894

Gen. et sp. nov. 6

Figure 3H

This new taxon is based on LIEB-PV 1036,a maxillary fragment with M?3 (fig. 3H), andLIEB-PV 1037, isolated metastylar portion ofa right M?2, both from Laguna Frıa.Although an additional specimen, LIEB-PV1141, a fragment of a left M?2, was collectedat La Barda, it is here assigned to the sametaxon. LIEB-PV 1036 has a slightly reducedstylar shelf, with an StB still present, conical,and similar in size to the paracone; paraconeand metacone are twinned, with the metaconemuch larger, resulting in a nearly absentcentrocrista. The postmetacrista, althoughbroken, appears to have been well developed.There is a small paraconule, but apparentlythe metaconule was absent or extremelyreduced.

LIEB-PV 1036 is much larger than theoldest known hathliacynids (Allkoquirus aus-tralis, from the early Paleocene of Bolivia, andthe species of Patene, widely distributedbetween the late Paleocene and late Eoceneof Patagonia and Brazil; Muizon, 1991;Marshall, 1978). The difference in heightbetween paracone and metacone, and thereduction of the protocone are surprising incomparison with primitive hathliacynids. Alsodiffering, the StB is not reduced and issubequal in size to the paracone.

A second aspect of major biostratigraphicsignificance is the fact that the upper molarLIEB-PV 1036 is very similar to a fragmentaryupper molar assigned to Borhyaenidae indet.(MLP 79-I-17-5), held in the Museo de LaPlata collection. Although it lacks the proto-cone, most of the tooth is well preserved and iscomparable to the Laguna Frıa molar in theStB dimensions, reduction of the other stylarcusps, width of the stylar shelf, and length ofthe postmetacrista. The major differencebetween the specimens is that, apparently,the Laguna Frıa molar has a larger metacone.This difference, however, does not ‘‘invali-date’’ the potential attribution of both speci-mens to the same genus, and, probably, to thesame species. Specimen MLP 79-1-17-5 wascollected in 1979 at Bajo Palangana, Chubut

Province, by M. McKenna and R. Turnbull,who tentatively correlated those levels with the‘‘?Casamayoran’’ (McKenna and Turnbull,unpublished data). The stratigraphy of BajoPalangana correlates almost completely withthe Rıo Chico Group or Formation.

Family Borhyaenidae Ameghino, 1894

Subfamily Borhyaeninae Ameghino, 1894

cf. Nemolestes

LIEB-PV 1038 is an isolated left m?4 fromLaguna Frıa. The talonid is unicuspid andreduced, approximately 20% of the totallength; the trigonid is formed exclusively bythe paraconid and protoconid. Althoughpartially broken, the paracristid seems to havebeen well developed. The anterobasal cingu-lum is present but weak.

The early representatives of the Sparasso-donta are still poorly known. As an example,there is a citation of ‘‘cf. Nemolestes sp.’’ fromthe Itaboraian of Brazil and Riochican ofArgentina (see Marshall, 1978; Marshall et al.,1983). Also, indeterminate specimens are men-tioned for Itaboraian levels of Itaboraı (Brazil)and Las Flores (Patagonia) (Goin, personalobs.), as well as indeterminate borhyaenidsfrom the Riochican of Cerro Redondo (seeSimpson, 1935b).

Gen. et sp. indet. C

LIEB-PV 1093 is a right m?1 from LaBarda. The trigonid is formed exclusively bythe protoconid and the much lower paraconid;there is no keel basal to the paraconid. Theanterobasal cingulum is vestigial and thepreparacristid is short. The talonid is widerthan the trigonid with only one central cuspand two labial and lingual slopes. The talonidends in a small distal cuspule (hypoconulid?),with a lingual edge ending in a tiny crenula-tion (entoconid?). The presence of a centralcusp in the talonid is a trait also seen inseveral borhyaenines, such as Plesiofelis andPharsophorus, as well as in the proborhyae-nids. The absence of a metaconid characterizesnot only the m1 of proborhyaenids, but alsoall the lower molars of prothylacynines andm1 of borhyaenines.


Order Microbiotheria Ameghino 1887

Family Microbiotheriidae Ameghino 1887

Genus Eomicrobiotherium Marshall 1982

Eomicrobiotherium sp.

Figure 3I

A single specimen of this taxon was foundat Laguna Frıa (LIEB-PV 1040, right m?3). Itis robust, bunoid, with a short talonid which isrelatively narrow, though slightly wider thanthe trigonid; large terminal but labially placedparaconid; protoconid and metaconid alsolarge. The talonid is shorter than the trigonid;the cristid obliqua extends anterolingually tothe rear of the trigonid posterior to theprotoconid. The lingual half of the talonid israised relative to the talonid basin, stronglyblocking the lingual exit of that basin. Theapically broken entoconid is a massive cusp. Abroken wear surface suggests the formerpresence of a hypoconulid posterolingual tothe entoconid, but another broken surfacemay show that this cuspid was present nearthe posterior midline of the tooth. A shortanterior and posterior cingulum is present.

The massive nature of the cusps, theanterior projection of the low paraconidrelative to the higher and more unifiedprotoconid and metaconid, and the tall lingualmargin of the talonid are all very distinctivefeatures.

Gen. et sp. indet. D

This taxon is known from two specimensfrom Laguna Frıa: LIEB-PV 1039, a fragmentof right dentary with the alveoli for i1-m2, andLIEB-PV 1041, a right Mx. The alveoli for theincisors in LIEB-PV 1039 are not staggered asoccurs in i2 of didelphimorphians. The fourincisors appear to have been subequal in size,but i4 was probably smaller. The canine alsowas relatively small. LIEB-PV 1041 does notpreserve the stylar shelf. The paracone andmetacone are similar in size and height, andthe centrocrista is linear, as in all othermicrobiotheriids. The protocone is robustand the trigon basin is wide; small paraconuleand metaconule are present. Precise affinitiesof this taxon are difficult to assess, but therobustness of the molars suggests a possiblerelation with Pachybiotherium acclinum.

Family ?Microbiotheriidae

Gen. et sp. indet. E

LIEB-PV 1094 is an upper right molarlacking the protocone, probably an M4because of the reduced metastylar area andabsence of StD, that was collected at LaBarda. Paracone and metacone are similar insize, but the paracone is slightly taller. Thecentrocrista is linear; the precingulum is shortand narrow. StB and StA are subequal and atiny StC is placed behind the posterior crest ofthe StB.

Order ?Microbiotheria Ameghino, 1887

Gen. et sp. indet. F

Two lower molars from Laguna Frıa andtwo uppers from La Barda are included in thistaxon. The uppers show a linear centrocristaand short postmetacrista. The metaconule ismuch larger than the paraconule; neither iswinged. The protocone is not wide, as seen inCaroloameghiniidae. These upper molars dif-fer from microbiotheriids in having a well-developed metaconule and short postmetacris-ta. On the contrary, the short postmetacristaand relative size of the metaconule suggestaffinities with Caroloameghiniidae. The lowermolars are twice the size of Gen. et sp. indet.E. In the specimen LIEB-PV 1043, probablyan m1, the metaconid is small and placedposterior to the protoconid; the trigonid/talonid width is similar; the entoconid islaterally compressed and close to the metaco-nid; and the hypoconid is robust and does notproject labially; and the hypoconulid is verysmall and nearly centrally placed.

Order Polydolopimorphia Ameghino, 1897

Suborder Hatcheriformes Case et al., 2004

Family Glasbiidae Clemens, 1966

Palangania cf. P. brandmayri Goin et al., 1998

Two lower molars from La Barda (LIEB-PV 1089 and 1090) and one from Laguna Frıa(LIEB-PV 1051) are here assigned to thistaxon. Trigonid and talonid lengths aresimilar, but the talonid is wider. The labialside is clearly twice the height of the lingualside. The trigonid shows a distinctively low


protoconid and a small crest joining linguallythe paraconid and metaconid; thus the trigo-nid basin is closed. The hypoconid is broadand the hypoconulid is relatively central; theanterobasal cingulum is absent, as is thepostcingulum.

These molars resemble Palangania brand-mayri in having low trigonid cusps, similar inheight; metacristid is not vertical but forms aninclined surface toward the talonid; hypocon-ulid reduced and separated from the entoco-nid; entoconid large and bulbous. Thesemolars are nearly the same size as those ofthe type species of Palangania.

Palangania sp.

Figure 3J

A single specimen (LIEB-PV 1106, left M?3;fig. 3J), an upper molar from La Barda, iscomplete but worn. The protocone is aprominent cusp and the trigon basin is deepand wide. The stylar shelf is reduced and StBand StD are placed close to the paracone andmetacone, respectively; a lower StC is present.The centrocrista is almost linear, somewhatcurved labially; the preparacrista ends on theanterolingual side of the StB and the post-metacrista is short. Due to the wear, it is notpossible to confirm the presence of a meta-conule, but a paraconule was already pre-sent. Also, the StC is relatively larger and thestylar shelf is more developed labiolingually.Although smaller and more generalized, thismolar resembles the M3 of Palangania brand-mayri.

