Journal of Systematic Palaeontology, 2014 Vol. 12, Issue 5, 549–564, http://dx.doi.org/10.1080/14772019.2013.799611 A unique, Late Oligocene shrew-like marsupial from western Argentina and the evolution of dental morphology Analı́a M. Forasiepia∗, Francisco J. Goinb, M. Alejandra Abellob and Esperanza Cerdeñoa aCONICET, IANIGLA, CCT-Mendoza, Mendoza, Mendoza Province, Argentina; bCONICET, Museo de La Plata, La Plata, Buenos Aires Province, Argentina (Received 21 August 2012; accepted 21 January 2013; first published online 18 July 2013) We describe a new metatherian mammal, Fieratherium sorex gen. et sp. nov., found in western Argentina (Quebrada Fiera locality, southern Mendoza Province), in Late Oligocene deposits (Agua de la Piedra Formation, Deseadan age). The only known specimen is a juvenile with fragments of both dentaries, the right maxilla and a fragment of the left premaxilla with dentition. The loci and the number teeth preserved suggest a dental formula of I?3/i3, C1/c1, P3/p3, M?3/m?3. Fieratherium sorex has a convergent shrew-like appearance and a unique combination of features among metatherians and other South American mammals of Palaeogene age, including the well-known faunas of Patagonia. An analysis of its phylogenetic affinities suggests that Fieratherium is the sister-group of the Paucituberculata. As already described by other authors for several mammalian taxa, the mainly Patagonian South American Palaeogene fossil record offers little information to understanding the evolution of northern lineages. Fieratherium may represent a taxon belonging to a lineage that had its origin in Neotropical regions, so far unrecorded in the southern region of South America. http://zoobank.org/urn:lsid:zoobank.org:pub:5F6D3A50-6345-4E66-BE3E-7FEF6CC66A9B Keywords: Dentition; phylogeny; Mammalia; Metatheria; Cenozoic; South America Introduction Interpreting the evolution of the South American mammalian associations during the Palaeogene was classi- cally based on data collected from the southern tip of the continent (i.e. Patagonia; e.g. Simpson 1980; Madden et al. 2010; Vizcaı́no et al. 2012). These data have been comple- mented with recent fieldwork and further studies in the northern part of the continent (e.g. Kay et al. 1997; Cozzuol 2006; Croft 2007; Latrubesse et al. 2010; Sánchez Villagra et al. 2010) and mostly in Neogene strata. Distinct from both of these areas, Mendoza province, western Argentina, is just north of Patagonia and was the source of the extremely specialized marsupial Groeberia minoprioi (Polydolop- imorphia, Argyrolagoidea). George G. Simpson (1970) suggested that this species, as well as other peculiar forms, evolved from lineages that were absent in the best-known fossiliferous regions of Patagonia. In fact, several decades later, Goin & Candela (2004) described, from the intertrop- ical lowlands of western Amazonia (Peru), a new Palaeo- gene marsupial with primitive molar features that predict the pattern of groeberiids. This could indicate that the trop- ics were the source of some mammalian lineages that later spread into more marginal lands (e.g. Antoine et al. 2011). ∗Corresponding author. Email: borhyaena@hotmail.com This article was originally published with errors. This version has been corrected. Please see erratum http://dx.doi.org/10.1080/ 14772019.2013.830855 The palaeontological site of Quebrada Fiera is located in southern Mendoza Province, western Argentina (Fig. 1A), and has been known since the 1970s (Gorroño et al. 1979). Preliminary studies on the originally recovered fauna led to it being assigned to the Deseadan South American Land Mammal Age (SALMA), Late Oligocene (Pascual et al. 1965; Pascual & Odreman Rivas 1973). Due to the difficult access (Fig. 1B), the site was not prospected for several decades. However, since 2006 new fossil collections have been made during a series of field seasons (Prámparo et al. 2006; Cerdeño & Vera 2007; Cerdeño 2011). Currently, fossils known from this locality include phorusrhacids, indeterminate small birds, and numerous remains belong- ing to several mammalian lineages, many of which are still under description: xenarthrans (sloths, glyptodonts and armadillos), native ungulates (notohippids, archaeo- hyracids, interatheriids, hegetotheriids, toxodontids, leon- tiniids, homalodotheriids, litopterns and pyrotheres), a rodent, and metatherians (Bond & Pascual 1983; Gorroño et al. 1979; Vera & Cerdeño 2009; Cerdeño & Vera 2010; Cerdeño et al. 2010; Cerdeño 2011). Metatherians are known from three specimens belonging to three different taxa: two are the carnivorous sparassodonts Proborhyaena gigantea (Proborhyaenidae; Bond & Pascual 1983) and C© 2013 Natural History Museum D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 http://dx.doi.org/10.1080/14772019.2013.799611 http://zoobank.org/urn:lsid:zoobank.org:pub:5F6D3A50-6345-4E66-BE3E-7FEF6CC66A9B http://dx.doi.org/10.1080/14772019.2013.830855 http://dx.doi.org/10.1080/14772019.2013.830855 550 A.M. Forasiepi et al. Figure 1. Geographical and stratigraphical occurrence of Fieratherium sorex gen. et sp. nov. (MCNAM-PV 3958). A, location of the Quebrada Fiera fossil site in the south of Mendoza Province, Argentina; B, photograph of the site; the numbers correspond to the lithostratigraphical units mentioned in C; the arrow indicates the place of finding; C, stratigraphical column exposed at Quebrada Fiera; the marsupial Fieratherium sorex gen. et sp. nov. comes from the upper levels exposed on the site of the Agua de la Piedra Formation (Late Oligocene; Deseadan SALMA). The life reconstruction of F. sorex was created by Jorge Blanco. D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 Late Oligocene shrew-like marsupial 551 Table 1. Measurements (mm) of Fieratherium sorex gen. et sp. nov. (MCNAM-PV 3958) from the Late Oligocene (Deseadan age) of Quebrada Fiera, Mendoza, Argentina. P2 DP3 M1 M3 p1 p2 dp3 m1 Length 1.36 1.26 2.66 3.49 1.00 1.20 1.11 2.33 Maximum width 0.73 1.10 2.33 3.02 0.81 0.93 0.66 1.40 (tr) 1.33 (tal) Abbreviations: tal, talonid; tr, trigonid. Pharsophorus sp. (Borhyaenidae; Cerdeño 2011), and the third is the subject of this paper. Here we describe a new and peculiar metatherian from Quebrada Fiera. The very tiny specimen (Table 1) was discovered while preparing the large dentary of a notoungulate in the laboratory. The scope of this work is to describe the new taxon, examine its phylogenetic affinities, and infer dietary habits. The new mammal adds signifi- cant information to the extensive Palaeogene diversity and adaptive radiation of the South American metatherians. Its uniqueness is suggestive of an evolutionary history for its lineage that probably occurred far north of Patagonia, in a different Neotropical context. Institutional abbreviation MCNAM-PV: Museo de Ciencias Naturales y Antropológicas ‘J. C. Moyano’, Vertebrate Paleontol- ogy Collection, Mendoza Province, Argentina. Anatomical abbreviations Capital and lower case letters, C/c, canine; I/i, incisor; P/p, premolar; M/m, molar, refer to upper and lower teeth, respectively; D/d refers to deciduous teeth (DP3/dp3). Geographical and stratigraphical location Quebrada Fiera is located about 15 km south of El Zampal, Malargüe