A new Hypsodont Notoungulate (Hegetotheriidae, Pachyrukhinae)
from the late Miocene of the Eastern Cordillera,
Salta province, Northwest of Argentina

Marcelo A. Reguero1, Adriana M. Candela1, Claudia I. Galli2,
Ricardo Bonini1, Damián Voglino3,

1 CONICET, División Paleontología de Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina.
regui@fcnym.unlp.edu.ar; acandela@fcnym.unlp.edu.ar; rbonini@fcnym.unlp.edu.ar

2 Facultad de Ciencias Naturales, Universidad Nacional de Salta, Avda. Bolivia 5051, Salta (4400), Argentina.
claudiagalli@fibertel.com.ar

3 Museo de Ciencias Naturales “Rvdo. P. Antonio Scasso”, Don Bosco 580, San Nicolás de los Arroyos, Buenos Aires, Argentina.
dvoglino@fundacionoga.org.ar

Fig. 1. Geography and geology of the Palo Pintado Formation. Left: map showing location of Quebrada Peñas Blancas in Salta. Right: measured stratigraphical column of the Palo Pintado Formation at Quebrada Peñas Blancas and the mammal-bearing horizon (star).

 

Assignment of the Palo Pintado hegetotheriid to the subfamily Hegetotheriinae is precluded by the morphology of m3 and the small size; the Palo Pintado taxon has a trilobed m3, whereas in all known hegetotheriines this tooth is sharply bilobed.

Hegetotheriid pachyrukhines are similar in size to other small- to medium- sized notoungulates, i.e., interatheriids, and some of the later representatives were very similar to modern rabbits (leporids) or certain ‘caviomorph rodents’ (e.g., Lagostomus, Dolichotis) in overall morphology (Sinclair, 1909; Kraglievich, 1926; Elissamburu, 2004). The hegetotheriids become abundant during the late Oligocene Deseadan SALMA (Loomis, 1914; Simpson, 1945). They are last recorded in the Pleistocene of Argentina (Cerdeño and Bond, 1998). Two sub-groups are generally recognized within Hegetotheriidae: Hegetotheriinae and Pachyrukhinae (Simpson, 1945). Pachyrukhinae is universally considered monophyletic (Cerdeño and Bond, 1998) and the clade is certainly recognizable as early as the Deseadan SALMA (Loomis, 1914; Simpson, 1945; Reguero et al., 2007b). In contrast, Hegetotheriinae is likely paraphyletic, though it may include a monophyletic subset of Miocene taxa (Cifelli, 1993; Flynn et al., 2002; Croft et al., 2004; Croft and Anaya, 2006; Reguero and Prevosti, 2010).

Herein is described a new species of Paedothe-rium from the late Miocene Palo Pintado Formation, Salta province, Argentina. The new species provides insight into Pachyrukhinae diversity during the Neogene and allow valuable comparisons between low latitude late Miocene faunas and similarly aged middle-high latitude faunas. In addition, the presence of a hypsodont fossil ungulate species in a forested environment is discussed.

2. Materials and methods

The specimen of the new species described below is housed in the vertebrate paleontology collections of the Museum of San Carlos, Salta pro-vince, Argentina. Measurements of this and other specimens were made to the nearest 0.1 mm using digital calipers, unless otherwise noted. Comparative data were gathered from collections research at the Museo de La Plata (Argentina); additional data were gathered from published sources.

Hypsodont dentition is characterized by high-crowned teeth, as opposed to brachydont dentition, which is low-crowned. Hypselodonty refers to ever-growing, rootless or open-rooted dentition. Hypsodonty index follow Reguero et al. (2007a), and were calculated by dividing the m1 height by the m1 anterobuccal-posteriorlingual length.

S.Sal.Scar.Paleo.2012-045 was found in situ in the sandy facies of the bearing horizon and the adhering matrix is a fine sandstone which was deposited by large subaqueous dunes in fast-flowing confined channels (Fig. 2). Further, the preservation of this specimen indicates that it was no transported far, and there are no other potential source horizons in the immediate vicinity. Some taphonomic characteristic of the teeth show no abrasion by sedimentary transport, i.e., 1. the amount and distribution of cementum (dentine-cementum boundary indicated in figure 3) is normal and suggests that little abrasion has occurred; 2. no rounding and no enamel loss at the edges of occlusal surfaces; 3. no removal of enamel along the salient angles. Histologic features of the crowns teeth also indicate that little, if any, dentine has been removed, other than by normal processes of occlusal attrition.

Institutional Abbreviations: MLP: Museo de La Plata, Buenos Aires, Argentina. S.Sal.Scar.Paleo: Museo de San Carlos, Salta, Argentina.

Other Abbreviations: Lower tooth loci are indicated by lower case letters (e.g., p2, m1). HI: hypsodonty index. SALMA: South American Land Mammal Age, Stage/age; cronostatigraphic unit.

 

Fig. 2. Paedotherium kakai, holotype, S.Sal.Scar.Paleo.2012-045 in situ in the sandy facies of the bearing horizon and the adhering matrix is fine sandstone which was deposited by large subaqueous dunes in fast-flowing confined channels.

 

 

Fig. 3. Paedotherium kakai, holotype, S.Sal.Scar.Paleo.2012-045; right mandibular fragment with p4-m3; A. Labial view; B. Occlusal view; C. Lingual view. Scale bars=1 cm.