Suborder Bonapartheriiformes Goin andCandela, 2004

Family Gashterniidae Marshall, 1987

Gashternia ctalehor Simpson, 1935

Figure 3K

The holotype of this species, AMNH 28533,a right mandibular fragment with m1–2partially preserved is from the upperPaleocene of Patagonia. Several upper andlower molars attributed to this taxon werefound at La Barda. Gashternia differs fromother Polydolopimorphia in having lowermolars with trigonid and talonid divided by

a deep flexus anterior to the cristid obliqua.The metaconid is higher than the protoconidin m2–4 and becomes fused to the metaconidfrom m1 to m4. The anterobasal cingulum andhypoconulid are vestigial. Upper molars (e.g.,LIEB-PV 1132, right M4; fig. 3K) have a deeplingual flexus separating the protocone fromthe hypertrophied and lingually displacedmetaconule. StB and StD are the mostdeveloped stylar cusps while StC is lacking inall molars. The postmetaconular crest reachesthe labial edge forming a wide sulcus.

The selenodont condition of Gashterniamakes it one of the most singular SouthAmerican marsupials. In the original descrip-tion, Simpson (1948: 69) wrote:

this peculiar little jaw is quite unlikeanything else known to me. … There issome suggestion that it may be a marsupial,chiefly the fact that the probabilities some-what favor the presence of only threepremolars, but this is not certain.

The material from Paso del Sapo led usto understand the morphology of all mo-lars, including the uppers, and stronglysupports the inclusion of Gashternia in theMetatheria.

Suborder Polydolopiformes Kinman, 1994

Family Polydolopidae Ameghino, 1897

Subfamily Polydolopinae Ameghino, 1897

Genus Polydolops Ameghino, 1897

Polydolops unicus, sp. nov.

HOLOTYPE: LIEB-PV 1252, right maxillaryfragment with P3–M3 (fig. 4a). P3 width 52.96; P3 length 5 2.46; M1 width 5 3.60; M1length 5 2.89; M2 width 5 4.41; M2 length 52.6; M3 width 5 2.41; M3 length 5 2.24.

ETYMOLOGY: From the Latin unicus,‘‘unique’’, recognizing the exceptionally de-rived morphology of its second upper molars.

REFERRED SPECIMENS: The holotype andLIEB-PV 1240*, left maxillary fragment withM2–3; LIEB-PV 1241*, left M1, LIEB-PV1242*, right M1, LIEB-PV 1243*, right M1,LIEB-PV 1244*, right, broken M1; LIEB-PV1245, left maxillary fragment with M1–2;LIEB-PV 1246, left M1; LIEB-PV 1247, leftM2; LIEB-PV 1248, left M2; LIEB-PV 1249,


left M2; LIEB-PV 1250, left M2; LIEB-PV1251, right maxillary fragment with P3–M3;LIEB-PV 1253, right M1; LIEB-PV 1254,right M1; LIEB-PV 1255, right M1; LIEB-PV 1256, right, broken M2; LIEB-PV 1257,right M3; LIEB-PV 1258, right M3; LIEB-PV1212*, left dentary with broken m1, completem2, and roots of m3; LIEB-PV 1217*, rightdentary with m1–3; LIEB-PV 1259*, leftmandible with m1–2 and roots of p3; LIEB-PV 1260*, left mandible with m2–3; LIEB-PV 1261*, left m2; LIEB-PV 1262*, rightmandible with m1–2; LIEB-PV 1263, leftmandible with m1–2; LIEB-PV 1265, left m2;LIEB-PV 1266, left, broken m2; LIEB-PV1267, right mandible with broken p3, completem1–2, and roots of m3; LIEB-PV 1268, rightmandible with m2; LIEB-PV 1269, rightmandible with m2; LIEB-PV 1270, rightmandible with m2; LIEB-PV 1271, rightmandible with broken m1, complete m2, androots of m3; LIEB-PV 1272, left m1; LIEB-PV

1273, right m1; LIEB-PV 1274, right m1;LIEB-PV 1275, right m2; LIEB-PV 1276,broken right m2; LIEB-PV 1277, right m3;LIEB-PV 1278, right m3.

GEOGRAPHIC AND STRATIGRAPHIC PROV-

ENANCE: Specimens marked above with anasterisk (*) come from Laguna Frıa, while theremainder are from La Barda; TufolitasLaguna del Hunco Formation, early middleEocene, western Patagonia.

DIAGNOSIS: Polydolops unicus (fig. 4) dif-fers from other species of Polydolops in thefollowing characters: large size, althoughsmaller than P. mayoi and P. abanicoi; shorterface, and higher and more robust maxillae andmandibles; M1 comparatively shorter; M2broader than M1; the metacone and StB ofM2 are fused and hypertrophied, thus forminga single cusp strongly projecting over theocclusal plane of the upper molars; m1–2 (andprobably m3) relatively small and short inrelation to the size of the mandibular corpus;

Fig. 4. Polydolops unicus sp. nov., the most unusual and representative mammal of Paso del Sapo.Holotype, LIEB-PV 1252, right maxillary fragment with P3–M3 (LF) in A, occlusal, and B, lingual views; C,LIEB-PV 1277, right m3 (LB). Scale bar 5 1 mm; D, LIEB-PV 1271, right m2 (LB).


m1–2 hypoconid placed more anteriorly thanin P. rothi.

DESCRIPTION: Abundant upper and lowerteeth, mandibles, and maxillae of this newtaxon are preserved, coming from bothlocalities at Paso del Sapo. This new speciesis the most specialized polydolopine known todate; the functional significance of theseadaptations are under study.

The holotype preserves most of the maxillaand cheek teeth. The maxilla is high in relationto other polydolopines, and it has a moder-ately developed infraorbital foramen locatedabove the root of P3. The suture line betweenthe maxilla and the anterior part of the jugal ispreserved, showing that the jugal was verti-cally high. P3 is mesiodistally short andbuccolingually wide, nearly as wide as theM1. The crown shows a large principal cuspand a smaller one anteriorly placed. The majorcusp has two crests, anterior and posterior, andtwo ‘‘ridges’’, labial and lingual. The crests arenot sharp compared to the ridges. The poste-rior root is broad, probably twice the size of theanterior root. A little-developed talon is presentposterolingually. M1 is proportionally shorterand wider than P3, much wider in the posteriorhalf. There are two cusp rows labially, notaligned but with an irregular pattern, especiallyin the more labial row; both rows join in arelatively large StB. A reduced paracone is seenon the lingual side of the StB. In the stylar shelf,the internal row is formed by the StC and StDaligned and subequal in size and height, and theStE somewhat lower than the StB. A metaconeis observed between StD and StE, with the basefused to these stylar cusps, and the metacone isalmost the height of StE. The labial row isformed by four accessory cuspules. M1 exhibitstwo lingual lobes, with a paraconule in theanterior one. Three subequal cusps are ob-served in the anterior half of the posterior lobe:the first is probably the protocone, followed byan accessory cusp, and the third is probably themetaconule, but the homologies are difficult toassess.

M2 is an odd tooth, very derived andunique among the Metatheria. Its degree ofspecialization is even more surprising consid-ering that M1 and M3 do not show the samespecialization. The unusual buccolingualwidth is clearly greater than in M1, and more

than twice that of M3. The lingual edge of M2is aligned with the lingual edges of M1 andM3, thus leaving the labial edge projectingbeyond the labial edge of M1. Anothersurprising character is the possible presenceof four roots, with a large lingual and threelabial roots. It is possible that the anterolabialand centrolabial roots are parts of the sameroot with two lobes. But the most remarkabletrait is the enormous cusp placed centrola-bially; this hyperthrophied tooth has modifiedthe total volume of the tooth as well as thesupporting root; as a result, the labial rootshave developed an additional lobe. This hugecusp appears to be formed by the fusion of themetacone and StD. The lingual margin of M2is relatively linear with poorly developedparaconule and metaconule that have meta-conular crests. The trigon basin is rugged. TheM3 is reduced and simplified compared toM1–2, being generally subtriangular in shape,longer lingually than labially.

There is remarkable variability in the sizeand robustness of the mandibles, probablysuggesting sexual dimorphism. The anteriorpart of the mandibles is not preserved in anyspecimen of P. unicus, thus there is noinformation on the incisors and anteriorpremolars. The p3 is only known in twospecimens but only the base was preserved; itwas apparently short and robust. The lowermolars are compact, robust, and slightlyhypsodont labially (labial side clearly higherthan the lingual side). The m1–2 are subequalin length and width, while m3 is longer andnarrower. The occlusal surface was crenulat-ed. The m1 shows a very reduced and shorttrigonid, with two low cusps. Behind thetrigonid, there are three lingual and threelabial cusps. The labial cusps are shallow androbust, the posterior (hypoconid) being themost robust. The m2 is shorter and shallowerthan the m1, with just four lingual and fourlabial cusps, among which the metaconid (asin other polydolopines) is the highest andmore robust. The most striking trait in m2 isthe anterior position of the hypoconid; thistrait was incipient in Polydolops rothi, but hasa high degree of specialization in P. unicus.This trait clearly distinguishes P. unicus fromany other polydolopine species. In polydolo-pines, the posthypocristid is almost parallel to


the posterior margin of the tooth, slightlycurving forward to meet the hypoconid. Tothe contrary, in P. unicus (and in a much lesserdegree in P. rothi), the posthypocristid isoblique to the dental axis, slightly concave.This odd morphology is certainly related tothe occlusion with the huge cusp of M2, anddue to the hypertrophy of this cusp theinterdental space between m2–3 leave a placefor the occlusal closure.