Department, Mendoza Province, Argentina (Fig. 1A), at about 1400 m above sea level. The stratigraphi- cal sequence begins with the upper section of the Malargüe Group: the Loncoche and Roca formations (Campanian and Maastrichtian age, respectively), overlain by the early Palaeogene Pircala-Coihueco formations (Gorroño et al. 1979; Narciso et al. 2004; Combina & Nullo 2002). This sequence is affected by an erosive discordance and it is followed by 2–4 m of clastic conglomerates in a silty matrix: the Rodados Lustrosos (Spanish for ‘polished pebbles’; Groeber 1946). The Rodados Lustrosos are followed by about 40 m of sandstones, clays and tuffs, of whitish, grey- ish and light brown colour (Gorroño et al. 1979; Fig. 1C). The fossil vertebrates collected in the locality of Quebrada Fiera were unearthed from the upper levels exposed in the area, represented by the silty tuffs (Gorroño et al. 1979; Fig. 1B, C). The sedimentary sequence of Quebrada Fiera was originally considered as either part of the Complejo vulcano-sedimentario del Terciario Inferior (Gorroño et al. 1979) or the Complejo Efusivo Eógeno (Bettini 1982), but currently it is included in the Agua de la Piedra Formation (e.g. Narciso et al. 2004; Combina & Nullo 2008). The deposits of this unit represent an alluvial plain with low energy streams, influenced by strong volcanism (Narciso et al. 2004). The sequence of the Agua de la Piedra Forma- tion exposed at Quebrada Fiera represents the basal portions of the unit (Combina & Nullo 2008). The mammalian association suggests that it was deposited during the Late Oligocene (Deseadan age; Gorroño et al. 1979; Narciso et al. 2004). Systematic palaeontology Class Mammalia Linnaeus 1758 Subclass Metatheria Huxley 1880 Genus Fieratherium nov. Type species. Fieratherium sorex sp. nov. Diagnosis. As for the type and only known species. Derivation of name. Fiera- after Quebrada Fiera locality; -therium, from the Latin therion, beast, common ending of many mammal generic names. Fieratherium sorex sp. nov. (Figs 1C, 2, 3) Diagnosis. Differs from all other metatherians in the following combination of features: I2–I3 large and labi- olingually compressed; i1 hypertrophied and procumbent; reduced canines; p1 single-rooted; p2 with a low principal cusp; M1 with a hypocone-like talon in a basal position, short and wide anterior cingulum, tall and well-defined parastyle, large StB posteriorly placed, narrow paracone, absence of premetacrista and incomplete postparacrista; M3 labially reduced with paracone taller than metacone and wider protocone compared with M1; lower molars with extremely reduced paraconid, low metaconid located close to the protoconid, m1 with spire-like entoconid, circular in cross-section and located at the posterior border of the talonid, hypoconulid absent. Derivation of name. The specific epithet sorex, is the Latin meaning for ‘shrew’, in reference to the shrew-like appear- ance of the new species. D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 552 A.M. Forasiepi et al. Figure 2. Fieratherium sorex gen. et sp. nov. (MCNAM-PV 3958) from Quebrada Fiera, Mendoza, Argentina; Deseadan age, Late Oligocene. A, fragment of left premaxilla with i1–i3 in lateral and ventral views; arrow indicates the anterior border of the incisive foramen; B, right maxilla in occlusal view with P2, DP3, M1, crypta of M2 and M3; C, detail of P2, DP3 and M1 in occluso-lingual, labial and lingual views; D, detail of M3 in occlusal and occluso-lingual views. Holotype. MCNAM-PV 3958, fragments of both dentaries, right maxilla and fragment of left premaxilla with dentition partially preserved, all belonging to the same, juvenile specimen (Figs 1C, 2, 3). Occurrence. Quebrada Fiera (36◦33′13.3′′S, 69◦42′3.5′′W; Fig. 1A), Malargüe Department, south- ern Mendoza Province, Argentina, from the Agua de la Piedra Formation, Late Oligocene (Deseadan SALMA). Description. MCNAM-PV 3958 is recognized as a juve- nile specimen (sensu Anders et al. 2011) because of the presence of deciduous teeth (DP3 and dp3), the near absence of wear on the occlusal surface of the teeth, and the early erupting condition shown by several molars. Left M1 and m1–m2 have their crown bases slightly below the alveolar plane and open alveoli, indicating an incomplete eruption. Left M3 is partially erupted with more than three- quarters of the crown already out of its crypt. The right dentary has the dental crypt, but not the m3, indicating that this molar was still in the process of erupting. Premaxilla. Part of the palatal and facial portions of a left premaxilla have been preserved (Fig. 2A). In ventral view and lingual to the first two incisors, the anterior portion of the left incisor foramen is observed, which is quite small compared with other shrew-like marsupials (e.g. caenolestids). In lateral view, the bone is slightly convex at the level of the root of I1 and appears to be quite high, which is an unusual feature in most marsupials. Maxilla. The palatal portion of the right maxilla is the best preserved part of the specimen. The palate is wide D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 Late Oligocene shrew-like marsupial 553 Figure 3. Fieratherium sorex gen. et sp. nov. (MCNAM-PV 3958) from Quebrada Fiera, Mendoza, Argentina; Deseadan age, Late Oligocene. A, right dentary with i1–i3, p2, and dp3 in occlusal view; B, left dentary with i1, p1, p2, dp3, m1 and trigonid of m2 in occlusal, labial and lingual views; C, same dentary in anterior and posterior views. at the level of molars, narrowing at the level of DP3 (Fig. 2B). Small vascular foramina open next to the tooth alveoli. It is not possible to assess if palatal vacuities were present, though as with many living marsupials with palatal vacuities, there is a shallow groove anterior and lingual to M1, continuing to a point lingual to the alveolus of P1. Dentary. Both dentaries are partially preserved (Fig. 3A, B). The horizontal ramus is slender and low, even lower than the m1; however, this condition is related to the juvenile stage of the specimen. The labial alveolar border of the dentary is slightly lower than that of the lingual. In lateral view, there are two mental foramina; the anterior is the largest and is located below p2, the second is below m1 (Fig. 3B). The symphysis is smooth and long, with the main axis almost horizontal, extending back to the level of dp3. Dental formula. There were no less than seven antemo- lar teeth in the upper and lower dentitions, as reconstructed D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 554 A.M. Forasiepi et al. from the preserved teeth, bones and alveoli. We conclude that the dental formula is best expressed as I?3/i3, C1/c1, P3/p3, M?3/m?3, according to the following analysis. Three upper incisors are present in the preserved premax- illa (Fig. 2A). Because the premaxilla is broken anteriorly and posteriorly, it is impossible to determine if there were additional incisors. The first incisor is distinctively shaped, compared with the remaining elements (see below), as occurs with the first incisor in many marsupials (e.g. didel- phimorphians; Voss & Jansa 2003). If this was also the case in Fieratherium, then the anteriormost preserved incisor is