 

3. Geographic and geologic setting

The Eastern Cordillera area in Argentina is situated to the northwest between 22°05’ and 27°00’S and 64°40’ and 66°10’ W; it represents the southern extremity of the same mountain range known from Bolivia. The narrow, NS trending Angastaco basin is located in the distal part of a once contiguous Paleogene Retroarc Foreland basin (Jordan and Alonso, 1987). The Angastaco basin is located in the southern part of the Eastern Cordillera. This basin includes >6 km of Eocene-Pliocene continental clastic strata of the Payogastilla Group (e.g., Díaz and Malizzia, 1983; Starck and Vergani, 1996). This basin is bounded to the west by the Precambrian-early Cambrian metasedimentary Puncoviscana Formation over the Cenozoic basin strata. To the east, the Cretaceous rocks of the Sierra de Los Colorados over the basin strata (e.g., Carrera and Muñoz, 2008). The Palo Pintado Formation comprises fluvial systems deposits which are well exposed at Peñas Blancas outcrops. The lithofacies boundaries and the characteristics and geometries of the architectural elements are documented in the stratigraphic column (Fig. 1). We interpret these facies as the deposits of laterally unstable shallow gravelly channels, perhaps in a braided fluvial system (e.g., Miall, 1996).

The Palo Pintado Formation (ca. 10 to 5 Ma) consists of ~1,200 m of colored fine to medium-grained sandstone beds with trough cross-stratified sandstones interpreted as fluvial channel sand bodies (e.g., Davis, 1983).

The geological context and the stratigraphic profile of the Palo Pintado Formation at the Quebrada Peñas Blancas area are fully detailed in figure 1. The new fossil material comes from about 410 m above the base of this unit, close to a left tributary of the Calchaquí River (Fig. 1). The age of this formation range between 10.29±0.11 Ma (Galli et al., 2008, 2011) below the bearing horizon, and 5.27±0.28 Ma (Coutand et al., 2006) and 5.98±0.32 Ma (Bywater-Reyes et al., 2010) on the top of the unit. Magnetostratigraphic study in progress of the Palo Pintado Formation has dated the mammal-bearing horizon at ca. 8.8 Ma (personal communication, C. Galli, 2013). This formation is correlated with the Guanaco Formation in the La Viña area (Sierra de Los Colorados) that has been dated at 8.73±0.25 Ma by K-Ar on biotite from an ash (Del Papa et al., 1993) and by zircon U-Pb at 9.31±0.31 Ma (Hain et al., 2011).

The Palo Pintado Formation at Quebrada Peñas Blancas is gradational with the Angastaco Formation (Fig. 1) and consists of ca. 1,000 m of green mud rocks and sandstones interbedded with green ripple- and planar-laminated mudstones interpreted as associated to a relatively fine grained, nonmarine setting with meandering stream (Galli et al., 2011). The fluvial system interpreted for this unit is intermediate between fluvial braided (with low sinuosity and simple channels) and meandering rivers (with high sinuosity and multiple channels) (Miall, 1996).The trough cross-stratified conglomerates and sandstones were deposited by large subaqueous dunes (or large 3D ripples) in fast-flowing confined channels.

4. Systematic paleontology

Class MAMMALIA Linnaeus, 1758
Order NOTOUNGULATA Roth, 1903
Suborder TYPOTHERIA Zittel, 1893
(sensu Reguero and Castro, 2004)
Family HEGETOTHERIIDAE Ameghino, 1894
Subfamily PACHYRUKHINAE Kraglievich, 1934
(see diagnosis in Cerdeño and Bond, 1998)
Genus PAEDOTHERIUM Burmeister, 1888
PAEDOTHERIUM KAKAI sp. nov.
Figure 3

Holotype: S.Sal.Scar.Paleo.2012-045, right mandibular fragment with p4-m3.

Diagnosis: Similar in size to P. typicum and P. bonaerense. The fourth premolar (p4) proportionally longer than the molars, exhibits the trigonid more rounded than P. typicum and P. bonaerense. Differs from all other species of Paedotherium in having no cementum on the molariforms and the cheek teeth are less hypsodont (HI: 2.6) than P. typicum and P. bonaerense. The third molar (m3) is narrower, with shallow labial sulci and the last lobe is smaller and more rounded than P. typicum and P. bonaerense.

Etymology: kakai, from Cacán language spoken by Diaguitas and Calchaquíes tribes who inhabited the Valle Calchaquí, Salta province, this language became extinct since the mid-17^th century or beginning of 18^th century. When the Inca started extending their empire southwards in the 15^th century, the Diaguita fiercely resisted the invasion.

Type Locality: Quebrada Peñas Blancas (S 66° 09.42’4.81’; W 25°67.18’5.43’ and 1,857 m a.s.l.).

Age and Distribution: Palo Pintado Formation, Quebrada Peñas Blancas, Salta Province, northwest Argentina, Huayquerian (late Miocene) age.

Three species of Paedotherium are currently recognized (Cerdeño and Bond, 1998): P. minor from the late Miocene Chasicoan and Huayquerian stage/ages, P. typicum and P. bonaerense from Huayquerian.

Description: S.Sal.Scar.Paleo.2012-045 consists of a partial right mandible that has been partially prepared. Most of the horizontal ramus is preserved. The alveolar and inferior margins are roughly parallel, with the depth of the mandible averaging approximately 11.5 mm. All teeth are fully erupted and have undergone moderate wear, indicative of a fully mature animal.