REMARKS: Polydolops unicus is the mostspecialized polydolopine known. This is espe-cially noteworthy in light of the specializationof the entire Polydolopinae, whose morphologyhas diverged considerably from the tribosphe-nic pattern. On the other hand, P. unicus waspreviously unknown from other stratigraphiclevels in Patagonia, and its relative abundancein the Paso del Sapo mammal assemblages issurprising, thus characterizing the faunal asso-ciations. Therefore, P. unicus may be consid-ered as a fossil guide (see below). The onlyknown polydolopine that may be treated as apotential ancestor of the morphology of P.unicus is P. rothi, which shows a derived pat-tern in the molar morphology having: (1) M2with enlarged StD, lingually inclined andcoalescent with the metacone forming a trans-versal axis to the dentary; (2) m2 with thehypoconid anteriorly displaced with conse-quent development of the slightly concavehypocristid. These characters may allow P.unicus and P. rothi to be considered differentgenera, but this hypothesis should be tested inan integrated analysis of the whole family.

Polydolops rothi Simpson, 1936

The holotype of this species is MLP 11–122,a left dentary with p3–m2 from Cerro Pan deAzucar, near Gaiman, Chubut Province, butseveral upper and lower specimens were foundin La Barda and Laguna Frıa. Polydolopsrothi differs from other species of the genus forits poorly to moderately developed p3; sizeintermediate between the larger P. mayoi andthe smaller P. clavulus; m1 with the sharp crestof the trigonid short; hypoconulid clearlymore anterior than the entoconid; M2 slightlyreduced in width with respect to M1; meta-cone and StB well developed and partiallyfused at the base of M2.

Polydolops, sp. nov. 1

LIEB-PV 1153, a maxillary fragment withM1–2, as well as four lower molars areincluded in this new species recovered in LaBarda and Laguna Frıa. It differs fromPolydolops serra, the morphologically closesttaxon, in its smaller size; double StC in M1;accessory labial cusps that form a crenulatecrest; metacone and StD almost fused in M2;the large lingual cusp of m1 the talonid is thesecond posterior to the trigonid (instead of thefirst, as in P. serra). Also, m1 is proportionallylarger and narrower than in P. clavulus,having three labial cusps instead of four, asin P. clavulus. Compared with Polydolops sp.nov. 3 (see below), this taxon is smaller; M1has three cusps in the posterior lobe; there isno ectoflexus; the metacone is well distinct inM2; and m1 has the second lingual cuspundivided and comparatively much larger.


LIEB-PV 1173, a right maxillary fragmentwith M1–2, as well as several maxillary andmandibular remains and isolated teeth havebeen assigned to this new taxon collected inboth localities of Paso del Sapo. In general, itis morphologically closer to the above-de-scribed Polydolops sp. nov. 1 than to any otherknown polydolopine, except for its larger sizeand several other traits including: M1 withtwo lingual cusps instead of three in theposterior lobe; m1 with the second labial cuspdivided and comparatively much smaller;labial accessory cusp larger than in sp nov.2; and hypoconid of m2 more posteriorlyplaced and with the second lingual cuspproportionally smaller. The morphology ofM1—with three cusp rows from which the twolabial ones are merged—is clearly distinguish-able from all other known polydolopines.


LIEB-PV 1178 is a right mandibular frag-ment with p3–m1 from La Barda. This is theonly specimen assigned to this new taxon anddiffers from P. thomasi by having a p2comparatively larger; more significant sizedifference between p3 (larger) and m1 (small-


er); anterior lingual cusp of m1 divided intotwo adjacent cusps. It differs from P. mayoi inits smaller size; p2 with two roots and smallerm1 relative to p3. In general, this new taxonshows a combination of generalized andderived traits.

Genus Amphidolops Ameghino, 1902

Amphidolops, sp. nov. 1

Only three teeth from Laguna Frıa arereferred to this new species: LIEB-PV 1172, aright m2, and two M1s. This is the smallestspecies of the genus Amphidolops and differsfrom A. serrula for a more elongated metaconein M2 and very distinct talonid cusps; M1 isproportionally shorter, with wider stylar shelf;the most posterior labial cusp is the tallest; themetacone in M1 is placed more anteriorly. Itdiffers from Amphidolops sp. nov. 2 (below) inthe presence of only one line of labial cusps inM1, and fewer lingual cusps in m2.

Amphidolops, sp. nov. 2

LIEB-PV 1187, a right m2, and severalisolated lower and upper molars from bothlocalities of Paso del Sapo are referred to thisnew species. With respect to other species ofAmphidolops, it is intermediate in size betweenA. sp. nov. 1 and A. yapa. It differs from A.serrula in its more linear labial side on m2;cusps of lower molars are more distinct;hypoconid of m1–2 is more developed andplaced more anteriorly; and M1 has two cusprows. This new taxon differs from A. sp. nov.1 by having two lines of labial cusps in M1 andmore lingual cusps in m2.

Superorder Xenarthra Cope, 1889

Order Cingulata Illiger, 1811

Family Dasypodidae Gray, 1821

Subfamily Dasypodinae Gray, 1821

Tribe Astegotheriini Ameghino, 1906

Genus Riostegotherium Oliveira andBergqvist, 1998

Riostegotherium, sp. nov.

Figure 5A, B

Several isolated plates of the dorsal carapaceof this new taxon were recovered at La Barda

and Laguna Frıa. These are small dasypodidssimilar in size to the living Dasypus hybridus orD. septencinctus, with very thin osteodermshaving fine punctations on their surface, andcentral figure in the semimovable plates, as seenin R. yanei, from the Itaboraian of Brazil(Oliveira and Bergqvist, 1998). The foraminasurrounding the central figure are placed in anarch, but are fewer than in R. yanei. The centralkeel in the central figure on the exposed surfaceis not well defined. There are few relativelylarge foramina on the posterior margin.

Genus Prostegotherium Ameghino, 1902

Prostegotherium cf. astrifer

Figure 5 C, D

This species has been collected at LagunaFrıa and La Barda. This dasypodid is also ofsmall size, although larger than Astegotherium.Its osteoderms show several punctations sur-rounding the central figure, not placed as anarch as in Riostegotherium, but as an anteriorlypointed ‘‘V’’. The plates have a wrinkled sur-face, but less so than Stegosimpsonia, with thecentral figure subtriangular.

Genus Astegotherium Ameghino, 1902

Astegotherium, sp. nov.

Figure 5E

Several isolated plates from Laguna Frıa areassigned to this new taxon. This small dasypodidis of similar size to the living Dasypus hybridus orD. septencinctus, with very thin and smoothosteoderms, and a lageniform central figure inthe movable scutes, as in A. dichotomus, from theCasamayoran (Vacan, Carlini et al. 2002c); veryfew (or no) foramina surrounding the centralfigure; poorly defined sulcus separating the cen-tral figure from the peripheral ones. The centralkeel of the exposed surface is even less elevatedthan in the Casamayoran species, and has one orrarely two large foramina on the posterior margin.

Genus Stegosimpsonia Vizcaıno, 1994

Stegosimpsonia, sp. nov.

Figure 5F

Also from La Barda and Laguna Frıaare several isolated plates of the dorsal


Fig. 5. Dasypodidae from Laguna Frıa (LF) and La Barda (LB) assemblages. A, scutes ofRiostegotherium sp. nov. from LF; B, scutes of Riostegotherium sp. nov. from LB; C, scutes ofProstegotherium cf. astrifer from LF; D, scutes of Prostegotherium cf. astrifer from LB; E, scutes ofAstegotherium sp. nov. from LF; F, scutes of Stegosimpsonia sp. nov. from LF (also in LB, but not shown).Scale bar 5 10 mm.


carapace of this small dasypodid of similarsize to the living Dasypus hybridus or D.septencinctus. The osteoderms are thicker thanin other astegotheriins from the same locality,with a more wrinkled surface; lageniformcentral figure in the movable plates, as in S.chubutana from the Casamayoran (Barrancansubage, Carlini et al. 2002b), but differs fromthe latter by having fewer and more symmet-rically placed foramina on their surface. Thecentral keel of the exposed surface is betterdefined, with scarce but relatively largeforamina on the posterior margin, having arelatively large one at the junction of aproximal sulcus with the external edge of theplate.

Order Chiroptera

Family indet.

Gen. et sp. nov. 9

Figure 6

Remarkably, two lower bat molars werediscovered in Laguna Frıa, a well-preservedleft m?2 (fig. 6) and a right talonid, bothapparently of the same species (Tejedor et al.,2005). The first appearance of bats in the fossilrecord is in the early Eocene of North America(Jepsen, 1966; Novacek, 1985; 1987; Haber-setzer and Storch, 1989), Europe (Russell etal., 1973), and Australia (Hand et al., 1994).Up to now, the oldest South American recordwas of middle or late Eocene age at SantaRosa locality (Yahuarango Formation) inPeru (Czaplewski and Campbell, 2004; Czap-lewski, 2005).