likely an I1. An isolated conical tooth is here referred to a right upper canine. Its position in the matrix is vertical and close to the maxilla with its tip pointing downwards with respect to this bone (Fig. 1C). The maxilla has two premo- lars (P2 and DP3) and an alveolus immediately anterior to P2 (Fig. 2B). Its shape does not match the coronal outline of the upper canine; so, we interpret it as the alveolus of P1. Finally, on the palatal portion of the maxilla, there are two molars (M1 and M3), and the alveoli for an intermediate element (M2). The bone is broken posterior to the M3, in such a way that it is impossible to confirm the existence of an M4. Also, the juvenile state of the material precludes an M4 having erupted, even if one is present in the adult. From these observations, we conclude an upper dental formula of I?3, C, P3, M?3. Our interpretation of the lower dental formula relies on the combined evidence from both dentaries (Fig. 3A, B). The anteriormost lower tooth is large and procumbent, and is interpreted as the first incisor (i1). It is followed by two small, single-rooted teeth (see the right dentary in Fig. 3A) identified as two additional incisors. Posterior to these, there is the alveolus for a single-rooted tooth identified as a lower canine (right dentary; Fig. 3A). Between this last alveolus and the first molar there are three teeth, here interpreted as p1, p2, and dp3; p2 and dp3 are preserved in both dentaries, whereas p1 is present in the left one (Fig. 3B). The right p1 was preserved detached from the dentary. The right mandible has no molars attached; the left one has the m1 and the trigonid of m2. There is no indication of the final number of molars, though there is the crypt for at least one additional molar posterior to m2 in the right dentary. We infer that the lower dental formula is: i3, c1, p3, m?3. Deciduous premolar. The molariform tooth that is set anterior to the first molar has a complex morphology, as in the deciduous tooth (DP3/dp3) of other metatherians (e.g. Voss & Jansa 2003). Both upper and lower molariform teeth imbricate between P2/p2 and M1/m1 (Figs 2C, 3B), suggesting that the molariform element erupted before the contiguous teeth. A computed tomography (CT) analysis performed on the maxilla revealed the presence of denser material than bone just below the molariform tooth, which most likely represents the P3 inside its crypt. Although the CT images obtained were low quality and inconclusive. The overall evidence leads us to conclude the molariform upper and lower teeth are deciduous elements. Upper teeth. The first incisor is styliform, stout, and slightly recumbent. The I2 and I3 are triangular in outline and strongly compressed labiolingually. There is a central cusp and a long anterior crest; the posterior crest is more vertical. I2 is larger than I3 (Fig. 2A). An isolated, single-rooted tooth is identified as a right canine (Fig. 1C). This tooth is short, slightly recumbent and conical at its apex, with a convex labial face and a more flattened lingual one. There is a plane surface at its posterolabial slope, near the crown base, which is probably a fracture. The alternative interpretation as a wear facet seems unlikely; the animal is young and the usual position for the facets in the upper canines is at the lingual side of the tooth. The teeth preserved in the maxilla are P2, DP3, M1 and M3 (Fig. 2B). The P2 is completely erupted. It has two roots with the anterior slightly smaller than the posterior. The tooth sits obliquely in the maxilla with the anterior root slightly labial and the posterior posterolingual to it. The crown consists of an asymmetrical main cusp followed by a broad posterior cingulum, which is wider lingually. There is a proportionally long crest running from the apex of the main cusp towards the posterior edge of the tooth. DP3 is small by comparison with M1 and has a complex crown morphology (Fig. 2B, C). It has three thin roots: two labial and one lingual. The antero-labial root is the smallest and the postero-labial is the largest. The crown is triangular in occlusal view and consists of three main cusps: para- cone, metacone and protocone, and two smaller: parastyle and metastyle. Paracone and metacone are twinned and the metacone is the tallest. Parastyle, metacone and metastyle are aligned. There is no stylar shelf; instead, the labial border of the tooth forms a vertical wall defined by the already mentioned labial cusps. The protocone is small and low, without a basin. There is a minute cusp just posterior and labial to the protocone and almost at the same horizon- tal plane. The M1 is proportionally large, high-crowned and triangular in outline (Fig. 2B, C). The metacone is the tallest cusp of the crown, closely followed by the StB. The paracone and the metacone are triangular in cross-section and with flat labial surfaces. In lingual view, feeble vertical enamel striations are developed on the metacone and protocone (Fig. 2C). The paracone and metacone are close to each other and the StB is wedged between: the lingual slope of the StB is positioned between the paracone and the metacone, in a place usually occupied by the centrocrista. The postparacrista is incomplete and ends at the lingual slope of StB, while the premetacrista is absent. Labial and basal to the metacone there is a small enamel ridge that connects this cusp with the StD. The preparacrista is short, D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 Late Oligocene shrew-like marsupial 555 almost vertical, and ends at the anterior slope of the StB. The postmetacrista is large and oblique to the transversal axis of the tooth. The stylar shelf is narrower at the anterior part of the tooth and widens posteriorly. It bears two main cusps, StB and StD. StB is tall and set labially and posterior to the paracone, almost at the middle of the anteroposterior length of the tooth. StD is smaller than StB and slightly labiolingually compressed. StB has one crest descending posteriorly from its apex, StD has two crests: one anterior and the other posterior to its apex. The anterior crest of StD meets the posterior crest of StB, while its posterior crest tends toward, but does not reach, the metastylar corner of the tooth. The parastylar corner projects forwards and bears a well-defined StA. This cusp is prominent, sharp; it is set lower than the remaining structures of the stylar shelf and, on the contrary, is associated to the anterobasal cingulum. This cingulum is short, broad and lingually oblique. The protocone is narrow and it is set in the crown lower than the paracone and metacone. Its labial face is almost vertical. The paraconule and the metaconule are absent; however, there are preprotoconal and postprotoconal crests slightly swollen and curved at their labial endings. A possible interpretation of this is that these swellings constitute vestiges of the conules. There is a broad posterointernal cusp developed at the base of the crown, much below and immediately behind the protocone (Fig. 2C). This cusp is taller at the lingual border, and descends to the labial border of the tooth. The M2 is not preserved. There are at least two alveoli, with the lingual one much larger than the