Two New Taxa (Caviomorpha, Rodentia) from the Early Oligocene Tinguiririca Fauna (Chile)

Copyright © American Museum of Natural History 2012 ISSN 0003-0082 AMERICAN MUSEUM NOVITATES Number 3750, 36 pp. July 20, 2012 Two New Taxa (Caviomorpha, Rodentia) from the Early Oligocene Tinguiririca Fauna (Chile) ORNELLA C. BERTRAND,1 JOHN J. FLYNN,2 DARIN A. CROFT,3 AND ANDRE R. WYSS4 ABSTRACT Here we describe two new caviomorphs from the early Oligocene Tinguiririca Fauna of the Andean Main Range of central Chile, representing the most ancient rodents known from the mid to high latitudes of South America, and the second-oldest securely dated rodents from the continent. These two new taxa are each documented by single partial mandibles bearing largely complete dentitions. Representing two new taxa, Andemys termasi, gen. et sp. nov., and Eoviscaccia frassinettii, sp. nov., these caviomorphs are informally referred to the pan-Dasyproctidae and pan-Chinchillidae, respectively. These taxa, together with recent findings in Peru, confirm that caviomorphs were well diversified prior to the Deseadan SALMA, that they likely originated during the middle to late Eocene, but that they did not spread from the tropics until some time after the Mustersan—a well-sampled interval from which rodents are unknown in higher latitudes. Additionally, in documenting the earliest occurrence of hypsodonty among caviomorphs Eoviscaccia frassinettii, sp. nov., provides important insights into the acquisition of this common mammalian dental innovation in rodents. 1 Laboratoire de Paléontologie, Institut des Sciences de l’Évolution, c.c. 64, Université Montpellier II, Place Eugène Bataillon, F-34095 Montpellier cedex 05, France; and Kade Fellow, Richard Gilder Graduate School, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024. 2 Division of Paleontology and Richard Gilder Graduate School, American Museum of Natural History. 3 Department of Anatomy, Case Western Reserve University, Cleveland, OH 44106. 4 Department of Earth Science, University of California, Santa Barbara, CA 93106. 2 AMERICAN MUSEUM NOvITATES NO. 3750 INTRODUCTION The early Oligocene Tinguiririca Fauna from the Andean main range of central Chile includes two new rodent taxa, both represented by partial mandibles (Flynn et al., 2003). We describe and name these taxa in this report. The sudden mid-Cenozoic appearance of caviomorphs in South America’s stratigraphic record is perplexing, given the continent’s geographic isolation at the time and the “AfricanAsian” distribution of the group’s nearest putative relatives, Phiomyidae and Baluchimyinae (Marivaux et al., 2000, 2002; Jaeger et al., 2010). The venerable notion of caviomorph monophyly (Wood and Patterson, 1959) has been corroborated repeatedly by molecular analyses (Nedbal et al., 1994; Huchon and Douzery, 2001; Opazo, 2005; Farwick et al., 2006; Poux et al., 2006; Huchon et al., 2007; Blanga-Kanfi et al., 2009; Churakov et al., 2010), but morphological evidence has remained more ambiguous. Auditory (Meng, 1990) and dental (Marivaux et al., 2004; Sallam et al., 2009) features have been interpreted as indicative of caviomorph monophyly, as has a recent combined molecular and morphological dataset (Horovitz et al., 2006). Nevertheless, a polyphyletic origin involving two independent colonizations has also been proposed on the basis of carotid arterial patterns and myology (Bugge, 1985; Woods and Hermanson, 1985; Bryant and McKenna, 1995; McKenna and Bell, 1998; Landry, 1999; Jenkins et al., 2005) and incisor enamel (Martin, 1994). With two exceptions (see discussion of the Santa Rosa and Contamana faunas below), rodents do not occur in or prior to the Mustersan (late middle and/or late Eocene) South American Land Mammal “Age” (SALMA). The group’s presence in the high latitudes thus almost certainly postdates the Mustersan given the dense sampling of this and earlier SALMAs in the region (vucetich et al., 1999; Madden et al., 2010), even for small-bodied taxa. Caviomorphs are widely inferred to have reached South America from Africa (Lavocat, 1974, 1976; Jaeger, 1989; Martin, 1994, 2005; Marivaux et al., 2004; Coster et al., 2010; Sallam et al., 2011), via one or more crossings of a ~1000–1500 km wide South Atlantic (Houle, 1999) during the Paleogene. An earlier alternative scenario, invoking dispersal from North America via the proto-Antilles (Wood and Patterson, 1959; Wood, 1968; 1972; 1974), was predicated on the now discredited (Hoffstetter and Lavocat, 1970; Bugge, 1985; Meng, 1990; Martin, 1994) notion of a close relationship between North American franimorphs and Caviomorpha. An Asian origin for caviomorphs has been proposed on molecular and morphological grounds (Hussain et al., 1978; Flynn et al., 1986; Jaeger, 1989; Huchon and Douzery, 2001). Nevertheless, dispersal between Asia and South America via North America or Australia-Antarctica is contradicted by the lack of early Cenozoic hystricognaths in any of these locations (Hartenberger, 1985; Wood, 1985; Houle, 1999; Marivaux et al., 2002). South America’s isolation during most of the Cenozoic produced highly endemic land mammal faunas. Although this endemicity has hampered intercontinental biochronologic correlations, faunal changes have permitted recognition of a finely subdivided sequence of intracontinental biochronologic units. About 20 SALMAs spanning much of the Cenozoic are recognized (e.g., Simpson, 1940, 1950, 1980; Patterson and Pascual, 1968; Marshall et al., 1983; MacFadden, 1985; Marshall, 1985; Pascual and Ortiz Jaureguizar, 1990; Flynn and Swisher, 1995; Pascual et al., 1996; Flynn et al., 2003, 2012) (fig. 1). 