The Laguna Frıa specimens are identified asbats because of their complete labial cingulumrunning continuously from the anterior baseof the paraconid to the hypoconulid, aprobable synapomorphy in the early stagesof bat evolution (Hand et al., 1994). Themolar cusps are strongly merged into themolar crests rather than being individualized.The trigonid is anteroposteriorly compressed.The paraconid is small and low, much smallerand slightly less lingually situated than themetaconid. The talonid is not strikingly lowerthan the trigonid. The entoconid is moderatein height; it bears a straight entocristid (inocclusal view). The cristid obliqua extendsfrom the hypoconid to a point low on the

posterior wall of the trigonid slightly labial tothe midline of the tooth. The postcristidextends from the hypoconid to a smallhypoconulid (the ‘‘nyctalodont’’ condition)and is separated from the entoconid by asmall groove. The hypoconulid is fully mergedinto the postcristid and is not distinguishableas a separate cusp; it merely forms theposteriorly curving lingual terminus of thepostcristid and is positioned directly posteriorrather than posterolabial to the entoconid.This is a derived condition relative to theprimitive tribosphenic arrangement involvingdistinct talonid cusps (entoconid, hypoconid,and medial or submedial hypoconulid). Theprimitive tribosphenic condition is presentin the archaic bats Ageina, Archaeonycteris,Eppsinycteris, Hassianycteris, Honrovits, Ica-ronycteris, and Necromantis (Simmons andGeisler, 1998; Czaplewski, personal obs.).However, the same configuration of thepostcristid-hypoconulid as in the LagunaFrıa bats is found in other Eocene bats suchas Dizzya (Philisidae), Lapichiropteryx, andStehlinia (Palaeochiropterygidae), and certainextinct or extant representatives of the Em-ballonuridae, Furipteridae, Miniopteridae,Molossidae, Mormoopidae, Natalidae, Phyl-lostominae, some Rhinolophidae, Rhinopo-matidae, and some Vespertilionidae. Althoughthe Laguna Frıa bats probably represent anew species, given the few specimens andcharacters available and their similarity tonumerous extinct and extant bats from severallineages, we are unable to assign the LagunaFrıa specimens to a taxon more circumscribedthan Chiroptera.

Fig. 6. Occlusal view of the Laguna Frıa bat.Scale bar 5 200 mm.


South American Native Ungulates

Order ‘‘Condylarthra’’

Family Didolodontidae (Scott, 1913)

The Family Didolodontidae (Scott, 1913)includes the most primitive South Americanungulates, characterized by a low and buno-dont dentition. They are recorded at severalPatagonian localities in Argentina (Ameghino,1906; Simpson, 1948, 1967a) from the Peligranthrough the Mustersan (Paleocene–?middleEocene), and from the Itaboraian (latePaleocene) of Sao Jose de Itaboraı (Rıo deJaneiro, Brazil) (Paula Couto, 1952).

Gen et. sp. nov. 7

Represented by a left mandibular fragmentwith a well-preserved m3 (LIEB-PV 1611)collected in Laguna Frıa. It is about the size ofthe Protolipternidae, especially Protolipternaellipsodontoides, from the Itaboraian of Brazil(Paula Couto, 1952). The m3 shows a stronglyarcuate paracristid, as in Didolodontidae andprimitive Litopterna (Bonaparte et al., 1993),but its more medial and anterior point seemsto descend to the trigonid basin. The paraco-nid is a conspicuous cusp, anterolabiallyplaced with the base connate to the metaconid.Among the Didolodontidae, the paraconid isalso a distinct cusp, as in the PeligranEscribania chubutensis (Gelfo, 1999, 2004)and the Itaboraian taxa Paulacoutoia proto-cenica and Lamegoia conodonta. In contrast,the paraconid of younger didolodontidsshows a trend toward merging to the metaco-nid, as in the Barrancan subage (late Casama-yoran) Didolodus multicuspis or Ernestoko-kenia, where the paraconid is no longerdistinct. The paraconid is variably present inProtolipternidae, but tends to be almost orcompletely merged to the metaconid. Otherdistinctive characters are the short mesiodistalextension of the talonid; a small cusp locatedat the base and anterior to the entoconid; ashort, cuspate cristid obliqua that connectsthe hypoconid with the labial side of themetaconid; and a transverse, sharp cristidrunning from the entoconid to the posteriorside of the hypoconulid. This peculiar cristiddivides the talonid basin into an anterior,larger portion that opens posterolingually to

the metaconid, and a posterior portion form-ing the basal contact between entoconid andhypoconulid.

Gen. et. sp. nov. 8

Figure 7A

This second taxon is represented by a rightpartial mandible with part of the talonid of m2and complete m3 (LIEB-PV 1612; fig. 7A)also recovered in Laguna Frıa. Even whenheavily worn, the m2 hypoconulid seemscentral and distally placed. This condition issimilar to that of Didolodontidae, where theentoconid and hypoconulid are separated,distinct, and never fused as in someMioclaenidae Kollpaniinae, or close to eachother as seen in some Protolipternidae, such asAsmithwoodwardia. This new taxon clearlydiffers in having the entoconid even largerthan the hypoconid, closing the talonid basin.To a lesser degree, Didolodus and Paulacoutoiaalso show an increase of the entoconid sizeand reduction of the hypoconulid. The ante-rior cingulum is short without labial or lingualexpansions. The trigonid basin of the m3 isshallow and the base of the protoconidcontacts the base of the lingual cusps. Theparaconid is very close and slightly labial tothe metaconid, and connects the protoconidby a short paracristid more transverselyoriented than in the Gen. et. sp. nov. 7. Themetaconid is more distal than the protoconid.The talonid basin is almost completely filledby a huge entoconid, even larger than that ofm2. There is no distal cingulum. The cristidobliqua is short, low, and rounded, andparallels the toothrow.

Order Litopterna (Ameghino, 1989)

Family Protolipternidae (Cifelli, 1983)

This family was recognized by Cifelli(1983a) to contain three small, dentally primi-tive ungulates, basically from the Itaboraianof Brazil. Two of them, Asmithwoodwardiaand Miguelsoria, were previously considereddidolodontids. However, based on reassociat-ed postcranial elements (Cifelli, 1983b), Mig-uelsoria was reallocated in the Protolipter-nidae as a primitive member of the Litopterna,together with Protolipterna. Asmithwoodwar-


Fig. 7. South American native ungulates from Laguna Frıa (LF) and La Barda (LB). A, LIEB-PV 1612,Didolodontidae, gen. et sp. nov., right m2–3; B, Asmithwoodwardia subtrigona, LIEB-PV 1636, left M2; C,Asmithwoodwardia subtrigona, LIEB-PV 1617, right m2; D, Spartnotheriodontidae, Gen. et sp. indet. G,MLP-66-V-12-2, right maxillary fragment with three molariforms (P4–M2?) (LF); E, Henricosbornialophofonta, LIEB-PV 1633, right maxilla with P4–M2 (LB); F, Othnielmarshia lacunifera, LIEB-PV 1618,right maxilla with M1–3 (LF); G, Edvardotrouessartia sola, LIEB-PV 1619; right maxilla with P2–4 (LF); H,Isotemnus sp., LIEB-PV 1646, right maxilla with P4–M3 (LF); I, Isotemnus sp., LIEB-PV 1659, left m2 (LF).Scale bar 5 1 mm.


dia was also included in the Protolipternidaeby Cifelli (1983a) without full explanations(Gelfo and Tejedor, 2004). For the presentpaper, we use Protolipternidae sensu Mc-Kenna and Bell (1997).

Asmithwoodwardia, sp. nov.

Figure 7B, C

This taxon is represented by an m1 or m2(LIEB-PV 1613) from La Barda. It differsfrom Asmithwoodwardia scotti and A. subtri-gona in labiolingual width and in the ar-rangement of the talonid cusps. The hypo-conulid is central and posteriorly placed,while the hypoconulid of A. scotti and A.subtrigona are closer to the entoconid inm1–2. In the trigonid, a small paraconid isappressed against the mesiolabial side of themetaconid.

Asmithwoodwardia subtrigona Ameghino(1901) is represented by several isolated teethfrom Laguna Frıa and a larger sample fromLa Barda (fig. 7B, C). It is a small SouthAmerican ungulate with a bunodont denti-tion and controversial systematic position.Asmithwoodwardia is represented by twospecies: A. scotti, from the Itaboraian ofBrazil (Paula Couto, 1952), and A. subtrigona,from the Vacan subage (Lower CasamayoranSALMA, ?middle Eocene; Cifelli, 1983b) fromPatagonia (Ameghino, 1901; Simpson, 1948).However, McKenna and Bell (1997) suggestedthat Ernestokokenia, a larger Patagonianungulate, is a junior synonym of Asmithwood-wardia (contra Simpson, 1948; Muizon andCifelli, 2000). A. scotti is well represented byisolated teeth and an almost complete skullassociated with the lower jaw. Instead, thetype of A. subtrigona (MACN 10723) consistsof two isolated teeth, an upper and a lowermolar. Simpson (1948) regarded the uppermolar of A. subtrigona as an M2 or possiblyM3, while Paula Couto (1952) suggested thatit was an M1 or M2. The specimens from LaBarda are comparable to A. subtrigona andlead us to confirm that the type specimen is anM3 (Gelfo and Tejedor, 2004). This taxondiffers from A. scotti in its larger size, and inexhibiting conspicuous postparaconular andpremetaconular cristae; the M3 is less trans-versally elongate, and it has a hypocone in

M3. Despite the mentioned differences, thedevelopment of the hypocone of M3s inprimitive bunodont ungulates seems highlyvariable.

Family Sparnotheriodontidae (Soria, 1980b)

The Sparnotheriodontidae are consideredbasal forms of the Order Litopterna (Soria,1980b, 1989, 2001; Hoffstetter and Soria 1986;Lopez, 1999). However, the systematic posi-tion of this family is also controversial. It hasbeen referred to the Order Notoungulata(Soria, 1980a; Marshall et al., 1983), OrderCondylarthra (Cifelli, 1983b; Mones, 1986), orplaced as a subfamily of the Macraucheniidae(McKenna and Bell, 1997).