postero- labial (Fig. 2B). The M3 is well-preserved except that its labial portion is broken (Fig. 2B, D). It is lower and almost half the size of M1. The M3 sits lingual to M1. This position may be post-mortem deformation, but it is placed just below a bony buttress separating the M2 and M3 loci. M3 differs from M1 in that the paracone is taller than the metacone. The paracone and the metacone are more distant from each other and there is a V-shaped centrocrista. The preparacrista is longer than that of the M1. The labial faces of the para- cone and metacone are flat. The postero-labial border of the tooth is broken; therefore, the length of the postmetacrista is unknown. The StB is lower and more rounded in section than in the M1. Behind the StB, there is a very small StD. The protocone is proportionally taller and broader, and the preprotoconal and postprotoconal crests are better defined. Other structures of this tooth are lost by fracture. Lower teeth. The first incisor is hypertrophied, procum- bent and slightly curved at its distal end (Fig. 3A, B). The tip is laterally compressed, while the rest of the crown is more cylindrical. In the broken left incisor it can be seen that the labial enamel layer is thicker than the lingual one (Fig. 3C). Where the labial and lingual enamel layers join, there is a sharp edge, which runs dorsally and over the whole length of the tooth. The alveolus of this tooth opens at the anterior end of the dentary. The second and third lower incisors are single-rooted and slightly procumbent (Fig. 3A). The crowns are wide posteriorly. The apices are laterally compressed. In lateral view, the crown of i2 is symmetrical and round, and the crown of i3 is asymmetrical with a longer posterior edge. The second lower incisor is slightly staggered over the i1 and a bony buttress of the dentary raises the labial alveolar base of the i2 above the alveolar base of i3. Because of this staggered condition this tooth is likely homologous to the i3 of other metatherians (following Hershkovitz 1982, 1995), but we refer to it as i2 based on its location. The buttress of the second lower incisor in Fieratherium is low and the staggered condition is subtly defined compared with most marsupials. Among them, the morphology of Fieratherium resembles living caenolestids: the procum- bent first lower incisor (the serially homologous i2) and the following incisors are not as crowded as in other metathe- rians, consequently, the i3 slightly staggers over the i2 (Hershkovitz 1995). The p1 is single-rooted and high (Fig. 3B). The crown widens posteriorly at its base; it has one main cusp which is labiolingually compressed. The p2 is double-rooted and slightly lower than p1. It is more obliquely set with respect to the anteroposterior axis of the dentary. The apex of the main cusp is laterally compressed, and its base is wider than p1. The dp3 has two slender roots and is small with a complex morphology (Fig. 3A, B). This tooth is proportion- ally smaller than the deciduous tooth of at least some living didelphids (Online Supplementary Material Appendix 1). There is a main cusp, the protoconid, followed posteriorly by a short, basined talonid. The paraconid and the meta- conid are absent, as well as the anterior cingulum. The protoconid is blunt and triangular in section. The prepro- tocristid is short and poorly defined; it descends towards the anterior end of the tooth. A blunt crest connects the apex of the protoconid with the hypoconid. The talonid is short, narrow and basined. There are two similarly sized, laterally compressed cusps, the entoconid (lingual) and the hypoconid (labial); the entoconid is placed posteriorly with respect to the hypoconid. There is no hypoconulid. There is also a short and oblique posthypocristid that directs towards the entoconid. The m1 is roughly rectangular in outline, with the trigo- nid higher and slightly wider than the talonid (Fig. 3B). The protoconid is the largest cusp, more than twice the size of the remaining trigonid cusps. The protoconid is triangular in cross-section, with a sharp preprotocristid descending anterior, almost parallel to the anteroposterior axis of the tooth. The paraconid is low, anteroposteriorly compressed, and located slightly laterally. The metaconid is small and twinned to the protoconid. The talonid is shorter than the trigonid. The talonid bears two cusps similar in height: the entoconid and hypoconid. The entoconid is columnar, spire- like, and circular in cross-section; it is located close to the D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 556 A.M. Forasiepi et al. posterior border of the tooth. There is no pre-entocristid. The hypoconid is triangular in cross-section. The cristid obliqua ends labial to a point below the metacristid notch. The posthypocristid descends medially towards the poste- rior base of the entoconid. The hypoconulid as such is absent; at the lingual end of the posthypocristid, there is a small swelling that could be interpreted as the vestige of this cusp. The presence of the anterior cingulum cannot be confirmed in m1. There is no posterior cingulum. The trigonid of m2 is the only structure preserved from this tooth (Fig. 3B, C). It is larger and the general morphol- ogy resembles the m1, differing in the proportionally larger paraconid and the more distant position of the metaconid with regard to the protoconid. There is a broad and short anterior cingulum. The metacristid notch is shallow. Discussion Phylogenetic analysis The phylogenetic position of Fieratherium sorex was tested by a cladistic analysis, using the data matrix of morpho- logical characters of Goin et al. (2009). Modifications were made according to the taxa analysed in the present study and new characters were added (Online Supple- mentary Material Appendices 2 and 3). The taxa scored include 17 metatherians represented by the crown-group Marsupialia (Paucituberculata, Microbiotheria and fossil relatives) and two basal stem marsupials considered as the outgroup (Alphadon and Pucadelphys). The selection of taxa is concentrated on ‘pseudodiprotodont’ marsupi- als. The matrix includes 44 morphological characters that describe the morphology of the dentary and the upper and lower dentition. Of the 44 characters selected, 30 are binary and 14 are multistate of which four are ordered (characters 2, 3, 30 and 38). An equally weighted parsimony analysis was conducted using TNT 1.1 (Goloboff et al. 2008). An exact search produced four most parsimonious trees of 111 steps (consis- tency index = 0.550; retention index = 0.702). The Bremer support is very low for each node, suggesting that the stabil- ity of the tree is weak. The strict consensus and its Bremer values are shown in Fig. 4. The general topology of the tree resembles the results in Goin et al. (2009). The most striking difference concerns the unresolved position of Pucadelphys and Derorhynchus. In two of the four trees obtained, Pucadelphys is located outside the group formed by the common ancestor of Micro- biotheria, Paucituberculata, and all of its descendants, in agreement with the majority of the analyses (e.g. Sánchez Villagra et al. 2007; Beck et al. 2008; Forasiepi 2009; Ladevèze & Muizon 2010). In the