Paedotherium kakai is similar to P. typicum in morphology and is comparable in size. It was compared with the lectotype of P. typicum, MLP 12-1782, from the Montehermosan Stage/age of Buenos Aires Province, Argentina (Fig. 4).

The fourth premolar (p4) of Paedotherium kakai is similar to P. typicum in morphology but is less molariform, it has a very simple occlusal surface and exhibits a single deep labial sulcus separating the trigonid from the talonid. The sulcus is open and the lingual extremity has closely appressed sides. The talonid is wider than the trigonid in both p3 and p4 but is similar to it in length (mesiodistal). The lingual face of p4 is slightly convex. Enamel is absent from the distolingual and mesial surfaces, no cement covers the labial surface.

The molars are subequal in size, but gradually decrease from m1-m3. The first (m1) and second lower (m2) molars closely resemble p4 in size and morphology except that the lingual faces are slightly less convex and the labial sulci are deeper, extending more than halfway across the tooth. These attributes give the impression of a more slender tooth, but this is not reflected in dental measurements (Table 1).

The morphology of m3 is the most notable aspect of the dentition of P. kakai. A labial sulcus separating the trigonid and the talonid, and a second shallow labial sulcus is present in approximately the middle of the talonid. The resulting ‘trilobed’ condition is common to all pachyrukhines but the shape and locations of the sulci is variable between the species.

Comments: In overall morphology, Paedotherium kakai is similar to P. typicum. The most obvious difference between these two species is in morphology is the shape of the lobes and the locations of the labial sulci that conforms the tooth. Paedotherium kakai is a large pachyrukhine, but is significantly smaller than the Deseadan SALMA (late Oligocene) species Prosotherium garzoni and Medistylus dorsatus from Patagonia, the largest member of the subfamily; it is similar in size to P. typicum and P. bonaerense, overlapping in size some specimens described by Cerdeño and Bond (1998). Beyond of size features, the combined morphological difference cited in the diagnosis, clearly distinguish Paedotherium kakai from all previously described Neogene pachyrukhines.

 

Fig. 4. Occlusal views of right p4-m3 series of A. Paedotherium kakai (holotype, S.Sal.Scar.Paleo.2012-045); B. Paedotherium typicum (lectotype, MLP 12-1782); C. Paedotherium minor (MLP 30-XII-10-29); D. Tremacyllus impressus (MLP 57-X-10-55). Scale bar=1cm.

 

5. Discussion

5.1. Biostratigraphic and biogeographic significance of the genus Paedotherium

Pachyrukhines are extremely common in the Miocene and Pliocene of Argentina. From the late Miocene (Chasicoan/Huayquerian) to late Pliocene (Marplatan), only two genera are represented, Paedotherium and Tremacyllus.

Paedotherium is best known from the rich Chasicoan and Huayquerian (late Miocene) deposits along the Atlantic coast of Buenos Aires. The temporal record of Paedotherium ranges from late Miocene to late Pliocene of Argentina, Chile and Bolivia; it is one of the most abundant mammals in Montehermosan and Chapadmalalan faunas of the Buenos Aires (Monte Hermoso, Chapadmalal, Barranca de los Lobos, etc.) and La Pampa provinces (Zetti, 1972; Cerdeño and Bond, 1998).

The smaller species, Paedotherium minor, is recognized in the Arroyo Chasicó Formation (Vivero and Las Barrancas members) and the Epecuén Formation, which represent the late Miocene Chasicoan and Huayquerian ages, respectively (Cerdeño and Bond, 1998). Contreras and Baraldo (2011) mentioned Paedotherium minor from horizons assigned to the Chasicoan and Huayquerian ages in San Juan province. Brandoni et al. (2012) mentioned the presence of Paedotherium minor in the El Degolladito, La Rioja province, from sediments of Salicas Formation. This species also is recognized from sediments of Cerro Azul Formation assigned to the late Huayquerian for Verzi and Montalvo (2008) (but see Prevosti and Pardiñas, 2009 for a discussion about age of these bearing sediments).

One of the largest species, Paedotherium typicum, is abundantly recorded in the Monte Hermoso (Monterhermosan age; Tomassini et al., 2013) and the Chapadmalal (Chapadmalalan age) formations in Buenos Aires province. It is coeval with P. bonaerense, but P. typicum occurs more frequently in the Montehermosan (Tomassini et al., 2013), while P. bonaerense is more abundant in the Chapadmalalan age. Some scarce remains indicate the persistence of P. typicum in the younger Marplatan levels of the Barranca de Los Lobos and Vorohué formations. Also this species has been mentioned from late Miocene Río Quinto Formation of San Luis province (Prado et al., 1998). Paedotherium cf. typicum also is recorded in the Pliocene Alvear Formation (Candela et al., 2007). The size of P. typicum and P. bonaerense is very similar (Table 1).

In a biostratigraphic context the last appearance of Paedotherium is in the Paractenomys chapadmalensis Zone (Marplatan Age, Sanandresian subage, late Pliocene, Cione and Tonni,1995). The probable persistence of Paedotherium in the Ensenadan age of Buenos Aires Province involves scarce remains assigned to P. bonaerense. Nevertheless, the stratigraphic provenance of these remains is doubtful (Bond et al., 1995).