Gen. et sp. indet. G

Figure 7D

Several specimens clearly referrable to theSparnotheriodontidae were collected inLaguna Frıa, including a right maxillaryfragment (MLP 66-V-12-2; fig. 7D) with threemolariforms (P4–M2?), right M3 (MLP 66-V-12-1), and a broken left M1 or M2 (LIEB-PV1615). These remains are comparable in size toVictorlemoinea labyrinthica Ameghino (1901)with some morphological differences (e.g.,more reduced hypocone in the first molarsand shorter lingual crest of the metaconid)indicating a possible attribution to a differenttaxon, probably related to Notolophus arqui-notiensis Bond et al. (2006).

?Victorlemoinea longidens Ameghino (1901)

An incomplete right lower molariform (p4or m1 LIEB-PV 1614) was collected in LagunaFrıa. This bicrescentic tooth is similar in sizeand morphology to Victorlemoinea longidens.Victorlemoinea labyrinthica and V. longidenswere collected in Vacan levels of Patagonia(Simpson, 1967a). The oldest record of theFamily Sparnotheriodontidae is Victorlemo-inea prototypica Paula Couto (1952), fromthe Itaboraian of Brazil, and its youngestrecord is Phoradiadius divortiensis Simpson etal. (1962) from the Divisaderan of Mendoza,Argentina.


Order Notopterna (Soria, 1984b)

Family ?Amilnedwardsiidae (Soria, 1984a)

This family includes small bunodont ungu-lates with poorly developed ectoloph andparaloph, and a lophoid metaconule. TheCasamayoran genera Amilnedwardsia, Ruti-meyeria, and Ernestohaeckelia, named byAmeghino (1901), were referred by the authorto this family as taxa of generalized morphol-ogy. These genera are almost exclusivelyrepresented by upper molars, with the excep-tion of a lower molariform from theCasamayoran of Canadon Hondo (ChubutProvince), mentioned by Soria (1984b) asreferrable to Amilnedwardsiidae.

Gen. et sp. indet. H

There are two left mandibular fragmentsfrom Laguna Frıa, one with p2 and p3 par-tially broken, and p4–m2 (LIEB-PV 1616),and a second specimen with p3–4 (LIEB-PV1617). They are selenodont and bicrescenticwith the entoconid contacting the hypoconu-lid. Comparison to other lower molariformsmentioned by Soria (1989) indicates that thesespecimens should be regarded as Gen. et sp.indet. members of the Family Amilnedward-siidae. However, given their fragmentarynature and the similarities between theAmilnedwardsiidae and the NotopternaIndaleciidae, they could also be referred tothe latter family.

Order Notoungulata (Roth, 1903)

Family Henricosborniidae (Ameghino, 1901)

This family has several generalized dentalcharacters placing them in a basal positionwith respect to other notoungulates. As G.G.Simpson (1948: 147) said:

The henricosborniids are clearly the most pri-mitive known notoungulates, and they nearlyfulfill all the theoretical requirements for ageneralized type ancestral to all others known.

Traditionally, species referred to this familycharacterize both the Riochican and Vacanfaunal associations.

Henricosbornia lophodonta Ameghino (1901)

Figure 7E

Maxillary and mandibular fragments re-ferred to the Family Henricosborniidae areabundant in both localities of Paso del Sapo,with complete series of premolars and molars,as well as isolated teeth. The presence of astrong metacone, a convex mesostyle area inthe upper molars, and a distinct hypoconulidin m1–2 relate these specimens to Henricos-bornia lophodonta, a typical taxon in severalVacan levels, but also recorded in the upperlevels of the Riochican of Bajo Palangana,Chubut Province. In Paso del Sapo, additionalmandibular fragments are doubtfully assignedto the genus Henricosbornia, morphologicallymore related to H. lophodonta Ameghino(1901) but closer to the size of H. waitehorSimpson (1935a).

Other fragmentary materials with simplerectolophs, a different configuration of themetaloph, and smaller size are here referred ascf. Henricosbornia.

Othnielmarshia lacunifera Ameghino (1901)

Figure 7F

A right maxillary fragment with completeM1–3 (LIEB-PV 1618, fig. 7F) was collectedin Laguna Frıa. These molars have a stronglabial cingulum and a shortened crochet inM1, vestigial in M2, and absent in M3. It isreferred to Othnielmarshia lacunifera. On theother hand, there are several isolated lowermolars with the entoconids clearly separatedfrom the hypoconulids that may be alsoattributable to this species. The type of O.lacunifera comes from ‘‘west of Rıo Chico’’,and thus is Vacan in age (Simpson, 1967a) andSimpson himself collected materials inCanadon Vaca.

Family Notostylopidae (Ameghino, 1897)

Notostylopids acquired a specialized, styli-form incisors and diastema during their earlystages of their evolution, giving them arodentlike appearance. In Patagonia, thisfamily is known from the Riochican throughthe Mustersan, but the latest representativeswere collected in the Tinguirirican of central


Chile (referred to the late Eocene–earlyOligocene by Flynn et al., 2003). They werenever diverse but were the most abundantungulates during the Vacan and Barrancansubages. Three genera are described for thePaso del Sapo localities below.

Edvardotrouessartia sola Ameghino (1901)

Figure 7G

Two maxillary fragments were collected atLaguna Frıa, one with broken P2–4 (LIEB-PV1619; fig. 7G), and the other with incompleteP4 (LIEB-PV 1620). The premolars show aflat paracone and, in labial view, the charac-teristic pyramidal shape of Edvardotroues-sartia sola. Specimens of E. sola came from‘‘west of Rıo Chico’’ (Simpson, 1967a, b), andthere are excellent collections also fromCanadon Vaca in the Museo de La Plataand Museo de Mar del Plata. Thus until now,E. sola was exclusive to the Vacan.

Homalostylops parvus Ameghino (1897)

A mandibular fragment with m1–2 of asmall notostylopid was collected in La Barda(LIEB-PV 1621). By its size and the presenceof an accessory cusp in the middle of themetalophid, it is certainly referred toHomalostylops parvus, one of the few speciesrecorded for both the Vacan and Barrancansubages. A left mandibular fragment with m2(LIEB-PV 1622), also collected in La Barda, isreferable to this species.

Notostylops sp.

Mandibular fragments and isolated upperteeth that can be referred to the genusNotostylops are abundant in both localitiesof Paso del Sapo. However, their specificattribution is difficult. Notostylops has beenfound in the upper levels of the Riochican (i.e.,in the Ernestokokenia chaishoer faunal zone),and in the Casamayoran sensu lato (Vacanand Barrancan subages).

It is important to note that, although thelower molars of Notostylops and Homalo-stylops are very similar morphologically, thereis a significant difference in size.

Family Oldfieldthomasiidae (Simpson, 1945)

This family includes small- to moderate-sizedungulates with a generalized crown morpholo-gy, thus being basal with respect to theTypotheria-Hegetotheria radicle. The oldestoldfieldthomasiids are from the Itaboraian ofBrazil and Patagonia (Pascual and Ortız Jaure-guizar, 1992), and one of its taxa, KibenikhoriaSimpson (1935a), characterizes the middlelevels of the Riochican (‘‘Kibenikhoria faunalzone’’; see Simpson, 1935b). The youngestrecord of this family is from the Fray BentosFormation in Uruguay (Ubilla et al., 1999).

Gen. et. sp. indet. I

Some mandibular fragments collected inLaguna Frıa show simple molars with opentrigonids, transversely crestlike entoconid, notfully fused to the hypolophid and separatedfrom the metaconid by a deep sulcus. Thismorphology is certainly related to theOldfieldthomasiidae. The diagnostic charactersfor the oldfieldthomasiid species are generallyfor the upper molariforms; therefore, theselower materials are here described as Gen. et.sp. indet. However, the general morphology,crown height, and size closely approximate thegenus Kibenikhoria (e.g., LIEB-PV 1658).

Family Archaeopithecidae (Ameghino, 1897)

This family includes small, generalized no-toungulates with relatively high-crowned molars,recorded from the ‘‘Ernestokokenia chaishoerfaunal zone’’, (Upper Riochican; see Simpson,1935b) and they were relatively abundant up toMustersan levels (Cladera et al., 2004).

Archaeopithecus cf. A. rogeri Ameghino (1897)

Several maxillary and mandibular fragments(e.g., LIEB-PV 1625 to 1628), as well as isolatedteeth (e.g., LIEB-PV 1629) referred to thisfamily have been found in La Barda andLaguna Frıa. The Archaeopithecidae is basedon Archaeopithecus rogeri Ameghino (1897), ofunclear stratigraphic provenance, probablyBarrancan, and Acropithecus rigidus Ameghino(1901), from Canadon Vaca (Vacan). Based on


the morphology of the ectoloph and for thepresence of a strong anterolingual cingulum inthe premolars, the materials collected at thePaso del Sapo localities are closely related toArchaeopithecus rogeri, but the species assign-ment is still uncertain.

Family Interatheridae (Ameghino, 1897)

Subfamily Notopithecinae (Simpson, 1945)

This subfamily includes the oldest and moregeneralized members of the Interatheriidae butsince this grouping is mainly recognized on thebasis of plesiomorphic characters, its taxonom-ic status is debated. The notopithecines aretypotheres of small size, probably browsersand, in part, ecologically equivalent to themembers of the families Oldfieldthomasiidaeand Archaeopithecidae. Some Notopihecinae(e.g., Notopithecus) show craniodental andpostcranial characters convergent with thosefound in lemuriform primates from the earlyTertiary of the Northern Hemisphere, thusexplaining why Ameghino characterized thisgroup as ‘‘southern monkeys’’.