two remaining trees, Pucadelphys is closer to the Paucituberculata, similar to Goin et al. (2009). In this study and in Goin et al. (2009), it is probable that the limited taxon sample of the ‘pseu- dodiprotodont’ marsupials and the characters selected are affecting the resolution of the phylogenetic position of Pucadelphys. Derorhynchus is here found in an unresolved position or closer to the Paucituberculata, as in Goin et al. (2009). In an alternative hypothesis (Ladevèze & Muizon 2010), Derorhynchus is located outside the crown group Marsupialia. The phylogenetic position of these Palaeogene metatherians is pending further analysis. Fieratherium sorex is resolved in all the trees as a stem Paucituberculata. This clade is supported by two unambigu- ous synapomorphies: reduced or absent lower canine (char- acter 6 [1]) and reduced or absent hypoconulid (character 13 [1]). In addition Fieratherium shares with paucitubercu- latans the presence of three lower incisors, hypertrophied first lower incisor, large StB, reduction of M3, and lack of paraconules. Some features of the Fieratherium dentition resemble basal paucituberculatans, such as Evolestes and Bardalestes (Goin et al. 2007, 2009) in having StB and StD separated from the unreduced paracone and metacone, StB slightly posteriorly located, and a short and wide anterior cingulum (e.g. Evolestes; Goin et al. 2007). Bardalestes hunco and Evolestes hadrommatos are basal paucituberculatans. Bardalestes is known from Late Pale- ocene and Early-Middle Eocene levels (Itaboraian and Paso del Sapo fauna) of Patagonia and Evolestes from Oligocene levels (Deseadan) of Bolivia (Goin et al. 2007, 2009). According to the characters used in this study (Online Supplementary Material Appendix 2), Bardalestes shares with the remaining paucituberculatans three unambiguous synapomorphies: presence of pre-entocristid in m1–m3 (character 14 [0]), laterally compressed entoconid (char- acter 15 [1]), and StC fused to StD (character 41 [2]). Evolestes has two additional unambiguous synapomor- phies: absence of postcingulum (character 23 [1]) and very large metaconule, hypocone-like (character 38 [2]). These characters and other features classically used to support the paucituberculatan clade, such as a labially salient hypoconid, StB and StD larger than paracone and metacone, and winged and lingually expanded metaconule (Abello 2007; Goin et al. 2007, 2009; see also below) are absent in Fieratherium and hence exclude it from this group. In addition, Fieratherium has some uniquely derived features, such as M1 with a hypocone-like talon in a basal position, short and wide anterior cingulum separated from the stylar shelf, tall and well-defined parastyle, narrow para- cone, M3 with paracone taller than metacone; low meta- conid located close to the protoconid, spire-like entoconid, circular in cross-section and located at the posterior border of the talonid, that support the exclusion of Fieratherium from the Paucituberculata. The name Paucituberculata is maintained for the group that includes the most recent common ancestor of Riolestes, Bardalestes, the Palaeothen- toidea and Caenolestoidea clade, and all of its descendants (following Goin et al. 2009). D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 Late Oligocene shrew-like marsupial 557 Figure 4. Strict consensus cladogram (111 steps, consistency index = 0.550, retention index = 0.702) with unambiguous synapomorphies; black circles indicate autapomorphic features and white circles indicate homoplastic synapomorphies. Numbers at nodes indicate the Bremer support. The Paucituberculata is an endemic South Ameri- can clade of marsupials first recognized in the latest Paleocene–Early Eocene (Itaboraı́ and Las Flores forma- tions; Goin et al. 2009; see Gelfo et al. 2009 for a discus- sion of the age of the units). The radiation of the group took place in the Early Oligocene (pre-Deseadan ages) and early records are rare and sparse. During the Early Miocene (Colhuehuapian), paucituberculatans diversified with the record of 11 genera distributed into four different clades: Caenolestidae, Pichipilidae, Abderitidae and Palaeothenti- dae (Marshall 1980; Abello 2007; Abello & Rubilar Rogers 2012). The group declined during the late Neogene and is currently represented by Caenolestes, Lestoros and Rhync- holestes. The phylogenetic position of Fieratherium (Fig. 4) suggests that it represents a different lineage closely related to but placed outside the Paucituberculata. The discovery of Fieratherium reinforces the possibility that the diversity of the ‘pseudodiprotodont’ marsupials during the Cenozoic of South America was wider than previously thought and includes lineages whose early history remains unknown. Fieratherium shares some characters with basal marsupials, such as Derorhynchus and protodidelphids. Derorhynchus, similar to Fieratherium, has a low para- conid in m1, a talonid subequal in length to the trigonid, and a spire-like entoconid (Paula Couto 1952; Marshall 1987; Goin et al. 1999). In protodidelphids (e.g. Proto- didelphis and Guggenheimia; Paula Couto 1952; Marshall 1987), the upper molars have large StB slightly posteriorly located and large StD, and tall and spire-like-entoconid. In addition, these basal taxa have a postprotoconal cingulum, D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 558 A.M. Forasiepi et al. which would represent the homologous structure of the distolingual hypocone-like cusp of Fieratherium (see below). Derorhynchus is known since the Late Paleocene (Salamanca Formation; Bond et al. 1995), while proto- didelphids are known since the Early Eocene (Itaboraı́ and Las Flores formations; Goin et al. 1997). The similari- ties between Fieratherium and these early Palaeogene taxa, lacking in other known taxa from the well-studied Deseadan and Colhuehuapian localities from Patagonia and Bolivia, are worth mentioning. Comparisons with these Palaeo- gene taxa and the analysis of the phylogenetic position of Fieratherium allow interpretation of the evolution of char- acter states, such as the occurrence of the hypocone-like cusp in the M1. This cusp is absent from all other known metatherians. Upper molars: distolingual cusp The last common ancestor of eutherians and metathe- rians does not have a hypocone (e.g. Simpson 1936), but possesses a small metaconule. The metaconule is variably present in several successive therian sister taxa (e.g. Pappotherium, Falepetrus), some basal eutherians (e.g. Zalambdalestes, Kennalestes, Cimolestes, Didelpho- dus), and metatherians (e.g. Deltatheridium, Alphadon, Pediomys, Asiatherium). The hypocone was defined by Osborn (1888) as the posterointernal cusp of the upper molars that originates from an expansion of the postcingu- lum (Osborn 1897, 1907; see also Gregory 1934; Kielan- Jaworowska et al. 2004; Anemone et al. 2012). Later, a diverse origin for this cusp was accepted. Simpson (1936) and others concurred that the hypocone is formed by budding or fission on the protocone, overgrowth from the posterior cingulum, enlargement and displacement of the metaconule, or other evolutionary processes (see also Hunter & Jernvall 1995). Hence, the term hypocone was largely used in a topographic