Except for the records of Paedotherium minor in the late Miocene (Chasicoan-Huayquerian) from the Guandacay Formation in Bolivia (Marshall and Sempere, 1991), middle Miocene from Cura Mallín Formation in Chile (Wyss et al., 2003), and from the late Miocene of the Catamarca, Argentina (Valle del Cajón) and Paedotherium kakai in the late Miocene from Palo Pintado Formation, Salta in Argentina, the genus Paedotherium had a strictly middle latitude Pampean distribution. This contrasts with most high- and middle-latitude faunas (i.e., those south of 23°S) in which Paedotherium account for the majority or entirety of hegetotheriid remains (e.g., Sinclair, 1909; Zetti, 1972; Cerdeño and Bond, 1998). Paedotherium kakai is the first unambiguous record of the genus in the Eastern Cordillera NW of Argentina. At Quebrada Peñas Blancas, the Palo Pintado Formation (i.e., fluvial association; Fig. 5) ranges in age between 10.29±0.11 Ma and 5.27±0.28 Ma (Galli et al., 2011; Carrapa et al., 2006). Additionally, interfingering of this Palo Pintado Fm. with the Guanaco Formation at La Viña area (Sierra de Los Colorados, a laterally equivalent facies) has been dated at 8.73±0.25 Ma by K/Ar on biotite from an ash (Del Papa et al., 1993) and by zircon U-Pb at 9.31±0.31 Ma (Hain et al., 2011).

The Quebrada Peñas Blancas specimen was collected from near the top of the middle part of the Palo Pintado Formation (i.e., fluvial association), suggesting an age slightly older than 6 Ma and younger than 10 Ma. Magnetostratigraphic study in progress of the Palo Pintado Formation has dated the mammal-bearing horizon at ca. 8.8 Ma (late Miocene, personal communication, C. Galli, 2013).

 

Fig. 5. Schematic topographic profiles showing the paleoenvironment distribution (modified from Starck and Anzótegui, 2001). A. Present day; B. late Miocene (deposition time for the upper section of the Palo Pintado Fm.).

 

5.2. Hypsodonty of P. kakai and the paleoenvironment of the Valle Calchaquí in the late Miocene

The Pachyrukhinae are small terrestrial herbivorous hegetotheriids easily recognized by their specialized anterior dentition, ‘rabbit-like’ and ever-growing (rootless) incisors and cheek teeth. They were extremely abundant in the mid-Cenozoic of Argentina. Based on dental dimensions, their body mass would have ranged from about 1.8 to 2.2 kg (Castro, 2001; Elisamburu, 2011; Cassini et al., 2011); it is interesting to note that the only extant ungulate with similar size is the ruminant Asian tragulid mouse deer, the smallest artiodactyl known. Pachyrukhines are generally reconstructed as grassers and open habitat specialists that might have lived in burrows and resembled rabbits (leporids) or various South American rodents (caviids, chinchillids) in lifestyle (Sinclair, 1909; Kraglievich, 1926; Cifelli, 1985; Genise, 1989; Dozo, 1997; Cerdeño and Bond, 1998; Elissamburu, 2004).

The hypsodonty of Paedotherium kakai offers other possible paleoecological interpretation which is in agreement with the palaeoclimate and palaeonvironment inferred for the Palo Pintado Formation, characterized by habitats forested, with system of sinuous rivers, marsh and lagoons developed under a humid and subtropical climate, with short dry seasonality (Galli et al., 2011; Anzótegui and Horn, 2011) (Fig. 5). Study of megaflora of Palo Pintado indicate four paleocommunities: fresh water, marsh (e.g., Blechnum serrulatiformis, Acrostichum paleoaureum), riparian (e.g., Cedrella fissiliformis, Sapium haematospermoides, Nectandra saltensis, Ficus tressensii in the arboreal stratum, and the climbing Ranunculodendron anzoteguiae) and xerophytic forests areas (Anzótegui and Horn, 2011), without evidence of development of grasslands or open savannas. So, open habits with predominant grass were not the environments dominant inferred for Palo Pintado Formation. Note that the case of Paedotherium kakai is in contrast with the majority of the late Miocene extinct South American ungulates, for which no information on the paleoenvironment conditions of its bearing-units is little or not available. In this context, we assume that hypsodonty in P. kakai is not a feature associated with grasser feeding habits and strictly open habits. Then, if unquestionably hypsodont indicates high rates of tooth wear (Fortelius, 1985), we must explore which are the abrasive factors that explain the relatively high rate of tooth wear in P. kakai (Table 2).

At least partially, hypsodonty is here interpreted as feature reelecting the evolutionary history of the group previously acquired in the Pachyrukhinae during late Oligocene in Patagonia, when extensive grasslands were certainly absent (Palasezzi and Barreda, 2012; Billet et al., 2009; Kay et al., 1999; Reguero et al., 2010; Strömberg et al., 2011). On the other hand, hypsodonty in P. kakai is understood as feature associated to abrasive particles consumption during feeding.

Janis (1988) concluded that hypsodonty alone could not be taken as evidence for grazing behavior in extinct ungulates and suggest that, although do not the only factor; the grit had an important role for hypsodonty. Likewise, other authors (e.g., Williams and Kay, 2001; Mendoza and Palmqvist, 2008; Damuth and Janis, 2011 and citations herein) indicated that soil ingestion in ungulates has a considerable explanatory power of hypsodonty, irrespective of the proportion of the grass in the diet.