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 3 Simpson (1940) subdivided the Cenozoic mammalian record into three broad “faunal strata,” based largely on the first appearance of various higher-level taxonomic groups. Simpson’s earliest subdivision (Stratum 1) is characterized by the first occurrences of “archaic” lineages: Marsupialia, Xenarthra, and endemic ungulates (e.g., certain “condylarths,” Litopterna, Notoungulata). Faunal Stratum 2 is marked by immigration of caviomorph rodents and platyrrhine primates, as well as by a “modernization” of the “archaic” lineages of Stratum 1, particularly various notoungulates. Simpson’s faunal Stratum 3 corresponds to an interval spanning the late Miocene to Recent, i.e., the “Great American Biotic Interchange.” The base of Simpson’s faunal Stratum 2, traditionally the Deseadan SALMA (Simpson, 1948, 1950, 1967, 1980), is marked by the first appearance of numerous clades, including—prior to discovery of the Tinguiririca Fauna—caviomorphs. Deseadan caviomorphs are known from sequences in Patagonian Argentina (Ameghino, 1897, 1902; Loomis, 1914; Wood, 1949; Wood and Patterson, 1959; vucetich, 1989), Bolivia (Hoffstetter and Lavocat, 1970; Lavocat, 1976; Patterson and Wood, 1982; vucetich, 1989), Peru (Shockey et al., 2009), Uruguay (Kraglievich, 1932; Mones and Castiglione, 1979), Brazil (vucetich et al., 1994; vucetich and Ribeiro, 2003) and Chile (unpublished). In addition to Tinguiririca, preDeseadan caviomorphs are also now reported from the Santa Rosa and Contamana faunas of Peru (Frailey and Campbell, 2004; Antoine et al., 2011). ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Casamayoran Mustersan Tinguirirican Deseadan 25 30 35 40 45 OLIGOCENE EOCENE FIG. 1. The transitional Eocene-Oligocene portion of the SALMA sequence (based on Flynn and Swisher, 1995; as modified by Croft et al., 2008). FIG. 2. Location map; Tinguiririca River valley, Termas del Flaco, Chile (modified from Wyss et al., 1994). 4 AMERICAN MUSEUM NOvITATES NO. 3750 Superfamily Family Taxa Age Reference number Locality Dinomyidae Scleromys quadrangulatus Santacrucian MLP 82-vI-3-2 Santa Cruz Formation, Argentina Cavioidea Pan-Dasyproctidae Incamys bolivianus Deseadan PU 2093; PU 21952 Salla-Luribay Basin, Bolivia Neoreomys australis Santacrucian - Colloncuran AMNH 9540; AMNH 9541-3 Santa Cruz Formation, Argentina Branisamys luribayensis Deseadan PU 21944 Salla-Luribay Basin, Bolivia Australoprocta fleaglei Colhuehuapian MACN 1781; 1782; 1783; 1784; 1785; 1786; 1788; 1789 Gaiman (Chubut), Argentina Dasyprocta punctata Extant AMNH 14179; AMNH 40831 Mexico, Ecuador, venezuela, Colombia, Peru, Bolivia, Brazil, Paraguay, Argentina Eoincamys pascuali ?Eocene and/or Oligocene LACM 143299; 143306; 143308 Santa Rosa, Peru Eobranisamys romeropittmanae ?Eocene and/or Oligocene LACM 143342; 143345; 144293 Santa Rosa, Peru Andemys termasi Tinguirirican SGOPv 2933 Tinguiririca Eocardiidae Chubutomys simpsoni Deseadan AMNH 29557 Cabeza Blanca (Chubut), Argentina Octodontoidea Undetermined Draconomys verai Between Deseadan and Tinguirirican MPEF-Pv 7506 Gran Barranca, Argentina Paulacoutomys paulista Deseadan MNRJ 4082-v Taubaté Basin, Brazil Sallamys pascuali Deseadan PU 20907; PU 20909 Salla-Luribay Basin, Bolivia Eosallamys simpsoni ?Eocene and/or Oligocene LACM 143276; 143414 Santa Rosa, Peru Eoespina woodi ?Eocene and/or Oligocene LACM 143281; 143390; 144294 Santa Rosa, Peru Eosachacui lavocati ?Eocene and/or Oligocene LACM 143382; 143393 Santa Rosa, Peru Deseadomys arambourgi Deseadan MNHN 1903-3-1 Cabeza Blanca (Chubut), Argentina TABLE 1. Oligocene and early Miocene caviomorphs used for comparisons in this study, with the proposed taxonomic placement of the two new taxa from the Tinguiririca Fauna (Chile) indicated. 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 5 Superfamily Family Taxa Age Reference number Locality Xylechimys obliquus Deseadan MLP 59-II-26–81 Cabeza Blanca (Chubut), Argentina Platypittamys brachyodon Deseadan AMNH 29600 Scarritt Pocket (Chubut), Argentina Migraveramus beatus Deseadan PU 21948 Salla-Luribay Basin, Bolivia Chinchilloidea Pan-Chinchillidae Eoviscaccia australis DeseadanColhuehuapian MACN CH 1877; 1878; 1882; 1883 Gaiman (Chubut), Argentina Eoviscaccia boliviana Deseadan MNHN BLv 158 (MNHN(P)) Lacayani, Bolivia Eoviscaccia frassinettii Tinguirirican SGOPv 2935 Tinguiririca Prolagostomus imperialis Santacrucian– Laventan AMNH DvP 99300; 9587 Patagonia, Argentina Lagostomus maximus Extant AMNH 41511 Argentina, Bolivia, Paraguay Cephalomiydae Litodontomys chubutensis Deseadan ACM 3086 Cabeza Blanca (Chubut), Argentina Cephalomys plexus Deseadan FAM 111480 La Flecha (Santa Cruz) and Cabeza Blanca (Chubut), Argentina Neoepiblemidae Scotamys antiquus Deseadan MNHN 1903-3-8; MNHN 1903-3-12 La Flecha (Santa Cruz), Argentina Perimys incavatus Colhuehuapian FAM 29736 Gran Barranca, Argentina 6 AMERICAN MUSEUM NOvITATES NO. 3750 In his classic treatise Tullberg (1899) subdivided rodents into Sciurognathi and Hystricognathi, based on the angle between the mandibular ramus and the vertical plane of the incisors. Hystricognathous rodents were subsequently shown to form two subdivisions based on morphological (Luckett and Hartenberger, 1993; Marivaux et al., 2002, 2004), molecular (e.g., Huchon et al., 2000, 2002, 2007; Huchon and Douzery, 2001; Murphy et al., 2001; Poux et al., 2006; Blanga-Kanfi et al., 2009), and endoparasitic (Hugot, 1999) evidence. These hystricognath subdivisions include the paraphyletic African Phiomorpha (Old World porcupines, cane rats, dassie rats) and the monophyletic South American Caviomorpha (chinchilla rats, pacas, chinchillas, capybaras, New World porcupines, agoutis, pacarana, spiny rats, tuco-tucos, cavies, hutias), a clade nested deeply within Hystricognathi. (One fossil taxon from Africa was recently assigned to the Caviomorpha; see below.) South American hystricognaths, greater in diversity than their African counterparts, evidently diversified rapidly after their arrival in the New World, contributing to the obscure phylogenetic relationships among the group’s major clades, which have been traditionally accorded family or superfamily rank. Moreover, a high degree of parallelism appears to have marked the morphological (Hartenberger, 1985) and molecular (Nedbal et al., 1996) evolution of caviomorphs, further complicating our understanding of their higher-level interrelationships. The phylogenetic placement of many modern and extinct forms thus continue to be debated, sometimes even at high taxonomic levels (Cabrera, 1961; Anderson and Jones, 1984; Corbet and Hills, 1991; Wilson and Reeder, 1993; McKenna and Bell, 1998; Woods and Kilpatrick, 2005). Molecular results indicate that Caviomorpha is divisible into four major clades: Erethizontoidea, Cavioidea, Octodontoidea, and Chinchilloidea (Huchon and Douzery, 2001; Opazo, 2005; Poux et al., 2006; Blanga-Kanfi et al., 2009). Conflicting classificatory schemes have been proposed in numerous morphologically based studies (e.g., Simpson, 1945; Landry, 1957; Patterson and Wood, 1982; McKenna