sense without considering the homology of its origin. In addition, an enlarged distolin- gual cusp was independently achieved among different mammalian lineages (e.g. Gregory 1934; Hunter & Jern- vall 1995; Anemone et al. 2012). In this phylogenetic context, the cusp generally called the hypocone is clearly not homologous between major taxonomic groups that possess the cusp (e.g. Simpson 1936; Van Valen 1994; Sánchez Villagra & Kay 1996). Among metatherians, paucituberculatans, polydolopi- morphians, peramelemorphians, and diprotodont marsupi- als have an enlarged distolingual cusp. The paucitubercu- latan cusp is considered homologous to the metaconule (Abello 2007; Goin et al. 2007; contra Marshall 1980) and also in Australian forms (e.g. Tedford & Woodburne 1987, 1998; contra Osborn 1907; Sánchez Villagra & Kay 1996; see below). Some diprotodonts (e.g. Pseudocheiridae, Phas- colarctidae, Ectopodontidae, among others) have, in addi- tion, a neomorph cusp at the lingual base of the metacone, the neometaconule (Woodburne et al. 1987a, b). Consider- ing the latter structure, accessory distolingual cusps among metatherians derive from different parts of the tooth and are not homologous among the lineages. Because of its uncer- tain origin, Sánchez Villagra & Kay (1996) suggested that the distolingual cusp be named based on its topography and function, in spite of its origin (see Tedford & Woodburne 1998 for an alternative view). Additionally, occlusion of the metaconule finishes at the end of Phase I of mastica- tion, when the cusp is located between the hypoconid of one molar and the protoconid of the next molar of the tooth row. The hypocone, in turn, occludes with the lingual side of the trigonid basin during Phase I and continues in active occlusion during Phase II of mastication (Sánchez Villagra & Kay 1996). The enlarged distolingual cusp of Fieratherium is not derived from the metaconule. If the swelling of the post- protoconal crest is the vestige of the metaconule, as we suggest in the description, then the distolingual cusp is derived from another tooth structure. The distolingual cusp of Fieratherium has no morphological relation with the occlusal surface of the protocone, and is located at the base of the crown, arguing in favour of an origin from the postprotoconal cingulum. This is present in some basal stem marsupials (e.g. Turgidodon; Johanson 1996) and in some Paleocene taxa, such as Protodidelphis and Guggen- heimia from Las Flores Formation (Goin et al. 1997, personal observations) which represent the sister taxa of Fieratherium and paucituberculatans (Fig. 4). Moreover, the distolingual cusp in Fieratherium does not occlude with any structure of the lower molars. In occlusion (Fig. 5), it is located between successive lower molars, and mostly at the lingual side of the talonid of the opposite molar. Hence, the distolingual cusp of Fieratherium has a different function to that of other metatherians. In summary, the distolingual cusp of Fieratherium undoubtedly represents a novelty for Metatheria. A simi- lar structure, with a homology traceable to the postproto- conal cingulum, has not been previously recognized for any South American taxon (including the well-known Itaboraı́ Figure 5. Superposition of upper (black line) and lower (grey line) teeth of Fieratherium sorex gen. et sp. nov. The distolingual cusp (hypocone) of the upper molar fits lingual to the talonid of the opposite lower tooth. D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 Late Oligocene shrew-like marsupial 559 or Las Flores fossil assemblages with basal stem marsupi- als; Paula Couto 1952; Marshall 1987; Goin et al. 1997; personal observations). Fieratherium is the only metathe- rian in which the postprotoconal cingulum is enlarged to form a cusp, such as the hypocone in some placental mammals. The presence of an enlarge distolingual cusp in mammals is associated with herbivory, because it allows the process- ing of vegetable matter. The radiation of mammals with this feature has been dated approximately synchronously in all continents by the Middle Eocene, and is perhaps correlated with the floral turnover associated with cooling and drying climatic trends (Hunter & Jernvall 1995). In Fieratherium, even if its distolingual cusp appears to be a post Eocene–Oligocene innovation, it cannot be related in functional terms with herbivory but with an insectiv- orous diet. The morphology of Fieraherium agrees with the taxonomic and ecological diversification that followed the global cooling event of the earliest Oligocene, recog- nized in Patagonia as the ‘Patagonian Hinge’ (Goin et al. 2010), based particularly on the analysis of the metathe- rian associations. This evolutionary event encompasses the major taxonomic and ecologic shift in the land-mammal faunas of southern South America at the Eocene–Oligocene boundary (Goin et al. 2010). The record of Fieratherium in the Oligocene (Deseadan SALMA) of Quebrada Fiera is consistent with this scenario. Tooth eruption sequence The generalized condition among marsupials and basal stem taxa, such as Alphadon, Pucadelphys and sparas- sodonts, is that the P3/p3 erupts and emerges at about the same time as the M4/m4 (Cifelli et al. 1996; Cifelli & Muizon 1998; van Nievelt & Smith 2005; Astúa & Leiner 2008; Forasiepi 2009). Among South American marsupi- als, the living Paucituberculata (i.e. Caenolestidae) is pecu- liar in this regard. The deciduous premolar is rudimentary and non-functional in occlusion and the P3/p3 significantly delays its eruption until long after the eruption of the last molar (i.e. the m4 has almost finished its eruption, whereas the p3 has not begun to erupt; Luckett & Hong 2000). With regard to fossil taxa, in Stilotherium there is proba- bly a delay in the eruption of the permanent premolar. As exemplified by specimen MACN-A 8464 of Stilotherium, the four lower molars are already erupted while the p3 did not completely finished the process (Luckett & Hong 2000, fig. 12). However, the molar cusps have almost no wear, suggesting that the delay in the eruption of p3 was possibly not as long as in caenolestids. In Fieratherium, the deciduous premolar is attached in the dentary and maxilla, while the M3 and m3 (according to the crypt) are partially erupted (Fig. 2B). If the accu- mulation of tissue below the DP3 represents the primordial P3 (see comments in the description above), then the erup- tion of P3 would be after the complete eruption of M3, and then probably about the same time as the last molar, if this tooth was present as in the crown group marsupials and close relatives. With regards to morphology, the DP3/dp3 of Fieratherium is proportionally smaller than the decidu- ous teeth of most didelphids (Online Supplementary Mate- rial Appendix 1), and it is reduced and vestigial in living paucituberculatans (Luckett & Hong 2000). No deciduous premolar has been reported in fossil paucituberculatans comparable to the morphology of Fieratherium. Because Fieratherium occupies a phylogenetic position basal to paucituberculatans (Fig. 4), it would be likely that the reduction in the size of the deciduous teeth of Fieratherium represents the plesiomorphic condition compared with the vestigial