In line with these ideas, soil consumption, including abrasive particles such as sand, dust, volcanic glass, etc., adhered to surface of food or accidentally ingested, could explain, at least partially, the high degree of hypsodonty in P. kakai. Examples of living ungulates indicate that hypsodonty and wear rates vary with levels of soil ingestion, but not entirely with proportion of grass in the diet (Damuth and Janis, 2011). Currently the pronghorn antelope (Antilocapra americana) is an examples of an hypsodont not grasser but mixed-feeding species, in which soil intake explains, at least as an important factor, the tooth wear (Damuth and Janis, 2011). On the other hand, among extant ungulates, these authors given examples of some populations of grazing or mixed-feeding species that live in rainforest regions (e.g., Bubalus mindorensis, buffalo, Syncerus caffer), where the grass is essentially absent.

Ungar et al. (1995) support the presence of hypsodont species in forested habits obtaining source of wear on dust particles found in the canopies of tropical dry forests and rainforests.

Therefore, soil consumption, including probably sand near of border of rivers or lagoons, or consumption of dust or abrasive particles of soil adhered to food surfaces in floodplains or riparian forest could have acted as wear tooth in Paedotherium kakai. Compared with Paedotherium typicum and P. minor, the lesser degree of hypsodonty and the absence of cement of P. kakai would be indicative of a lesser amount of abrasive particle in the diet. P. kakai must have had a relatively lesser rate of abrasive particle consumption, indicative of a diet (food?) not highly abrasive, perhaps because it was being foraged close to water and so more free of grit. A high hypsodonty and the presence of cementum in Paedotherim typicum and P. minor evidence an increasing dietary abrasion as consequence of the grasslands became more widely available in the more open habits of Pampean region. These features common to these species suggest that their feeding habits were influenced by Cenozoic climate and its impact on paleoenvironment and habitat structure.

As discussed above, Paedotherium kakai probably was a mixed feeder compared with P. minor and P. typicum, consuming a variable diet obtained close to the ground. In the context of hypsodont species, this ungulate was probably a wide ranging species that lived in gallery forests, being able to eat close to water bodies of a system river and lagoons that occurred in the foodplains developed under humid and subtropical climate.

Other hypsodont species, the giant rodent Eumegamys paranensis from the late Miocene of Argentina, adds to the examples of hypsodont but not grasser species (Candela et al., 2013) dwellers of forested habits, developed under warm and humid climate, where the grasses were not predominant.

Acknowledgements
Research for this study was supported by Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT, PICT 2191 to AMC), CONICET-PIP No. 2010-2012, No. 11220090100-298), UNJu (SECTER N° 08/E033), UNSa (CI-UNSa N°1858). The authors would like to thank to J.N. Gelfo (Universidad Nacional de La Plata) and an anonymous reviewer for constructive criticism.

 

References

Ameghino, F. 1894. Enumération synoptique de espèces de mammifères fossiles des formations éocènes de Patagonie. Boletín de la Academia Nacional de Ciencias de Córdoba 13: 259-445.

 

Anzótegui, L.M. 1998. Hojas de Angiospermas de la Formación Palo Pintado, Mioceno superior, Salta, Argentina, Parte I: Anacardiaceae, Lauraceae y Moraceae. Ameghiniana 35 (1): 25-32.

 

Anzótegui, L.M.; Horn, M. 2011. Megaflora of the Palo Pin-tado Formation (Late Miocene) Salta, Argentina. Parte II. Revista Brasileira de Paleontologia 14 (3): 239-254.

 

Billet, G.; Patterson, B.; de Muizon, C. 2009. Craniodental anatomy of late Oligocene archaeohyracids (Notoungulata, Mammalia) from Bolivia and Argentina and newphylogenetic hypotheses. Zoological Journal of the Linnean Society 155: 458-509.

 

Bond, M.; Cerdeño, E.; López, G. 1995. Los ungulados nativos de América del Sur. In Evolución biológica y climática de la región pampeana durante los últimos cinco millones de años (Alberdi, M.T.; Leone, G.; Tonni, E.P.; editors). Monografías del Museo Nacional de Ciencias Naturales, CSIC (Consejo Superior de Investigaciones Científicas): 259-275. Madrid.

 

Brandoni, D.; Schmidt, G.I.; Candela, A.M.; Noriega, J.I.; Brunetto, E.; Fiorelli, L.E. 2012. Mammals from the Salicas Formation (late Miocene), La Rioja Province, northwestern Argentina: paleobiogeography, age, and paleoenvironment. Ameghiniana 49 (3): 375-387.

 

Burmeister, G. 1888. Relación de un viaje a la Gobernación de Chubut. Anales del Museo Nacional de Buenos Aires 3: 175-252.

 

Bywater-Reyes, S.; Carrapa, B.; Clementz, M.; Schoenbohm, L. 2010. The effect of late Cenozoic aridification on sedimentation in the Eastern Cordillera of NW Argentina (Angastaco Basin). Geology 38: 235-238.

 

Candela, A.M.; Noriega, J.I.; Reguero, M.A. 2007. The first Pliocene mammals from the Northeast (Mesopotamia) of Argentina: Its biostratigraphic and paleoenvironmental significance. Journal of Vertebrate Paleontology 27 (2): 476-483.

 

Candela, A.M.; Cassini, G.; Nasif, N. 2013. Fractal dimension and cheek teeth crown complexity in the giant rodent Eumegamys paranensis. Lethaia 46: 369-377. doi: 10.1111/let.12015.

 

Carrapa, B.; Strecker, M.R.; Sobel, E.R. 2006. Cenozoic orogenic growth in the Central Andes: Evidence from sedimentary rock provenance and apatite fission track thermochronology in the Fiambalá Basin, southernmost Puna Plateau margin (NW Argentina). Earth and Planetary Science Letters 247 (1): 82-100.