and Bell, 1998; Woods and Kilpatrick, 2005). Here we adopt the classification of Woods and Kikpatrick (2005), which recognizes these four superfamilies (tables 1, 2), in part because of its congruence with molecular evidence. Over the last two decades the Andean main range of central Chile—once regarded as barren of terrestrial vertebrate fossils—has become recognized as containing one of the continent’s most important archives of Cenozoic mammal evolution (Flynn et al., 2003, 2012; Croft et al., 2008). Although the geology of the central Chilean Andes has been intensively studied for decades, and the strata now known to contain fossils are broadly exposed across the region, this rich paleontological resource was not recognized until the late 1900s. The unusually late discovery of these fossils reflects several peculiarities, including the dominance of igneous, metamorphic, and marine sedimentary rocks over terrestrial sedimentary sequences in the country; the dearth of early discoveries of vertebrate fossils; and difficult logistics. Collectively these factors delayed study of terrestrial vertebrate fossils in Chile relative to neighboring Argentina. The Tinguiririca Fauna, discovered in 1988 by a team from the AMNH and collaborating institutions, derives from outcrops north and south of the Tinguiririca River near the summer resort town of Termas del Flaco. This fauna ultimately formed the basis of a novel post-Mustersan, pre-Deseadan SALMA, the Tinguirirican (Flynn et al., 2003).5 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 7 At least one additional set of localities of Tinguirirican age occurs in the Andean main range of Chile, approximately 100 km north of Termas del Flaco near the Cachapoal River (Flynn and Wyss, 2004). The Cachapoal Fauna includes at least one rodent, and thus promises to shed additional light on the early diversification of caviomorphs once this specimen has been prepared and studied. Mammal fossils in the central Chilean Andes occur in volcaniclastic sediments of the Abanico (= Coya-Machalí) Formation and its lateral equivalents. Fossiliferous strata were likely produced as distal ignimbrites or debris flows (Croft et al., 2008). In spite of, or perhaps owing to, this unusual mode of deposition, fossils are generally fairly complete and preserve considerable anatomical detail. MATERIALS, ABBREvIATIONS, AND METHODS Materials: The impetus for this paper was the recovery of two specimens from the Termas del Flaco area of the central Chilean Andes. Although these specimens for a time represented the oldest rodents known from South America, they have not previously been fully described or named. To be permanently housed in the vertebrate paleontology collections (SGOPv) of the Museo Nacional de Historia Natural (MNHN-S), Santiago, Chile, SGOPv 2933 is designated below as the holotype of Andemys termasi, new genus and species, a taxon closely affiliated with dasyproctids. SGOPv 2935, the holotype of Eoviscaccia frassinettii, new species, is related to chinchillids. Important comparative taxa, Deseadan and slightly earlier caviomorphs to which the specimens from Termas del Flaco were compared extensively, are listed in table 1. Dental nomenclature: Nomenclature employed in the following descriptions, detailed in figures 3–6, is based largely on Frailey and Campbell (2004), Marivaux et al. (2004), Jenkins et al. (2005), and Pérez (2010). Institutional abbreviations: AMNH, American Museum of Natural History, New York; FAM, Frick Collection, American Museum of Natural History, New York; LACM, Los Angeles County Museum of Natural History, Los Angeles, California; MACN, Museo Argentino de Ciencias Naturales, Buenos Aires, Argentina; MNHN-S, Museo Nacional de Historia Natural, Santiago, Chile; MNHN-P, Muséum National d’Histoire Naturelle, Paris, France; MNRJ, Museo Nacional do Rio de Janeiro, Brazil; MPEF-PV, Museo Paleontológico “Egidio Feruglio,” paleovertebrate collection, Trelew, Argentina; MLP, Museo de la Plata, La Plata, Argentina; PU, Princeton University Collection of Yale Peabody Museum, New Haven, Connecticut; SGOPV, paleovertebrate collections of the MNHN-S, Santiago, Chile. 5 At the time the Tinguirirican SALMA was initially proposed, the “Divisaderan” was also considered to fall within the hiatus between the Mustersan and Deseadan. Fossils recovered from Divisadero Largo (near Mendoza, Argentina) in recent years, and the study of sediments adhering to specimens collected decades ago, have elegantly demonstrated that not all fossils from the region are contemporaneous. Rather, the Divisaderan “fauna” consists of a mixture of taxa that are considerably older and younger than previously assumed, invalidating the Divisaderan as a SALMA (Cerdeño et al., 2008; López and Manassero, 2008). 8 AMERICAN MUSEUM NOvITATES NO. 3750 SYSTEMATIC PALEONTOLOGY Rodentia Bowdich, 1821 Entodacrya Landry, 1999 = Ctenohystrica Huchon, Catzelflis and Douzery, 2000 Hystricognathi Tullberg, 1899 Caviomorpha Wood and Patterson, 1955 (in Wood, 1955) Cavioidea Fischer von Waldheim, 1817 Pan-Dasyproctidae (see below), Smith, 1842, author of Dasyproctidae Andemys termasi, gen. et sp. nov. Figures 3, 4; table 3 Holotype: SGOPv 2933, right mandibular fragment preserving p4–m3 and the incisor root. Referred specimens: Known only from the holotype. Etymology: Ande, in reference to the cordillera in which this taxon was found. The derivation of Andes is uncertain, but for linguistic purposes the root is treated as “Ande-” (Andes representing a Spanish language pluralization of an unknown root, although often argued to be related to the Quechua “andi” referring to mountains; C. Kammerer, personal commun.). The suffix mys, Greek for “mouse,” is commonly applied to names of rodents; the species name  Superfamilies Extant families Extinct families Africa Bathyergidae † Phiomyidae Hystricidae † Diamantomyidae Petromuridae † Myophiomyidae Thryonomyidae South America Erethizontoidea Erethizontidae Cavioidea Caviidae † Eocardidae Dasyproctidae Cuniculidae Octodontoidea Ctenomyidae † Acaremyidae Octodontidae Abrocomidae Echimyidae Myocastoridae Capromyidae Heptaxodontidae Chinchilloidea Chinchillidae † Cephalomyidae Dinomyidae † Neoepiblemidae TABLE 2. Higher taxonomic groups of caviomorph rodents recognized in the current work. Superfamilies based in part on the molecular work of Huchon and Douzery (2001), Opazo (2005), Poux et al. (2006), and Blanga-Kanfi et al., (2009). The placement of familes having extant representatives is based on Woods and Kilpatrick (2005), while those for wholly extinct clades (designated by †) are based on Hartenberger (1998) and vucetich et al. (1999). 