DP3/dp3 of caenolestids. Finally, it is worth mentioning that Fieratherium seems to have a peculiar molar eruption rate. In most living marsu- pials and basal stem taxa (e.g. Alphadon, Pucadelphys and sparassodonts), when the third molar has more than half of the crown erupted (as in the case of the specimen MCNAM- PV 3958 of Fieratherium), the first and the second molars are completely erupted with the crowns at the level of the alveolar line and the alveoli closed around the roots (e.g. Cifelli & Muizon 1998; Astúa & Leiner 2008; Forasiepi 2009). In Fieratherium, the molars seem to erupt at about the same time: by the time the third molar has more than half of the crown exposed, the first and second molars are below the alveolar line and the crypts are still opened (Fig. 3B). This pattern could be explained by a heterochronic shift in which either the posterior molars accelerate or the ante- rior molars retard the eruption with regard to the ancestor. Because Fieratherium is only known by an incomplete skull and dentary of a single specimen, it is not possible to support any of these possible causes. Morphological convergences with placental mammals Distinct features classify Fieratherium as a metatherian: one single deciduous tooth, a staggered second lower incisor (homologous with i3; Hershkovitz 1982), and a broad stylar shelf with tall stylar cusps (Kielan-Jaworowska et al. 2004). In addition, the presence of three premolars is consistent with Fieratherium being a metatherian. The dental morphology of Fieratherium argues in favour of an insectivoran diet. The cusps are pointed, the crests are sharp, and there are clear differences in height between trigon/trigonid and talon/talonid. The power stroke is verti- cal and steep, associated with a carnivorous diet (Butler 2001). In addition, the dentition of Fieratherium strongly resembles insectivorous placentals (i.e. eulipotyphlans) in several features suggesting strong convergences. The lower teeth have a large and procumbent first lower incisor (e.g. soricids such as Crocidura and Blarina, erinaceids such as Erinaceus, talpids, and fossil relatives such as Aptern- odus), the anterior premolars are reduced in size, with some D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 560 A.M. Forasiepi et al. single rooted elements (e.g. antemolars of erinaceids such as Erinaceus), and the hypoconulid is reduced or absent (e.g. erinaceids such as Erinaceus, and soricids such as Sorex) (Repenning 1967; Asher et al. 2002). The upper molars have an enlarged distolingual cusp in the posterior base of the protocone (hypocone), as in most eulipotyphlans and fossil relatives such as Micropternodus, Leptacodon, insectivoran afroriscidans (e.g. Russell 1960; Repenning 1967; McKenna 1968; Asher et al. 2002), and the para- conid is markedly smaller than the metaconid (e.g. as in some erinaceids such as Echinosorex and Erinaceus, some soricids as Crocidura and Blarina, and Nesophontes; Asher et al. 2002). In addition, the morphology of the DP3 of Fieratherium resembles the P4 of eulipotyphlans. There is one principal tall cusp (thought to be formed by paracone and metacone appresed to each other in Fieratherium and by the para- cone in eulipotyphlans), an acute parastyle (e.g. in some soricids such as Crocidura and Blarina, Nesophontes, and fossil relatives such as Micropternodus borealis, Aptern- odus gregori and A. major, the parastyle projects at a sharp angle from the anterior margin of the tooth; Russell 1960, Asher et al. 2002), and a low, lingually projected protocone. The dp3 shares at least with the p4 of some soricids (e.g. Sorex and Crocidura) the reduction of the paraconid and a relatively large protoconid (Repenning 1967). Placental ‘insectivorans’ were absent from South Ameri- can ecosystems during most of the Cenozoic. Despite some early work arguing in favour of ‘insectivorans’ (e.g. Amegh- ino 1894), their presence was later disproved. There are no eulipotyphlans currently in South America, with the excep- tion of the soricid shrew, Cryptotis, which is an element of the most recent migration into the continent reach- ing only the northern tip of the continent (Woodman & Péfaur 2007). The Paucituberculata were up to now the only clade with shrew-like morphological features. Fieratherium represents another lineage of shrew-like marsupials, with even stronger ‘insectivoran’ convergences in the dentition. Both groups would have occupied an ecological role similar to the eulipotyphlans during the Cenozoic in South Amer- ica, with the paucituberculatans more diverse and abundant. Fieratherium and the South American biogeographical context The Late Oligocene Deseadan faunal associations are repre- sented by several well-known and classical localities in Patagonia (e.g. Gran Barranca, Cabeza Blanca, Scarrit Pocket, La Flecha, Chubut and Santa Cruz provinces; Loomis 1914; Chafee 1952; Madden et al. 2010). Other Deseadan mammalian associations are known from the Bolivian localities of Salla and Lacayani (Hoffstetter et al. 1971; Vucetich 1989; Kay et al. 1998), the Fray Bentos Formation in Uruguay and Argentina (Mones & Ubilla 1978; Ubilla et al. 1994; Bond et al. 1998), the Moquegua Formation in Peru (Shockey et al. 2006), the Tremembé Formation in Brazil (Soria & Alvarenga 1989; Berqvist & Ribeiro 1998; Vucetich & Ribeiro 2003), and the Rı́o Maipo-Abanico Formation in Chile (Croft et al. 2008). Among them, the Patagonian and Bolivian associations are the best known and show significant differences. Quebrada Fiera is outside these localities and supports the idea of a mixed faunal association. It includes representatives from the southern and northern associations and exclu- sive species as a result of the intermediate latitudinal posi- tion of Mendoza in the palaeogeographical context of the South American Oligocene (Cerdeño 2011). Together with Mendozahippus (Notoungulata, Notohippidae; Cerdeño & Vera 2010), Fieratherium is also unique to the Quebrada Fiera association. Recent biogeographical reviews conducted by Morrone (2002, 2004a, 2004b, 2006; see also Goin et al. forthcom- ing) stressed the dual nature of South American biogeog- raphy. The southernmost tip of the continent (Patagonia and the Southern Andes) was regarded as belonging to a distinct region (the Andean Region) of the Austral Kingdom. In turn, the rest of South America was included within the Neotropical Region of the Holotropical King- dom. Much of our knowledge of mammalian evolution in South America, and especially of its Palaeogene history, comes from evidence from the Andean Region. The Paleocene-Eocene history of the intertropical regions of this continent is still largely unknown. The Quebrada Fiera locality in southern Mendoza Province lies near the boundary between the Andean and Neotropical regions. It is possible to assume that the origin and radiation of the Fieratherium lineage occurred north of Patagonia, and that its occurrence in Mendoza Province by Deseadan times corresponds to a relatively marginal area within the Neotropical realm. We suggest that continued prospecting in low latitude Palaeogene localities, such as those of Contamana (mid- to Late Eocene; Antoine et al. 2011) or Santa Rosa (?Late