The Notopithecinae appeared in the fossilrecord in the uppermost levels of the Riochicanfrom Bajo Palangana, eastern Chubut province(Simpson, 1967b), and its youngest record camefrom the Tinguirirican of central Chile (Flynn etal., 2003). Among the Eocene faunal associa-tions of Patagonia, the notopithecines areabundant with five genera recognized: Notopi-thecus Ameghino (1897), for the Riochican andCasamayoran of Patagonia, and with somedoubts for the Eocene of Bolivia; AntepithecusAmeghino (1901) and Transpithecus Ameghino(1901) from the Casamayoran (s.l.) of Pata-gonia; Guiliermoscottia Ameghino (1901) fromthe Mustersan of Patagonia; and PunapithecusLopez and Bond (1995) from levels referred tothe Mustersan in Catamarca, northwesternArgentina.

Gen. et sp. indet. J

A few isolated teeth that may be attribut-able to the Notopithecinae were collected atLaguna Frıa. Some of these are probablyrelated to the genus Notopithecus (e.g., LIEB-PV 1655, an isolated lower p3) but a broadersystematic revision is needed.

Family Isotemnidae (Ameghino, 1897)

The Isotemnidae are moderate to largeungulates characterized by having large ca-nines and a generalized molar pattern for theToxodontia. This family is represented bynumerous maxillary and mandibular frag-ments and isolated teeth in both localities ofPaso del Sapo.

Isotemnus sp. Ameghino (1897)

Figure 7H, I

There are two specimens, a left maxilla withP4–M3, slightly worn (LIEB-PV 1647) and aright maxilla also with P4-M3 (LIEB-PV 1646;fig. 7h, i), with transverse molars, well-devel-oped, columnar metacone and lingual cingu-lum absent. These traits characterize Isote-mnus and clearly differ from PleurostylodonAmeghino (1897). Also, there are severalmandibular fragments (LIEB-PV 1650 to1653) referred to the genus Isotemnus, basedon the structure of the metaconid, which is notoriented posteriorly and thus the talonid basinis open. The lower molars have better devel-oped lophids than Isotemnus ctalego fromCanadon Hondo (Itaboraian) and Isotemnussp. from the Ernestokokenia chaishoer zone ofBajo Palangana. This is indicative of a post-Riochican evolutionary stage. In Patagonia,the genus Isotemnus is also recorded inRiochican and Vacan levels.

Order Astrapotheria (Lydekker, 1894)

Family indet.

Gen. et sp. indet. K

A left m1 or m2 (LIEB-PV 1623) recoveredat Laguna Frıa is attributed to theAstrapotheria. However, the family attributionis difficult because the morphology resemblesthat in the genus Trigonostylops Ameghino(1901) (Astrapotheria, Trigonostylopidae) aswell as that in Tetragonostylops Price and PaulaCouto (1950) (Astrapotheria, Astrapotheri-idae). Both genera can be recognized bytheir upper molariforms, but the lowers lackdiagnostic characteristics. The species ofTrigonostylops are known from the Riochicanthrough the Mustersan of Patagonia, while


Tetragonostylops comes from the Itaboraian ofBrazil and Vacan of Argentina.

Order ? Astrapotheria

Gen. et sp. indet. L

Among the materials from Laguna Frıa,there is a right maxillary fragment with part ofthe hypertrophied and compressed canine thatmay be attributable to the Astrapotheria(LIEB-PV 1624), but its more precise attribu-tion is doubtful. We are unable to refer thisspecimen to any other South American orderof ungulates.

DISCUSSION

MARSUPIALS

The mammalian fauna of Paso del Sapoincludes nearly 30 species from several mar-supial orders, of which about 19 species arenew or probably new. These marsupials areclosely related to those from older SALMAs,such as the Itaboraian and Riochican (12species); none of these species are present insediments younger than those from Paso delSapo.

Marsupials are the most abundant mam-mals from Paso del Sapo, and are representedby almost all the South American marsupialorders. Among them, the diversity and rich-ness of the Polydolopinae is remarkable,comprising not only the richest polydolopinefauna from Patagonia but the richest in SouthAmerica to date. It is noteworthy that severalmarsupials had frugivorous adaptations (i.e.,polydolopines and caroloameghiniids), andthis may be related to the diversification ofplants, as indicated for the record of 102 leafspecies in the nearby early Eocene caldera lakedeposits of Laguna del Hunco (Wilf et al.,2003, 2005), as well as the Eocene paleoflorafrom Rıo Pichileufu (Berry, 1938; Petersen,1946; see also Wilf et al., 2003), located about160 km NNW of Laguna del Hunco, thatcontains several of the same species as Lagunadel Hunco.

XENARTHRANS

Due to the manner of collecting (mostlyscreening and washing), all specimens are

isolated, but it appears that a large number ofspecimens are represented. All of the osteo-derms are from members of the Tribe Astego-theriini, the most primitive among dasypodids(Carlini et al., 2002a). Consequently, theabsence of Euphractinae is remarkable bycomparison with their abundance in theBarrancan subage (upper Casamayoran) fromGran Barranca, Chubut (Meteutatus and espe-cially Utaetus). The faunal differences are alsoremarkable with respect to the Vacan subage,where the first Euphractinae are recorded,together with a lower diversity of Astego-theriini with more advanced taxa. These dif-ferences with respect to the Casamayoranfaunas (Carlini et al., 2002b, 2002c), as well asthe presence of a new species of Riostego-therium (a genus until now only present in theItaboraian of Brazil) and, with the youngestrecord in Paso del Sapo, a new species ofStegosimpsonia and another new species ofAstegotherium, all of which are more primitivethan the Casamayoran species, certainly sug-gests an older age for the sediments of LagunaFrıa and La Barda (Carlini et al., 2002a). Inaddition, the diversity of Astegotheriini indi-cates a warmer and more humid paleoenviron-ment than that inferred for the Casamayoran.At this time, the species from Laguna Frıa andthose from the Vacan (Carlini et al., 2002c)include the greatest diversity of Astegotheriini.

BATS

As mentioned above, we are unable toassign the Laguna Frıa bat specimens to anyrank other than Chiroptera. However, judgingfrom the observable morphology, its size andlower molar features indicate insectivorousfeeding habits. In this respect, it is noteworthythat the Laguna Frıa mammal assemblage isprobably contemporary with the very richearly Eocene Laguna del Hunco flora (Wilf etal., 2003), which suggests the early radiationof modern angiosperm lineages in Patagoniaas well as their insect pollinators, which couldhave served as food for the bats.

UNGULATES

There are no significant differences intaxonomic composition and ecological roles


among the ungulates from Laguna Frıa andLa Barda. In general, they are characterizedby the dominance of small to moderate sizeanimals, with brachydont, bunodont to loph-odont dentitions. Despite the above-men-tioned differences regarding minor morpho-logical details, the Didolodontidae andProtolipternidae include the smallest ungu-lates from Paso del Sapo. The most conspic-uous taxon is Asmithwoodwardia subtrigona,recovered in both localities but more abun-dant at La Barda. The latter locality has alow taxon diversity of Didolodontidae andProtolipternidae but a high minimum numberof individuals.

Along with Asmithwoodwardia, the Dido-lodontidae from Laguna Frıa are representedby larger taxa, probably two new genera andspecies (here named Gen. et sp. nov. 1 and Gen.et sp. nov. 2). These are larger when comparedparticularly with Asmithwodwardia; in contrast,they are smaller than any other knownDidolodontidae (e.g., Escribania chubutensis,from the Peligran, or Didolodus multicuspis,from the Barrancan subage). This increase insize, along with particular characters, such asthe transverse and sharp cristid running fromthe entoconid to the posterior side of thehypoconulid in Gen. et sp. nov. 7 or the largerentoconid closing the talonid basin in Gen. etsp. nov. 8, could be related to a wide spectrumof adaptive strategies. However, it is necessaryto test the possible intra- or interspecificvariability within these samples.

Small bunodont ungulates are well repre-sented in both faunas from Paso del Sapo. Incontrast, the absence of some taxa common inthe South American Paleogene is remarkable,such as the larger Didolodontidae and Proto-lipternidae. One is the poorly known Ernesto-kokenia, morphologically similar to Asmith-woodwardia but larger in size, found in differentPatagonian localities from the Riochicanthrough the Casamayoran. Simpson (1935b)divided the Rıo Chico Formation into threefaunal zones, from older to younger: Carodnia,Kibenikhoria, and Ernestokokenia chaishoer,the latter characterized by E. chaishoer butalso E. yirunhor, recovered in the Kibenikhoriazone as well. The absence of Ernestokokeniain the Paso del Sapo assemblage deservesmore attention. There is no record of either

Escribania chubutensis, from the PeligranSALMA, or any species of Didolodus, wellrepresented in the Casamayoran. This isinteresting because the presence of primitivebunodont ungulates is usually characterized bya broad size range, as for example in theItaboraian. To summarize, the size range in theRiochican and Casamayoran Didolodontidae,not seen in Paso del Sapo, may be due to localtaphonomic and/or paleoecological conditionsinstead of temporal differences.