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 9 termasi derives from Termas del Flaco, the town near which the holotype was recovered and the long-term base of operations for field research in the area. Type locality: Tinguiririca River valley, Termas del Flaco (34°57´S, 70°27´W), east central Chile (Wyss et al., 1993); Locality Set 3 (Flynn et al., 2003; “Locality C” of Charrier et al., 1996), ~1–2 km north of the Río Tinguiririca (i.e., ~5 km north of the two other Tinguiririca Fauna producing localities in the region, locality sets 1 and 2 of Flynn et al., 2003); see also Wyss et al. (1994: fig. 2), and Charrier et al. (1996). Stratigraphic occurrence: Purplish volcaniclastic sediments representing locally basal levels of the Abanico (= Coya-Machalí) Formation (Wyss et al., 1993, 1994; Flynn et al., 2003). Age: ?Late Eocene–early Oligocene, Tinguirirican SALMA. Several whole-rock 40K/40Ar dates ranging in mean age from 31.4 to 35.6 Ma (Wyss et al., 1990; Flynn et al., 2003) have been obtained from south of the Tinguiririca River. Dates from the older end of the spectrum Andemys termasi Eoviscaccia frassinettii SGOPv 2933 SGOPv 2935 p4 MD — 3.25 LL — 2.00 Dv — 1.12 m1 MD 4.00 3.37 LL 3.75 3.00 Dv 4.00 0.75 CH 1.50 — HI 0.38 — m2 MD 4.50 2.75 LL 4.00 3.00 Dv 4.25 0.50 CH 2.00 — HI 0.44 — m3 MD 4.00 3.25 LL 3.87 3.00 Dv 3.75 1.00 CH 2.37 — HI 0.59 — TABLE 3. Dental measurements (in millimeters) taken with calipers. Abbreviations: Dv, dorsoventral height (crown plus exposed portion of root for Andemys termasi, crown above gum line for Eoviscaccia frassinettii); LL, labio-lingual width (measured across center of tooth); HI, hypsodonty index = crown height (CH) divided by the mesiodistal length (MD) of the same tooth. 16 AMERICAN MUSEUM NOvITATES NO. 3750 tomys where the hypoflexid is transverse. The m3 hypoflexid of Andemys is well developed but narrow, reaching the midline of the tooth (excluding the soon to be formed metafossettid), as in Dasyprocta, Branisamys, Eobranisamys, Australoprocta, Sallamys, Xylechimys, Neoreomys, Eoincamys, and Incamys. Andemys, along with Neoreomys, Australoprocta, and Dasyprocta, differ from Incamys and Eoincamys in their labially extended metalophids on m2–3. In Andemys the anterofossettid is smaller than the mesofossettid on m2, while this size relationship is reversed on m3, perhaps reflecting differences in wear. These fossettids are similar in size on m2–3 in Eobranisamys and Branisamys. In Dasyprocta and Neoreomys the anterofossettid is more transversely elongate than the mesofossettid, but both fossettids are thinner mesiodistally than the lophids (in Andemys the fossettids and lophids are equally broad mesiodistally). The latter of these features varies little with wear. The generally low level of hypsodonty in Andemys is exhibited particularly well on the labial side of the least worn tooth, m3 (fig. 3A, 4A, B). Chinchilloidea Bennett, 1833 Pan-Chinchillidae (see below), Bennett, 1833, author of Chinchillidae Eoviscaccia vucetich, 1989 Eoviscaccia frassinettii, new species Figure 5; table 3 Holotype: SGOPv 2935, partial right mandible bearing p4–m3 and incisor. Referred specimens: Known only from the holotype. Etymology: Species named in honor of our esteemed colleague and friend, Daniel Frassinetti, who recently passed away. Daniel, a collaborator on our earliest paleontological projects in the Chilean Andes, was responsible for greatly enhancing the MNHN-S fossil vertebrate collections while chief of the paleontology section, and was an unwavering supporter of international scientific collaborations. Diagnosis (modified from vucetich, 1989): Eoviscaccia is characterized by bilobed hypsodont cheek teeth, with fossettes/ids persisting relatively late in wear; hypoflexus/id disappearing only after extreme wear; lobes triangular in occlusal outline in young and moderately worn individuals rather than rectangular as in the other pan-chinchillids; roots may incipiently close in older individuals. We amend the diagnosis of Eoviscaccia with the following observations concerning the lower dentition: in advanced wear the mesial margin of the anterior lobe becomes concave; a narrow isthmus of dentine connects the lobe pairs lingually; and the anterior lobes are thicker mesiodistally than their posterior counterparts. Enamel covers all faces of the cheek teeth but is thin on the anterior faces of both lobes on the molars, on the anterior face of the posterior lobe on the premolar, and on the labial faces of the posterior lobes of all four cheek teeth. Cementum fills the hypoflexid. The hypoflexid hooks posteriorly at its medial terminus, failing to reach the lingual side of the tooth as in most other pan-chinchillids. Diagnosis of E. frassinettii, n. sp. (figs. 5, 6; table 5): The largest lower cheek tooth in E. frassinettii is m1, whereas in E. boliviana it is m2 (E. australis is known only from isolated 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 17 Hfxd Exposed crown m3 m1 m2 p4 D A i mm 1 mm Pl Al Hfxd Atfd m3 m1 m2 p4 B P H E M C FIG. 5. Holotype of Eoviscaccia frassinettii (SGOPv 2935): (A) photograph and (B) line drawing of right p4–m3 in occlusal view; (C) photograph and (D) line drawing in labial view. Abbreviations: Al, anterior lobe; Atfd, anterofossettid, E, entoconid; H, hypoconid; Hfxd, hypoflexid; M, metaconid; P, protoconid; Pl, posterior lobe. 18 AMERICAN MUSEUM NOvITATES NO. 3750 FIG. 6. (A) Scanning electron micrograph (from vucetich, 1989), and (B) line drawing of right p4–m2 of Eoviscaccia boliviana MNHN BLv 158 (MNHN(P)). (C–F) Line drawings of the lower dentition of Eoviscaccia australis, (C) MACN CH 1883 (left m1 or m2); (D) MCN CH 1883 (left m1 or m2); (E) MACN CH 1877 (left p4); and (F) MACN CH 1878 (right p4) (after Kramarz, 2001). Multiple teeth of Eoviscaccia australis are shown to illustrate the variable presence of anterofossettids on p4 and shape variability of teeth presumably from the same locus. Abbreviations: Al, anterior lobe; Atfd, anterofossettid; Hfxd, hypoflexid; Pl, posterior lobe. The angled arrow indicates anterior and lingual