 

Carrera, N.; Muñoz, J.A. 2008. Thrusting evolution in the southern Cordillera Oriental (northern Argentine Andes): Constraints from growth strata. Tectonophysics 459: 107-122. doi: 10.1016/j.tecto.2007.11.068.

 

Cassini, G.H.; Vizcaíno, S.F.; Bargo, S.M. 2011. Body mass estimation in Early Miocene native South American ungulates: a predictive equation based on 3D landmarks. Journal of Zoology 287: 53-64.

 

Castro, P. 2001. Los Hegetotheriidae (Mammalia: †Notoungulata: Hegetotheria) del Paleógeno de Patagonia, Argentina: sistemática, filogenia y paleoecología. Tesis licenciatura (Unpublished) Universidad Nacional de Patagonia ‘San Juan Bosco’: 1-110. Chubut.

 

Cerdeño, E.; Bond, M. 1998. Taxonomic revision and phylogeny of Paedotherium and Tremacyllus (Pachyrukhinae, Hegetotheriidae, Notoungulata) from the late Miocene to Pleistocene of Argentina. Journal of Vertebrate Paleontology 18: 799-811.

 

Cifelli, R.L. 1985. South American ungulate evolution and extinction. The great American biotic interchange. In The Great American Biotic Interchange (Stehli, F.G.; Webb, S.D.; editors), Plenum Pres: 249-266. New York.

 

Cifelli, R.L. 1993. The phylogeny of the native South American ungulates, In Mammal Phylogeny (Szalay, F.S.; Novacek, M.J.; McKenna, M.C.; editors), Springer-Verlag: 195-216. New York.

 

Cione, A.L.; Tonni, E.P. 1995. Chronostratigraphy and ‘Land-mammal Ages’ in the Cenozoic of southern South America: principles, practices, and the ‘Uquian’ problem. Journal of Paleontology 69: 135-159.

 

Contreras, V.H.; Baraldo, J.A. 2011. Calibration of the Chasicoan-Huayquerian stages boundary (Neogene), San Juan, western Argentina. In Cenozoic geology of the Central Andes of Argentina (Salfity, J.A.; Marquillas, R.A.; editors). Instituto del Cenozoico, Universidad Nacional de Salta: p. 111. Salta.

 

Coutand, I.; Carrapa, B.; Deeken, A.; Schmitt, A.K.; Sobel, E.; Strecker, M.R. 2006. Orogenic plateau formation and lateral growth of compressional basins and ranges: Insights from sandstone petrography and detrital apatite fission-track thermochronology in the Angastaco Basin, NW Argentina. Basin Research 18: 1-26. doi: 10.1111/j.1365-2117.2006.00283.x.

 

Croft, D.A.; Anaya, F. 2006. A new middle Miocene hegetotheriid (Notoungulata: Typotheria) and a phylogeny of the Hegetotheriidae. Journal of Vertebrate Paleontology 26: 387-399.

 

Croft, D.A.; Flynn, J.J.; Wyss, A. 2004. Notoungulata and Litopterna of the early Miocene Chucal Fauna, northern Chile. Fieldiana: Geology (New Series) 50: 1-52.

 

Damuth, J.; Janis, C.M. 2011. On the relationship between hypsodonty and feeding ecology in ungulate mammals, and its utility in palaeoecology. Biological Reviews 86 (3): 733-758.

 

Davis, R.A. Jr. 1983. Depositional systems: A genetic approach to sedimentary geology. Prentice-Hall: 669 p. Englewood Cliffs, New Jersey.

 

De la Sota, E.R. 1972. Sinopsis de las Pteridofitas del Noroeste de Argentina, I. Darwiniana 17:11-103.

 

Del Papa, C.; Disalvo, A.; Reynolds, J.; Pereyra, R.; Viramonte, J. 1993. Utilización de niveles piroclásticos en correlación estratigráfica: un ejemplo para el Terciario superior del noroeste argentino. In Congreso Geológico Argentino, No. 12 y Congreso de Exploración de Hidrocarburos, No. 2, Actas II: 166-171. Mendoza.

 

Díaz, J.I.; Malizzia, D.C. 1983. Estudio geológico y sedimentológico del Terciario Superior del valle Calchaquí (departamento de San Carlos, provincia de Salta). Bulletin of Sedimentology 2: 8-28.

 

Dozo, M.T. 1997. Paleoneurología de Dolicavia minuscula (Rodentia, Caviidae) y Paedotherium insigne (Notoungulata, Hegetotheriidae) del Plioceno de Buenos Aires, Argentina. Ameghiniana 34: 427-435.

 

Elissamburu, A. 2004. Morphometric and morphofunctional analysis of the appendicular skeleton of Paedotherium (Mammalia, Notoungulata). Ameghiniana 41: 363-380.

 

Elissamburu, A. 2011. Estimación de la masa corporal en géneros del Orden Notoungulata. Estudios Geológios 68 (1): 91-111. doi: 10.3989/egeol.40336.133.

 

Flynn, J.J.; Novacek, M.J., Dodson, H.E.; Frassinetti, D.; McKenna, M.; Norell, M.A.; Sears, K.E.; Swisher, C.C.; Wyss, A.R. 2002. A new fossil mammal assemblage from the southern Chilean Andes: implications for geology, geochronology, and tectonics. Journal of South American Earth Sciences 15: 285-302.