The most significant and best representedbunodont ungulate from Paso del Sapo isAsmithwoodwardia subtrigona, also recordedin the Vacan subage. As mentioned above, themore primitive Asmithwoodwardia scotti isknown from the Itaboraian of Brazil.Therefore, judging from the Didolodontidaeand Protolipternidae, an age ranging from thepost-Itaborian through Vacan can be inferredfor the Paso del Sapo fauna.

The two members of the Sparnotherio-dontidae reported herein were recovered onlyfrom Laguna Frıa and are comparable toVictorlemoinea labyrinthica and ?Victorle-moinea longidens. Both species came from‘‘west of Rıo Chico’’, which most probablybelongs to a Canadon Vaca locality (Vacan).Victorlemoinea is also represented in theItaboraian by V. prototypica, and in theErnestokokenia faunal zone of the Riochicanby an m3 from the Feruglio collection (nu 13)(Simpson, 1935a, 1948). The sparnotheriodon-tids here considered Gen. et sp. indet. appearmore advanced than the primitive Victorle-moinea prototypica, and more similar in size toV. labyrinthica. In contrast, the new specimensshow intermediate character states comparedwith Notolophus arquinotiensis from theAntarctic Peninsula (Bond et. al., 2006). Forexample, Victorlemoinea labyrinthica has astrong crest between the metaconule and theprotocone, shorter in MLP 66-v-12-2 fromPaso del Sapo, and absent in the Antarcticform. Even though sparnotheriodontids show abroad temporal and latitudinal range (from theItaboraian of Brazil through the Divisaderan ofMendoza, Argentina), the similarities to theVictorlemoinea species from Patagonia relatethe Paso del Sapo taxa to the Vacan forms.

Among the Notoungulata, the Henri-cosborniidae and Notostylopidae are common


in both localities described in this paper. Thefirst family includes two genera, Henricos-bornia and Othnielmarshia, that are probablypresent in the ‘‘Ernestokokenia chaishoerfaunal zone’’, the youngest levels of theRiochican SALMA (Simpson, 1935a, 1935b;Bond et. al., 1995), and certainly in the Vacan(Simpson, 1948). The Scarritt Collection(Simpson, 1948, 1967a, b) includes severalspecimens of Othnielmarshia lacunifera, fromCanadon Vaca. However, the precise strati-graphic provenance for the type is unknown.It came from ‘‘west of Rıo Chico’’ (Ameghino,1901), probably from the Upper Rıo Chico orfrom the coarser tuffs of the Vacan (Simpson,1948). Henricosbornia waitehor, similar to H.lophodonta based on the lower dentition,with narrower molars, was described forthe Kibenikhoria zone (middle Riochican)(Simpson, 1935a, 1935b).

One of the most conspicuous members of themammalian fauna from the late Riochican(Ernestokokenia chaishoer faunal zone) to thelate Casamayoran (Barrancan) was the notos-tylopid Notostylops sp. Both localities of Pasodel Sapo have produced several specimens ofNotostylops with no specific attribution for thereasons mentioned above. Besides the commonNotostylops sp., the presence of Homalostylopsparvus in La Barda, and Edvardotrouessartiasola in Laguna Frıa, previously known for allof the Casamayoran and from the Vacan,respectively (Simpson, 1948), are most impor-tant in estimating the age of this fauna.Edvardotrouessartia seems to be even morevaluable, not only for its restricted Vacandistribution, but also because the charactersthat distinguish Homalostylops from Noto-stylops seem to be ambiguous. FollowingSimpson (1948), almost all characters shownby Homalostylops parvus closely resemble thoseof Notostylops, except for its smaller size; thus,Simpson retained the genera with doubts basedon the holotype differences.

The isotemnids recorded in Paso del Sapoexhibit a high degree of lophodonty, reminis-cent of species such as Isotemnus primitivus orAnisotemnus distentus, both from the Vacansubage (Simpson, 1967b).

The Archaeopithecidae, also well represent-ed in both localities of Paso del Sapo, are herereferred as Archaeopithecus cf. rogeri. This

taxon does not provide much information andthe taxonomy of the whole family needs athorough revision. Moreover, the type of A.rogeri (MACN 10816) has no precise localityinformation although it probably came fromthe south of Colhue-Huapi, as well as othersynonymous species, thus being of Casa-mayoran age (Simpson, 1967b).

NEW SALMA FOR THE PALEOGENE OF

SOUTH AMERICA?

Based on both the Laguna Frıa LocalFauna and the La Barda Local Fauna,composed of a remarkable diversity andabundance of mammals, many of thempreviously unknown or with morphologicalnovelties, we suggest that these assemblagesmay represent a new Paleogene SALMA.Also, the apparent correlation with the LaMeseta Fauna of the Antarctic Peninsula isdiscussed. We estimate the age of the Paso delSapo units as between 49.5 Ma and 45 Ma.They therefore fill a faunal gap between theCasamayoran and Riochican SALMAs.

A data matrix of 118 genera and eightfaunas/SALMAs, was built for a quantitativeanalyses (table 1, fig. 8). Data were obtainedfrom the literature (Bond et al., 1995; Pascual etal., 1996) and personal observations. Mammalassemblages include the Paso del Sapo fauna,the Carodnia zone, and the Tiupampan, Peli-gran, Itaboraian, Riochican, and CasamayoranSALMAs. As mentioned above, the Casama-yoran SALMA was divided into Vacan andBarrancan subages. The temporal distributionof taxa in each fauna/SALMA was scored aspresence (1) or absence (0) in the data matrix.Pseudo-extinctions were not coded in thematrix. The cluster analysis was performedwith NTSYS 2.0 software (Rohlf, 1997) usingthe Jaccard coefficient, and the unweightedpair-group method using arithmetic averages(UPGM). Because of that, only the presence oftaxa between faunas was considered to establishsimilarity between them, avoiding the sharedabsences, as a similarity criterion (Cheetmanand Hazel, 1969). The Cophenetic CorrelationCoefficient (CCC, Sneath and Sokal, 1973) wascomputed for the resulting phenogram.

The results of the cluster analysis (CCC:0.93638) shows a principal group formed by


the (Peligran (Itaborian ( (Riochican – Pasodel Sapo) (Vacan – Barrancan) ) ), leaving theCarodnia Zone with a low similarity value tothis group, external to it, and the Tiupampanwith no relation with the rest of the cluster(coefficient 0.00) (fig. 8). The Carodnia zonevalue could be biased due to the low diversityof taxa found in this association, and thecommon presence of the genus Carodnia (butdifferent species) with the Itaboraian. The lackof similarity of the Tiupampan with respect toother SALMAs reflects the immigrant natureof the taxa therein, which are more related tothose of the North American Puercan LandMammal Age, than to those of the Paleogeneof South America. The Casamayoransubages—Vacan and Barrancan—show thehighest similarity in the analysis. The Pasodel Sapo fauna is more closely related to theRiochican than to any other SALMA.

The Paso del Sapo mammalian fauna willbe defined by the first occurrence ofPolydolops unicus, sp. nov. This species isextremely abundant both at Laguna Frıa andLa Barda, showing an unusual, very distinctdental morphology.

Also, this fauna is characterized (table 1) bythe presence of Astegotherium, Riostegotherium,Stegosimpsonia, Eomicrobiotherium, Pauladel-phys, Edvardtrouessartia, Homalostylops, Othni-elmarshia, Peradectidae new genus 1, Caroloa-meghiniidae new genus 2, Peradectoidea newgenus 3, Paucituberculata new genus 4,

Hathliacynidae new genus 5, Didolodontidaenew genus 7, Didolodontidae new genus 8,Chiroptera new genus 9.

Taxa that last occur in Paso del Sapo are allmarsupials and include: Gashternia, Itaborai-delphys, Marmosopsis, Nemolestes, Palangan-ia, Protodidelphis. Taxa that also occur inearlier and later SALMAs are Amphidolops,Derorhynchus, Polydolops, Archaeopithecus,Asmithwoodwardia, Henricosbornia, Isotem-nus, Notostylops. Additionally, taxa unknownin Paso del Sapo but that occur in earlier andlater SALMAs are Eohyrax, Ernestokokenia,Maxschlosseria, Notopithecus, Oldfieldthoma-sia, Tetragonstylops, Trigonostylops, Victorle-moinea.

MEASURED SECTION

The outcrops of the Laguna Frıa LocalFauna are located in the Estancia San Ramonfarm, property of Mr. Rafael Nicoletti, about170 km northeast of the city of Esquel, and28 km west of Paso del Sapo (figs. 1, 9, 10).Figure 9 presents a measured section ofLaguna Frıa. The fossiliferous interval of theLaguna Frıa tuffaceous sediments (likelycorrelative of the Tufolitas Laguna delHunco Formation exposed within the SierraHuancache Caldera) is about 60 meters thick.The top of the stratigraphic unit is obscuredby alluvium. The Laguna Frıa sediments restunconformably on a ?rhyolitic tuff, about 2 m

Fig. 8. Results of the cluster analysis using data matrix of 118 genera and eight faunas/SALMAsdescribed in table 1.


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thick, that in turn lies conformably on anignimbrite dated at 49.51 6 0.32 Ma asdescribed above. Regional correlation indi-cates that the Laguna Frıa Tuffs are uncon-formably overlain by the upper member of theAndesitas Huancache (fig. 2). The unconfor-mity shown at the base of the Laguna FrıaTuffs is likely of only short duration in thatthe tuffaceous basal sediments there likelyrepresent a continuation of the volcanic eventfrom which the ignimbrite was erupted.