directions. Scale bars = 1 mm. m1 or m2 p4 Atfd Pl Al Hfxd m1m2 p4 Atfd Pl Al Hfxd AB C D E F p4 m1 or m2 teeth). The hypoconid region is more rectangular labially in E. frassinettii than in E. boliviana and E. australis. The m1–2 protoconid region is oblique in E. frassinettii and E. boliviana (slightly less so in the latter), but transverse in E. australis. The anterior face of p4 is sheathed in enamel in E. frassinettii whereas this region is bare (or the enamel is greatly reduced) in E. australis and E. boliviana. As in E. boliviana and E. australis, enamel occurs on the lingual faces of the anterior lobes of the lower molars in E. frassinettii (although this enamel thins in late wear at least in the former two taxa). Furthermore, in SGOPv 2935, whatever its precise stage of wear, the lophids are oblique rather than transverse (compared to E. boliviana and E. australis), and the p4 anterofossettid appears to persist later in wear, filling with cement. DESCRIPTION AND COMPARISON The holotype of E. frassinettii preserves the incisor and p4–m3, but the posterior extremity of m3 is missing. Much of the slender incisor (visible in occlusal and lateral view) and the diastema remain covered in sediment, but the latter appears to be roughly as long as the cheektooth row. Premolar (figs. 5, 6): This tooth is bilobed, as are the molars. The anterior lobe is roughly pear shaped in outline, while the mesiodistally broader and more transverse posterior lobe is reniform. The posterior margin of the anterior lobe is oblique labially but becomes transverse 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 19 lingually; a posteriorly directed hook marks its lingual terminus. The hypoflexid of p4 is less oblique than that of the other cheek teeth. The pearand reniform-shaped outlines of the two lobes on p4 in E. frassinettii are similar to those of E. boliviana, E. australis, and Perimys. An anterofossettid occurs on p4 of E. frassinettii, as in little to moderately worn specimens of E. boliviana, E. australis, and Scotamys; in E. frassinettii, however, the anterofossettid is filled with cementum. Enamel is reduced on the anterior and labial faces of the posterior lobe as in E. boliviana and E. australis; enamel is reduced, however, on the anterior face of the anterior lobe of p4 in E. boliviana and E. australis, whereas in E. frassinettii a continuous sheet of enamel is present. The hypoflexid nearly reaches the lingual face of enamel—in the other two species the separation between these structures is greater. First and second lower molars (figs. 5, 6): The first two molars are similar in morphology, m1 being slightly larger. They are rhomboidal in occlusal outline, contrasting with the more triangular p4. They are nearly identical in width, both being slightly broader than p4. The lingual margins of m1–2 are straight. The posterior margins of both lophids are parallel. The anterior lophid of m1 forms a rough isosceles triangle, its vertex directed labially, while on m2 it is reniform. The anterior margins of the anterior lobes of m1–2 are mildly concave, somewhat more so on m1. The posterior margins of the anterior lobes are transverse lingually, becoming more oblique labially. The posterior lophids of m1–2 are reniform and convex posteriorly, more strongly on m2 than m1. The protoconid regions of both teeth are roughly triangular while the hypoconid regions are more quadrate. Lingually m1 is more squared and longer anteroposteriorly than labially; m2 is equally long lingually and labially. As on the other cheek teeth, a distinctive enamel hook projects posteriorly from the lingual end of the hypoflexid. Enamel is discontinuous across the anterior face of both lobes and the labial face of the posterior lobe on all molars; it is roughly twice as thick on the posterior margins of the cheek teeth as elsewhere. The hypoconid region is more rectangular in E. frassinettii than in E. boliviana and E. australis. The anterior lobes are slightly to substantially longer mesiodistally than the posterior ones, as in other members of the genus. The protoconid regions of m1–2 are slightly more oblique in E. frassinettii than in E. boliviana; in E. australis this region is transverse. In SGOPv 2935 enamel occurs on the lingual faces of both lobes, whereas this covering is reduced in E. boliviana and E. australis in advanced wear. The hypoflexids of SGOPv 2935 do not reach the lingual sides of the teeth, being isolated from the latter by a thin isthmus of dentine after minimal wear, as in E. australis and E. boliviana. Third lower molar (figs. 5, 6): Only the anterior part m3 of SGPv 2935 is preserved. The anterior lobe is oriented obliquely (as on m1–2), is triangular in outline (as on m1), and bears a thicker enamel rim lingually than labially. Lingually, the anterior lobe is broader mesiodistally than its counterparts on m1–2. The posterior rim of the anterior lobe fails to reach the tooth’s lingual margin, becoming incorporated in a posteriorly directed enamel hook (as on the preceding teeth), a primary distinction between Eoviscaccia other pan-chinchillids. The hypoflexid nearly reaches the lingual wall of enamel after wear, terminating slightly more lingually than on m1 and m2 (m3 is unknown for E. australis and E. boliviana). 20 AMERICAN MUSEUM NOvITATES NO. 3750  Characters Andemys Australoprocta Incamys Branisamys Eobranisamys 1 Tetralophodonty + + + + + 2m1, all fossettids rounded + - - - - 3m1 fossettids centrally positioned + - - - - 4m1 posterolophid half the width of the anterolophid + - - - - 5m1-m2 metafossettid present + + + + + 6m3 metafossettid/hypoflexid confluent + + + + + 7m3 mesofossettid smaller than anterofossettid + + + + + 8m2 hypoflexid well-developed but narrow, reaching the tooth’s midline + + + - - 9Fossettids narrow mesiodistally compared to the lophids + + - - - 10 Squared lower molars + + - - - 11 Slightly hypsodont + - - - + 12 Lophids and fossettids transverse + - - + - 13 Labial cusps rounded + - - - - 14 Hypoflexid compressed labially + - - - - TABLE 4. Diagnostic characters of Andemys and their absence (-) /presence (+) in compared taxa.  