 

Fortelius, M. 1985. Ungulate cheek teeth: developmental, functional, and evolutionary interrelations. Acta Zoologica Fennica 180: 1 76.

 

Galli, C.I.; Ramírez, A.; Barrientos, C.; Reynolds, J.; Viramonte, J.G.; Idleman, B. 2008. Estudio de proveniencia de los depósitos del Grupo Payogastilla (Mioceno Medio-Superior) aflorantes en el río Calchaquí, provincia de Salta, Argentina. In Congreso Geológico Argentino, No. 17, Actas 1: 353-354. Jujuy.

 

Galli, C.I.; Anzotegui, L.M.; Horn, M.Y.; Morton, L.S. 2011. Paleoambiente y paleocomunidades de la Formación Palo Pintado (Mioceno-Plioceno), Provincia de Salta, Argentina. Revista Mexicana de Ciencias Geológicas 28: 161-174.

 

Genise, J.F. 1989. Las cuevas con Actenomys (Rodentia, Octodontidae) de la Formación Chapadmalal (Plioceno superior) de Mar del Plata y Miramar (provincia de Buenos Aires). Ameghiniana 26: 33-42.

 

Hain, M.P.; Strecker, M.R.; Bookhagen, B.; Alonso, R.N.; Pingel, H.; Schmitt, A.K. 2011. Neogene to Quaternary broken foreland formation and sedimentation dynamics in the Andes of NW Argentina (25°S). Tectonics 30 (2): TC2006. doi: 10.1029/2010TC002703.

 

Janis, C.M. 1988. Estimation of tooth volume and hypsodonty indices in ungulate mammals, and the correlation of these factors with dietary preference. Muséum national d’Histoire naturelle Memoir série C53: 367-387.

 

Jordan, T.E.; Alonso, R.N. 1987. Cenozoic stratigraphy and basin tectonics of the Andes Mountains, 20°-28° south latitude. American Association of Petroleum Geologists Bulletin 71:49-64.

 

Kay, R.; Madden, R.H.; Vucetich, M.G.; Carlini, A.A.; Mazzoni, M.M.; Re, G.H.; Heizler, M.; Sandeman, H. 1999. Revised geochronology of the Casamayoran South American Land Mammal Age: climatic and biotic implications. Proceedings of the National Academy of Sciences of the United States of America 96: 13235-13240.

 

Kraglievich, L. 1926. Sobre el conducto humeral en las vizcachas y paquirucos Chapadmalenses con descripción del Paedotherium imperforatum. Anales del Museo Nacional de Historia Natural ‘Bernardino Rivadavia’ 34: 45-88.

 

Kraglievich, L. 1934. La antigüedad pliocena de las faunas de Monte Hermoso, deducidas de su comparación con las que le precedieron y sucedieron. El Siglo Ilustrado: 1 136. Montevideo.

 

Linnaeus, C. 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Editio Decima, Reformata, Holmiæ, Imprensis Direct, Laurentii Salvii, Tomus I.

 

Loomis, F.B. 1914. The Deseado Formation of Patagonia. Rumford Press: 1 232 p. Concord.

 

Marshall, L.G.; Sempere, T. 1991. The Eocene to Pleistocene vertebrates of Bolivia and their stratigraphic context: a review. In Fósiles y Facies de Bolivia (Suárez-Soruco, R.; editor). Yacimientos Petrolíferos Fiscales Bolivianos 1: 631-652. Santa Cruz.

 

Marshall, L.G.; Hoffstetter, R.; Pascual, R. 1983. Mammals and stratigraphy: geochronology of the continental mammal-bearing Tertiary of South America. Palaeovertebrata, Special Volume 93: 1-93.

 

Mendoza, M.; Palmqvist, P. 2008. Hypsodonty in ungulates: an adaptation for grass consumption or for foraging in open habitat? Journal of Zoology 274 (2): 134-142.

 

Miall, A.D. 1996. The geology of fluvial deposits. Springer Verlag: 582 p. Berlin.

 

Palazzesi, L.; Barreda, V. 2012. Fossil pollen records reveal a late rise of open-habitat ecosystems in Patagonia. Nature communications 3: p. 1294.

 

Pascual, R.; Vucetich, M.G.; Scillato-Yané, G.J.; Bond, M. 1985. Main pathways of mammal diversification in South America. In The Great American Biotic Interchange (Webb, F.G.S. a. S.D.; editor). Plenum Press: 219-247. New York.

 

Patterson, B.; Pascual, R. 1972. The fossil mammal fauna of South America. In Evolution, Mammals, and Southern Continents (Keast, A.; Erk, F.C.; Glass, B.; editors). State University of New York Press: 247-309. Albany.

 

Prado, J.L.; Chiesa, J.; Tognelli, G.; Cerdeño, E.; Strasser, E. 1998. Los mamíferos de la Formación Río Quinto (Plioceno), provincia de San Luis (Argentina). Aspectos bioestratigráficos, zoogeográficos y paleoambientales. Estudios Geológicos 54: 153-160.

 

Prevosti, F.J.; Pardiñas, U.F.J. 2009. Comment on The oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora): Late Miocene faunal turnover in central Argentina and the Great American Biotic Interchange’ by D.H. Verzi and C.I. Montalvo. Palaeogeography, Palaeoclimatology, Palaeoecology 267 (2008): 284-291. Palaeogeography, Palaeocli-matology, Palaeoecology 280: 543-547.