ESTIMATED AGE

As indicated above a 49.51 6 0.32 Maignimbrite immediately underlies the mam-mal-bearing tuffs of the Laguna Frıa locality(figs. 2, 9). This gives a maximum age for thebase of the Paso del Sapo fauna. Overlying themammal-bearing levels at Laguna Frıa is abasalt dated at 47.89 Ma 6 1.21 Ma (Gosseset al., 2006, samples 2 and 3). In turn, themammal-bearing tuffs at La Barda are depos-ited above the 47.89 6 1.21 Ma basalt, and areinterbedded with the Andesitas Huancachelava flows. To the west, the AndesitasHuancache deposits have yielded three K/Ardates near 43 Ma (Mazzoni et al., 1991). TheLa Barda Tuffs underlie the 43 Ma lava flowsof the AH (fig. 2). This gives a maximum timespan for the Paso del Sapo fauna of 49.5–43 Ma. Several lines of reasonings suggest thatthe actual range is even narrower time: (1) Asmentioned below, the Paso del Sapo mammalssuggest an older age than those of the Vacansubage; the Vacan was tentatively considered(Carlini et al., 2005: fig. 1) as representing atime interval of ca. 44–45 Ma. (2) The faunalsimilarities between the Laguna Frıa and LaBarda assemblages suggest that deposition ofthe mammal-bearing tuffs at both localitiesrepresented a relatively short time span. (3) Asdiscussed below, the Laguna Frıa and the LaBarda mammals share several significant taxawith the mammalian association collected atTELM 5 (or Cucullaea 1 Allomember) of theLa Meseta Formation in the AntarcticPeninsula. Numerical ages for TELM 5 levelsbased on Strontium isotopic determinationsare between 49 and 51 Ma (Ivany, 2007).Summarizing, we preliminarily conclude thatthe best estimate for the time span of the Paso

del Sapo fauna as a possible new biochrono-logical unit including the La Meseta fauna isbetween 49.5 Ma and 45 Ma.

RELATION TO OTHER SALMAS: Kay et al.(1999) recently revised the age of the Barran-can subage (late Casamayoran SALMA) toabout 39 Ma (Carlini et al., 2005; Madden etal., 2005). This also resulted in an upwardrevision of the correlation of the MustersanSALMA to latest Eocene (ca. 36 Ma). Prior tothe work of Kay et al. (1999), the Casa-mayoran SALMA had been conventionallyconsidered as early Eocene, and the Mustersanas late Eocene. Considering the revisionsstemming from Kay et al. (1999) and thosepresented by Carlini et al. (2005) that give anestimation of 44–45 Ma for the Vacan, mainlybased on the faunas, and the precedingRiochican SALMA with an estimated age ofno younger than 55 Ma (Pascual and OrtızJaureguizar, 1991) thus left a gap in the earlyto medial Eocene record in the SouthAmerican mammal age sequence. Recogni-tion of the Paso del Sapo mammalian faunanow fills part of that gap.

RELATIONS WITHIN THE PASO DEL SAPO

MAMMALIAN FAUNA

The La Barda Local Fauna contains taxathat pertain to the same genera as found in theLaguna Frıa Local Fauna, but are representedby different species, compatible with theabove-discussed differences in radioisotopicage of the two local faunas. The onlyrecognized correlative of these two Paso delSapo assemblages is the fauna from the LaMeseta Formation of the Antarctic Peninsula(Vizcaıno et al., 1998). This correlation isbased on the La Meseta Fauna sharing taxaexclusively with the Laguna Frıa, includingthe didelphimorphian Pauladelphys and alitoptern related to Notolophus, among othertaxa such as Polydolops and Derorhynchus, thelatter also found elswhere in Patagonia. Taxapresent in La Meseta but not in Laguna Frıainclude the gondwanathere Sudamerica sp. Atthe moment this is considered a likely paleo-geographic restriction of a possible gondwa-nan inhabitant from more western localities inArgentina, or a currently unfilled samplingbias in the Argentine Paso del Sapo sites. The


Antarctic connection may have been differentand more favorable for the western biotas ofPatagonia in contrast to those from easternand central Patagonia, thus suggesting apaleobiogeographic relationship between thePaso del Sapo fauna from northwesternChubut and the Antarctic Peninsula. TheWeddelian Biogeographic Province proposedby Zinsmeister (1979, 1982) based on marineinvertebrates appears reflected also by themammals and to have a continental extensioninto South America. To reinforce theAntarctic connections of the Paso del Sapo

fauna, new strontium isotopic ages for Telm 5(Cucullaea I and Cucullaea II allomembers) inthe La Meseta Formation, where the mam-mals were collected, are of 49–51 Ma (Ivany,2007), thus closely correlated with the LagunaFrıa assemblage.

Neither the Laguna Frıa nor La Barda localfaunas contain Maclydotherium, Adiantoides,Anisotemnus, Carolozitellia, Didolodus, Enneo-conus, Ernestohaeckelia, Florentinoameghinia,Peripantostylops, Pleurostylodon, Scaglia, orThomashuxleya, taxa considered characteristicof the Vacan sub-SALMA (table 1).

Fig. 9. Measured section in the type area of the Laguna Frıa Fauna, about 500 meters northeast of thetype locality.


Fig. 10. Top: General view of the measured area shown in figure 9. LF: fossiliferous levels; I: underlyingignimbrite dated in 49.51 6 6 0.32 Ma; AH: Andesitas Huancache, overlying basalts dated in 47.89 6 6 1.21Ma. Bottom: Partial exposures of the Laguna Frıa (LF) section and the Barda Colorada ignimbrite (IBC);between both levels is the ignimbrite mentioned above (I), underlying Laguna Frıa.


A third possible area where the Paso delSapo levels may be represented is the Gaimanregion (fig. 1, #10), where Simpson (1935a)described a pink sandstone level at the base ofthe Cerro Pan de Azucar profile, which hasyielded so far only three mammalian taxa:Polydolops rothi, Protodidelphis sp., andIsotemnus ctalego. (1) It is noteworthy thatP. rothi occurs only at this locality and at Pasodel Sapo local faunas. (2) Though representedby very scarce remains, both the La Bardalarger specimen of Protodidelphis and thatfrom Gaiman are very similar, probablyconspecific (they are the largest knownspecies of Protodidelphis); (3) Isotemnus ctale-go comes from Cerro Pan de Azucar andalso the Itaboraian of Canadon Hondo (i.e.,Kibenikhoria faunal zone), Chubut.

CLIMATIC SETTING

Wilf et al. (2003, 2005) indicate that Lagunadel Hunco flora, recovered from the SierraHuancache Caldera located 20 km northwestof Laguna Frıa, lived in a subtropical climatewith moderate seasonality. The Laguna delHunco flora was recovered from the TufolitasLaguna Hunco Formation, dated at 52–54 Ma. The Pichileufu Flora, from the vicinityof Bariloche, Patagonia, is of about 47 Ma inage and reflects a similar climatic setting, eventhough located about 300 km northwest ofLaguna Frıa. On this basis it appears that thePaso del Sapo mammals lived under theconditions indicated by these floras.

We also note that the radioisotopic age ofthe Laguna del Hunco flora is close to thatestimated for the faunas from Laguna Frıaand La Barda (Wilf et al., 2003), at the time ofthe early Eocene climatic optimum. As aresponse to this short period of warm andequable climate in middle latitudes on bothhemispheres, the diversification of plants andanimals in central-western Patagonia, is re-flected in the rich fauna and flora from Pasodel Sapo. Thus, the Laguna del Hunco flora isan outstanding complement to the dataprovided by the abundant and diverse mam-mals from Laguna Frıa and La Barda.

This paleoflora includes taxa that areextinct today in South America, but somerelatives are still present in Australasia, thus

reinforcing the persistence and potentialimportance of the Weddelian BiogeographicProvince (sensu Zinsmeister, 1979, 1982)as a biogeographic connection for westernPatagonia’s biotas. It is possible that some ofthe Paso del Sapo mammals reflect geograph-ic, temporal, and phylogenetic relationshipswith those from the Eocene of the AntarcticPeninsula, such as the derorhynchid marsupi-als and sparnotheriodontid litopterns fromLaguna Frıa, with strong affinities with theAntarctic forms. In sum, the taxonomic andpotential biogeographic relations betweenPaso del Sapo and Eocene fauna fromAntarctica lead us to support affinities alsoas a biochronological unit.

The mammals from Laguna Frıa mayreflect a relatively short period of volcanicquiescence after the ignimbritic event of BardaColorada, followed by a basaltic event of theHuancache andesites. It is possible that agradual change occurred in the environment,but not a rapid local extinction triggered bythe Huancache event. These later andesiteswere lava flows instead of ignimbritic explo-sions, thus having a less catastrophic effect ata regional scale compared with the BardaColorada ignimbrite.

ACKNOWLEDGMENTS

A special thanks to Mrs. ‘‘Coca’’ SanMartın and Mr. Rafael Nicolletti for allowingus to work in Estancia San Ramon (LagunaFrıa), as well as to the Grenier family whoallowed us to work in their land, Estancia 26de Mayo (La Barda). We are also grateful toour collaborators in the field and the labora-tory: Ariel Humai, Claudia Tambussi, Con-stanza Koefoed, Viviana Albarracın, MarıaLuisa Pemberton, Leonardo Avilla, and ErikaAbrantes. Marcela Tomeo improved Figure 1,3, and 4.

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