Characters E. frassinettii E. boliviana E. australis 1Hypoconid region rectangular labially + - - 2m1 the largest lower cheek tooth + - 3Protoconid region on m1-2 oblique + + - 4Anterior face of p4 sheathed in enamel + - - 5Enamel on lingual faces of the anterior lobes remains thick into late wear + - - 6Lophids oblique + - - 7p4 anterofossettid persists late in wear filling with cement + - - TABLE 5. Diagnostic characters of Eoviscaccia frassinettii and their absence (-) /presence (+) in the two other other species of the genus. DISCUSSION Andemys termasi: Among pre-Pliocene and living caviomorphs, Andemys most closely resembles Dasyprocta, Australoprocta, Neoreomys, Eoincamys, Incamys, Branisamys, and Eobranisamys. A mental foramen, when present in caviomorphs, is positioned either high on the mandible within the diastema, well anterior of p4, as in Incamys, Dasyprocta, Neoreomys, and Eobranisa- 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 21 mys (pan-Dasyproctidae), Chubutomys (Eocardiidae), and Scleromys (Dinomyidae), or below the roots of p4, as in Draconomys, Platypittamys, Eoespina, Migraveramus, and Sallamys (Octodontoidea). Andemys is characterized by the former condition (fig. 3), arguing against the echimyid affinities suggested for it by Frailey and Campbell (2004). In Andemys the anterior arm of the hypoconid (cristid obliqua) does not separate the hypoflexid and the metafossettid until late wear, as is also the case in Dasyprocta, Incamys, Eoincamys, and Australoprocta. In Neoreomys, Branisamys, and Eobranisamys, this separation occurs earlier in wear. The lingual part of the hypoflexid lies between the mesoand metafossettid in Andemys, as in Incamys, Eoincamys, Neoreomys, Australoprocta, Branisamys, and Eobranisamys. A hypoconid arm occurs consistently on the molars of pre-Miocene octodontoids such as Sallamys, Eosachacui, Eoespina, and Eosallamys (in all stages of wear). This arm occurs on m1–2 of Andemys, but it is absent on m3 (the least worn tooth) (fig. 3B, D, E). The lower molars of Andemys maintain four lophids fairly late into wear (as do those of Branisamys, Eobranisamys, Neoreomys, and Australoprocta) and bear long hypoflexids (as do Incamys, Dasyprocta, Neoreomys, and Australoprocta). Andemys resembles Australoprocta in several respects. The lower molars of both taxa become squared and narrow transversely in advanced wear, the fossettids are narrow mesiodistally compared to the lophids, and the labial cusp regions become enlarged. In contrast to Australoprocta, however, the lophids and fossettids of Andemys are transverse (they are oblique in Australoprocta), the labial cusps are rounded (rather than angular as in Australoprocta), and the hypoflexid is anteroposteriorly compressed labially (it is broadly open in Australoprocta). Finally, Andemys is substantially less hypsodont than Australoprocta (see figs. 3, 4; table 4). Higher-level taxonomic assignment of Andemys: Fitting Andemys into existing caviomorph taxonomies poses a number of challenges, some stemming from uncertainties about phylogenetic relationships, and some from a previous lack of attention to the definitions of supraspecific taxon names. Although Andemys is obviously a member of the Caviomorpha, it is not immediately apparent to which of the four currently recognized “superfamily” or 12+ “family”-level groups it belongs or is most closely affiliated. As mentioned, the poorly resolved interrelationships of many of these groups poses one difficulty; of particular relevance here are the debated affinities of many early diverging extinct taxa to the various crown clades. A second problem of assigning Andemys to a recognized “family” stems from the scant attention that has been paid historically to the definitions of the names themselves. Andemys resembles a variety of Oligocene, Miocene, and evidently late Eocene taxa, including, Australoprocta, Branisamys, Eobranisamys, Scleromys, Neoreomys, Eoincamys, and Incamys, all of which have been referred to the Dasyproctidae at least on occasion. Nevertheless, assignment of most of these taxa to the Dasyproctidae has been questioned for a variety of reasons, including issues related to the proper conception of the name Dasyproctidae. (We follow Patterson and Wood, 1982, and most of the recent literature on fossil caviomorphs in using the name Dasyproctidae rather than Agoutidae; see also Woods and Kilpatrick, 2005.) The higher-level placements of many of the taxa with which we have compared Andemys closely are controversial. Scleromys exemplifies the highly unstable phylogenetic position of 22 AMERICAN MUSEUM NOvITATES NO. 3750 many fossil caviomorphs. Fields (1957) considered Scleromys a dinomyid, the latter of which had long been generally regarded as cavioids. Other researchers considered Scleromys a dasyproctid—and hence still a cavioid (Miller and Gidley, 1918; Wood and Patterson, 1959). Thus, although the familial assignment of Scleromys was disputed, there was general agreement about its suprafamilial placement (Cavioidea). More recently, however, molecular evidence points to membership of Dinomys, the sole extant dinomyid, within the Chinchilloidea rather than Cavioidea (Huchon and Douzery, 2001). This poses the question of whether extinct taxa such as Scleromys should be transferred to Chinchilloidea along with Dinomys, assuming the dinomyid affiliation of Scleromys is accepted. Kramarz (2006) followed Fields (1957) in assigning Scleromys to the Dinomyidae, but he maintained the traditional placement of the Dinomyidae within Cavioidea rather than Chinchilloidea, in conflict with molecular evidence. In short, the familial (Dinomyidae or Dasyproctidae) and superfamilial (Chinchilloidea or Cavioidea) affinities of Scleromys may thus be seen as highly uncertain. The fluctuating familial and superfamilial assignments of Branisamys illustrate a similar problem: this taxon has been considered, in turn, a dasyproctid (Hoffstetter and Lavocat, 1970), a dinomyid (Patterson and Wood, 1982), and an “agoutid” (Frailey and Campbell, 2004). (The placement of Incamys, Eoincamys, and Neoreomys are plagued with similar uncertainties.) Resolution of these and myriad other classificatory questions awaits comprehensive phylogenetic analyses of the taxa involved. As noted above, at the center of many of these problems are several early putative dasyproctids. A strong case can be made that the name Dasyproctidae should apply to the leastinclusive clade of which the extant Dasyprocta and Myoprocta are members (consistent with the usage of Simpson, 1945; Landry, 1957). (This conception of the name, incidentally, agrees