 

Reguero, M.A.; Castro, P.V. 2004. Un nuevo Trachytheriinae (Mammalia, Notoungulata, Mesotheriidae) del Deseadense (Oligoceno tardío) de Cabeza Blanca, Chubut, Argentina. Importancia bioestratigráfica y filogenética del género Trachytherus. Revista Geológica de Chile 31 (1): 45-64. doi: 10.5027/andgeoV31n1-a03.

 

Reguero, M.A.; Prevosti, F.J. 2010. Rodent-like notoun-gulates (Typotheria) from Gran Barranca, Chubut Province, Argentina. In The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia (Madden, R.; Carlini, A.A.; Vucetich, M.G.; Kay, R.; editors). Cambridge University Press: 152-169. New York.

 

Reguero, M.A.; Candela, A.M. 2011. Late Cenozoic mammals from the Northwest of Argentina: biochronological and biogeographical problems and perspective. In Cenozoic Geology of the Central Andes of Argentina (Salfity, J.A.; Marquillas, R.A.; editors). Instituto del Cenozoico, Universidad de Salta: 411-426. Salta.

 

Reguero, M.A.; Dozo, M.T.; Cerdeño, E. 2007a. Medistylus dorsatus (Ameghino, 1903), an enigmatic Pachyrukhinae (Hegetotheriidae, Notoungulata) from the Deseadan of the Chubut province, Argentina. Systematic and paleoecology. Journal of Paleontology 81 (6): 1301-1307.

 

Reguero, M.A.; Candela, A.M.; Alonso, R.N. 2007b. Biochronology and biostratigraphy of the ‘Uquian’ mammals (Pliocene-Early Pleistocene, NW of Argentina) and their significance in the Great American Biotic Interchange. Journal of South American Earth Sciences 23: 1-16.

 

Reguero, M.A.; Candela, A.M.; Cassini, G. 2010. Hypsodonty and Body Size in rodent-like notoungulates. In The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia (Madden, R.; Carlini, A.A.; Vucetich, M.G.; Kay, R.; editors). Cambridge University Press: 362-371. New York.

 

Riggs, E.S.; Patterson, B. 1939. Stratigraphy of late Miocene and Pliocene deposits of the Province of Catamarca (Argentina) with notes on the fauna. Physis 14: 143-162.

 

Roth, S. 1903. Los ungulados sudamericanos. Anales del Museo La Plata 5: 1 36.

 

Simpson, G.G. 1945. The principles of classification and a classification of mammals. Bulletin of the American Museum of Natural History 85: 1 350.

 

Simpson, G.G. 1980. Splendid Isolation, the Curious History of South American Mammals. Yale University Press: 266 p. New Haven.

 

Sinclair, W.J. 1909. Mammalia of the Santa Cruz Beds. In Reports of the Princeton University Expeditions to Patagonia, 1896-1899 (Scott, W.B.; editor). Princeton University, E. Schweizerbart’sche Verlagshandlung (E. Nägele). Paleontology 6, Typotheria 1: 1-110.Stuttgart.

 

Starck, D.; Vergani, G. 1996. Desarrollo tecto-sedimentario del Cenozoico en el sur de la Provincia de Salta-Argentina. In Congreso Geológico Argentino, No. 13, Actas 1: 433-452. Buenos Aires.

 

Starck, D.; Anzótegui, L.M. 2001. The late Miocene climatic change-Persistence of a climatic signal through the orogenic stratigraphic record in northwestern Argentina. Journal of South American Earth Sciences 14: 763-774.

 

Strömberg, C.A. 2011. Evolution of grasses and grassland ecosystems. Annual Review of Earth and Planetary Sciences 39: 517-544.

 

Tomassini, R.L.; Montalvo, C.I.; Deschamps, C.M.; Manera, T. 2013. Biostratigraphy and biochronology of the Monte Hermoso Formation (early Pliocene) at its type locality, Buenos Aires Province, Argentina. Journal of South American Earth Sciences 48: 31-42.

 

Ungar, P.S.; Teaford, M.F.; Glander, K.E.; Pastor, R.F. 1995. Dust accumulation in the canopy: a potential cause of dental microwear in primates. American Journal of Physical Anthropology 97 (2): 93-99.

 

Verzi, D.H.; Montalvo, C.I. 2008. The oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora): Late Miocene faunal turnover in central Argentina and the Great American Biotic Interchange. Palaeogeography, Palaeoclimatology, Palaeoecology 267 (3): 284-291.

 

Williams, H.S.H.; Kay, R. 2001. A comparative test of adaptive explanations for hypsodonty in ungulates and rodents. Journal of Mammalian Evolution 8: 207-229.

 

Wyss, A.R.; Charrier, R.; Croft, D.A.; Flynn, J.J.; Wertheim, J.A. 2003. New middle Cenozoic mammals from the Laguna del Laja region (Cura-Mallín Formation, south central Chile). Journal of Vertebrate Paleonto-logy 23: p. 113A.

 

Zetti, J. 1972. Observaciones sobre los Pachyrukhinae (Notoungulata) del Plioceno argentino. Importancia estratigráfica y paleobiogeográfica. Publicaciones del Museo Municipal de Ciencias Naturales de Mar del Plata 2 (2): 41 51.

 

Zittel, K.A. Von. 1893. Handbuch der Palaeontologie. Abteilung I. Palaeozoologie. Band IV, Vertebrata (Mammalia). Munich, R. Oldenbourg 11: 799 p.