with recent recommendations that well-known taxonomic names apply to crown clades; see below.) Miller and Gidley (1918) and Wood and Patterson (1959) referred the Miocene Neoreomys and its apparent close relatives, Scleromys and Olenopsis, to the Dasyproctidae and, given that such matters were not considered important at the time, they did so without concern for whether extinct forms nested within the crown clade. For the sake of argument we may assume that Neoreomys is a proximal outgroup to (Dasyprocta + Myoprocta), as supposed by Wood and Patterson (1959) though not articulated as such (since their work took place prior to the invention of cladistic methods and terminology). We may also assume a similar phylogenetic placement for Andemys. Whether these extinct taxa are termed “dasyproctids” thus hinges simply on the question of how the name “Dasyproctidae” is defined. There is growing consensus that widely used taxonomic names are most appropriately applied to crown clades, rather than to crown clades plus their stems or portions of their stems (de Queiroz and Gauthier, 1992). Consistent with Simpson (1945) and Landry’s (1957) views, Dasyproctidae should therefore be tied to the clade encompassing the most recent common ancestor of Dasyprocta and Myoprocta plus all its descendants. Numerous tools for defining taxonomic names phylogenetically currently exist (de Queiroz and Cantino, 2001), none of which, to our knowledge, have been applied to caviomorphs. (The name “Caviomorpha” itself is in desperate need of a phylogenetic definition, a task complicated slightly by the poorly resolved branching sequence at the base of the relevant crown clade.) Although it is tempting to propose definitive phylogenetically 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 23 based names to the groups of organisms discussed here, we feel that doing so would be premature. Our objective here is limited to describing two new fossil caviomorphs, identifying them with the specificity that the preserved material and current taxonomic practices permit, not to provide a comprehensive phylogenetic taxonomy of the major clades of caviomorphs. With regard to the taxonomic placement of Andemys, as detailed elsewhere, we contend that it is more closely allied to the minimally inclusive clade of which Dasyprocta and Myoprocta are members than with any other living caviomorphs. This poses the practical problem of what name should attach to the clade encompassing Andemys and the dasyproctid crown, but that excludes most other caviomorphs, a task complicated by the lack of a comprehensive phylogenetic analysis of Dasyprocta and Myoprocta and their potentially related extinct taxa. Despite these obstacles, as a provisional measure we propose the term “pan-Dasyproctidae” to informally refer to the dasyproctid total clade, that is, the clade consisting of the dasyproctid crown plus all taxa sharing a more recent common ancestor with that crown than with any other caviomorph crown clade(s) (de Queiroz, 2007). The precise wording of such a definition can be formalized at a later date, but for the moment this convention simplifies the task of referring to this particular clade of caviomorphs succinctly. In a parallel fashion we employ the name panChinchillidae to refer informally to the chinchillid total clade; see above. Besides Chinchillidae and Dasyproctidae, other caviomorph “families” merit having their crown clades and total clades bear different names. Nevertheless, since our immediate objective here is to provide a taxonomy for a chinchillid and a dasyproctid ally, we have treated all other caviomorph “family”-level names in the traditional fashion, not restricting them to their respective crown clades. It should also be noted that the placement of Dasyproctidae within Caviomorpha has varied historically. Wood and Patterson (1959) transferred the family from the Cavioidea, its traditional placement, to the Chinchilloidea. Patterson and Wood (1982) reversed course, returning Dasyproctidae (along with Dinomyidae) to the Cavioidea, cementing the view that both families represent early cavioid offshoots. Leaving aside ambiguities about how the name Dasyproctidae has traditionally been employed, the affiliation of Andemys to this clade, as originally proposed (Wyss et al., 1993), has been questioned (Frailey and Campbell, 2004). Frailey and Campbell (2004: 99) assigned SGOPv 2933 to the Echimyidae based on (1) “a deep hypoflexid, which is equal in length to the opposing flexids and which terminates at the base of the hypolophid,” and (2) “four slightly oblique lophids, of which the anterior two are the first to fuse and form a single lophid.” It may be noted that the first condition applies only to m2 of SGOPv 2933, not to the other molars (fig. 3B, D, E). More importantly, several early octodontoids lack hypoflexids of this form (e.g., Sallamys, Eosallamys, Eosachacui), making it unclear what condition typifies this clade ancestrally. Regarding the second feature, the anteroand metalophids are the first lophids to fuse in a wide variety of early caviomorphs including Incamys, Australoprocta, Neoreomys, Cephalomys, Eoviscaccia, Scleromys, Sallamys, and Platypittamys. The feature is thus very likely primitive for Caviomorpha and certainly not restricted to Octodontoidea. It should also be emphasized that the two anterior lophids of m2–3 on SGOPv 2933 remain decidedly unfused (m1 is highly worn, so the condition of its anterior lophids cannot be assessed; fig. 3B, D, E). With additional wear the anteroand metalo- 24 AMERICAN MUSEUM NOvITATES NO. 3750 phids would have merged increasingly as the anterofossettid diminished. The anteroand metalophids initially merged labially, increasing the apparent size of the protoconid region. Later in wear the anterofossettid would have been obliterated (shifting lingually in the process), resulting in complete fusion of the two anterior lophids, the lingual limits of the protoconid no longer being discernable. The first significant fusion to take place on m2 would have been between the hypoflexid and the metafossettid. Finally, we note that in Andemys the hypoflexid projects ventrally beneath the hypolophid, as is common to Dasyprocta, Incamys, Eoincamys, Neoreomys, Branisamys, and Eobranisamys (all of which are widely considered dasyproctids—or pan-dasyproctids in the terminology preferred here) rather than under the metafossettid as in octodontoids, including Scleromys (Kramarz, 2006). On the least worn tooth of SGOPv 2933, m3, the hypoflexid, and metafossettid are confluent, forming a common trough (fig. 3B, D, E). These structures are confluent during early wear in other pan-dasyproctids,in early dinomyids (e.g., Potamarchus), in early pan-chinchillids (e.g., Eoviscaccia), and in some (Protadelplomys) but not all (e.g, Eosachacui, Eoespina, Eosallamys, Paradelphomys) octodontoids. On balance, and as is more fully discussed below, the totality of evidence indicates that Andemys shares closer affinities with dasyproctids than with octodontoids. Eoviscaccia frassinettii: The lower cheek teeth of Eoviscaccia frassinettii consist of two large lophids or lobes (fig. 5) as in Perimys, Scotamys, the lagostomines (Lagostomus and Prolagostomus), and worn individuals of E. boliviana and E. australis, contrasting with the figure eight–shaped arrangement in Cephalomys and Litodontomys. The largest cheek tooth of E. frassinettii is m1 (figs. 5, 6), whereas in E. boliviana it is m2 (the condition for E. australis is unknown). In E. frassinettii enamel is uniformly distributed around the lower cheek teeth, whereas in other species of the genus enamel is thin or discontinuous on the anterior faces of both lobes of m1–3, on the anterior face of the posterior lobe of p4, and on the labial faces of the posterior lobes of all known lower cheek teeth (figs. 5, 6). With wear the two lophids become separated by a hypoflexid as is typical of chinchillids and neoepiblemids. Cementum fills the hypoflexid, as in E. boliviana, E. australis, Perimys, Prolagostomus, and Scotamys (partially). Although the cheek teeth of SGOPv 2935 are moderately worn, enamel extends below the alveolar border, indicating a substantial degree of hypsodonty (figs. 5, 6). Furthermore, the hypoflexid nearly reaches the lingual wall of enamel, another indicator of hypsodonty—seen also in E. australis (vucetich, 1989). Although similar to the E. boliviana and E. australis, E. frassinettii is nevertheless distinct from both. In E. frassinettii (1) the cheektooth lobes are oblique rather than transverse, (2) a cementum-filled anterofossettid persists late into wear on p4, (3) enamel is thicker lingually on both lobes (than in the other two species), (4) the hypoconid region is rectangular (rather than rounded), (5) the hypoflexid nearly reaches the lingual side of p4 and m3 (on m1–2 it terminates slightly more labially), and (6) enamel occurs on the anterior face of p4 (reduced in the other two species). This combination of features is unique to E. frassinettii (see figs. 5, 6; table 5). Eoviscaccia compares more closely to Scotamys and Perimys (Neoepiblemidae) than to Cephalomyidae, despite the lophids being substantially thinner in Scotamys and Perimys than 2012 BERTRAND ET AL.: EARLY OLIGOCENE TINGUIRIRICA RODENTS 25 in Eoviscaccia. Enamel forming the posterior margins of the anterior and posterior lobes of Eoviscaccia is thick (compared to the anterior margins), whereas in Scotamys and Perimys enamel is uniformly thick. In Eoviscaccia the lobes are tightly appressed and the hypoflexid is very thin (the typical “chinchillid” pattern), compared to Scotamys and Perimys wherein the lobes are separated by a comparatively broad hypoflexid (the neoepiblemid pattern). Hoffstetter (1971) referred specimens now regarded as pertaining to E. boliviana either to the Chinchillidae (resembling Scotamys) or the Eocardiidae. vucetich (1989) assigned E. boliviana and E. australis to the Chinchillidae. Kramarz (2001), reporting important additional material of E. australis (known only from two teeth until that time) affirmed this taxon’s placement in the Chinchillidae. vucetich (1989) regarded E. boliviana (Deseadan) as the most “primitive” and E. australis (Deseadan-Colhuehuapian) as the most “derived” member of the genus based on levels of hypsodonty (greater in E. australis), the lack of anterofossettids (in E. australis), and a hypoflexid that completely traverses the teeth basally (in E. boliviana the hypoflexid fails to reach the lingual wall of enamel in late wear, whereas in E. australis it very nearly does). An anterofossettid occurs on p4 in E. frassinettii (likely a shared plesimorphy with E. boliviana), and the hypoflexid very nearly reaches the lingual part of this tooth in late wear (approaching the condition seen in E. australis). This latter feature suggests that the level of hypsodonty in E. frassinetti roughly matches that of E. australis, whereas that in E. boliviana is lower (figs. 5, 6). Hypsodonty: Tinguirirican faunas represent the earliest global occurrence of mammalian communities dominated by highly hypsodont herbivores. High levels of hypsodonty were attained across a diversity of taxa some 15–20 million years earlier in South America than on other continents (Patterson and Pascual, 1968; Simpson, 1980; MacFadden, 1985; Pascual et al., 1996; Flynn et al., 2003; Croft et al., 2008; Zucol et al., 2010). This suggests a correspondingly early paleoenvironmental shift from closed forests to sparse trees and extensive open habitats on this landmass (Croft, 2001; Flynn et al., 2003; Croft et al., 2008), a conclusion supported by notoungulate postcranial evidence (Shockey and Flynn, 2007). The traditionally accepted notion that the development of hypsodonty is tied to the spread of grasslands has recently been called into question on the basis of paleobotanical evidence from Argentina (Strömberg et al., 2010). Phytolith assemblages in the Sarmiento Formation at Gran Barranca indicate that grass-dominated habitats did not occur there until after the late early Miocene (18.5 Ma), implying that other factors must have driven the origin of hypsodonty in the region—perhaps simply the appearance of “open,” nongrassy habitats. In sum, the Tinguiririca Fauna demonstrates that levels of hypsodonty in South American native ungulates increased dramatically near the Eocene-Oligocene transition. This coincides roughly with the paleoclimatic and paleoenvironmental changes of the earliest Oligocene “climatic deterioration” event (Prothero and Berggren, 1992). At least one of the rodents from the Tinguirirican Fauna (Eoviscaccia) exhibits a similar tendency toward precocial hypsodonty. 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