Eocene–?Early Oligocene; Goin & Candela 2004), in the Peruvian Amazonia, will offer better clues on the evolution of Fieratherium and the Paucituberculata clade. Conclusions A new metatherian, Fieratherium sorex gen. et sp. nov., is analysed and described. The specimen comes from the Quebrada Fiera locality, Mendoza Province, Argentina, from Late Oligocene deposits of Deseadan age. Fieratherium has a unique combination of features that clearly differentiates it from other metatherians hitherto recovered. The dentition of Fieratherium is highly conver- gent with ‘insectivorans’, including by the presence of a distolingual cusp (hypocone) derived from a poster- obasal cingulum, unrecorded in any marsupial or basal D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 Late Oligocene shrew-like marsupial 561 stem relative. The phylogenetic analysis suggests that Fieratherium is the sister-group of the Paucituberculata. Its occurrence in the Late Oligocene of Mendoza Province suggests that the lineage to which it belongs probably has its origin in more typical Neotropical regions. Acknowledgements We gratefully thank M. Reguero (MLP), A. Kramarz and D. Flores (MACN) for permitting access to the collections under their care; A.G. Martinelli for comments and the manual preparation of the fossil. R. Asher, N. Czaplewsky and R. Hutterer provided much useful advice in comparing the type specimen with several eutherian taxa; A. Manegold for the osteological specimens of insectivorans useful for comparisons; L. Berqvist for pictures of the Itaboarian taxa; S.D. Kay for English grammar revision, and the sugges- tions of two reviewers that helped to improve the origi- nal manuscript. We acknowledge use of the Willi Hennig Society edition of TNT. This work is a contribution to the projects PIP 0276 and PIP 1723 CONICET, and PICT 2010–1805 ANPCyT. Supplemental material Supplemental material is available online DOI: 10.1080/ 14772019.2013.799611 References Abello, M. A. 2007. Sistemática y bioestratigrafı́a de los Paucituberculata (Mammalia, Marsupialia) del Cenozoico de América del Sur. Unpublished PhD thesis, Universidad Nacional de La Plata, 381 pp. Abello, M. A. & Rubilar-Rogers, D. 2012. Revisión del género Abderites Ameghino, 1887 (Marsupialia, Paucituberculata). Ameghiniana, 49, 164–184. Ameghino, F. 1894. Enumération synoptique des espèces de mammifères fossiles des formations éocènes de Patagonie. Boletı́n de la Academia Nacional de Ciencias de Córdoba, 13, 259–452. Anders, U., Koenigswald, W., Ruf, I. & Smith S. H. 2011. Gener- alized individual dental age stages for fossil and extant placen- tal mammals. Paläontologische Zeitschrift, 85, 321–339. Anemone, R. L., Skinner, M. M. & Dirks W. 2012. Are there two distinct types of hypocone in Eocene primates? The ‘pseudo- hypocone’ of notharctines revisited. Palaeontologia Electron- ica, 15, 1–13. Antoine, P. O, Marivaux, L., Croft, D. A., Billet, G., Ganerød, M., Jaramillo, C., Thomas Martin, T., Orliac, M. J., Tejada, J., Altamirano, A. J., Duranthon, F., Fanjat, G., Rousse S. & Salas Gismondi, R. 2011. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society, Biological Sciences, 279, 1319–1326. Asher, R., McKenna, M. C., Emry, R. J., Tabrum, A. R. & Kron, D. G. 2002. Morphology and relationships of Aptern- odus and other extinct, zalambdodont, placental mammals. Bulletin of the American Museum of Natural History, 273, 1–117. Astúa, D. & Leiner, N. O. 2008. Tooth eruption sequence and replacement pattern in woolly opossums, genus Caluromys (Didelphimorphia: Didelphidae). Journal of Mammalogy, 89, 244–251. Beck, R. M. D., Godthelp H., Weisbecker, V., Archer, M. & Hand, S. J. 2008. Australia’s oldest marsupial fossils and their biogeographical implications. PLoS ONE 3(e1858), 8 pp. Berqvist, L. P. & Ribeiro, A. M. 1998. A paleomastofauna das bacias eoterciárias brasileiras e sua importância na datação das bacias de Iataboraı́ e Taubaté. Pp. 19–34 in S. Casadı́o (ed.) Paleógeno de América del Sur y de la Penı́nsula Antártica. Asociación Paleontológica Argentina, Buenos Aires, Publi- cación Especial 5. Bettini, F. 1982. Complejos efusivos terciarios presentes en las Hojas 30c y 32b (Puntilla del Huincán y Chos Malal), del sur de Mendoza y Norte del Neuquén, Argentina. 5◦ Congreso Latinoamericano de Geologı́a, Actas, 5, 79–114. Bond, M. & Pascual, R. 1983. Nuevos y elocuentes restos craneanos de Proborhyaena gigantea Ameghino, 1897 (Marsupialia, Borhyaenidae, Proborhyaeninae) de la Edad Deseadense. Un ejemplo de coevolución. Ameghiniana, 20, 47–60. Bond, M., Carlini, A. A., Goin, F. J., Legarreta, L., Ortiz- Jaureguizar, E., Pascual, R. & Uliana, M. A. 1995. Episodes in South American land mammal evolution and sedimenta- tion: testing their apparent concurrence in a Paleocene succes- sion from central Patagonia. 6◦ Congreso Argentino de Pale- ontologı́a y Bioestratigrafı́a, Actas, 47–58. Bond, M., López, G., Reguero, M. A., Scillato-Yané, G. J. & Vucetich, M. G. 1998. Los mamı́feros de la Formación Fray Bentos (Edad Deseadense, Oligoceno superior?) de las provincias de Corrientes y Entre Rı́os, Argentina. Pp. 41–50 in S. Casadı́o (ed.) Paleógeno de América del Sur y de la Penı́nsula Antártica. Asociación Paleontológica Argentina, Buenos Aires, Publicación Especial 5. Butler, P. M. 2001. Evolutionary transformations of the mammalian dentition. Mitteilung Museum für Naturkunde Berlin, Zoologische Reihe, 77, 167–174. Cerdeño, E. 2011. Quebrada Fiera (Mendoza), an important pale- obiogeographic center in the South American late Oligocene. Estudios Geológicos, 67, 375–384. Cerdeño, E. & Vera, B. 2007. Research on Cenozoic mammals in Mendoza Province, Argentina. Cuadernos del Museo Geominero, 8, 91–96. Cerdeño, E. & Vera, B. 2010. Mendozahippus fierensis gen. et sp. nov., new Notohippidae (Notoungulata) from the late Oligocene of Mendoza (Argentina). Journal of Vertebrate Paleontology, 30, 1805–1817. Cerdeño, E., Reguero, M. & Vera, B. 2010. Deseadan Archaeo- hyracidae (Notoungulata) from Quebrada Fiera (Mendoza, Argentina) in the paleobiogeographic context of the South American late Oligocene. Journal of Paleontology, 84, 1177–1187. Chafee, R. G. 1952. The Deseadan vertebrate fauna of the Scar- ritt Pocket, Patagonia. Bulletin of the American Museum of Natural History, 98, 507–562. Cifelli, R. L. & Muizon C. de 1998. Tooth eruption and replacement pattern in early marsupials. Comptes Rendus de l’Académie des Sciences, 326, 215–220. Cifelli, R. L., Rowe T. B., Luckett W. P., Banta J., Reyes R. & Howes R. I. 1996. Origin of marsupial pattern of tooth D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 562 A.M. Forasiepi et al. replacement: fossil evidence revealed by high resolution X- ray CT. Nature, 379, 715–718. Combina, A. M. & Nullo, F. 2002. Paleosuelos en la Formación Pircala-Coihueco en el área de Lomas de Coihueco, Mendoza: consecuencia del levantamiento paleógeno de la Cordillera Principal. 15◦ Congreso Geológico Argentino, Actas, 1, 760–764. Combina, A. M. & Nullo, F. 2008. El “diacronismo” de la Formación Agua de la Piedra (Terciario, Mendoza). 17◦ Congreso Geológico Argentino Actas, 1, 85–86. Cozzuol, M. 2006. The Acre vertebrate fauna: diversity, geogra- phy and time. Journal of South American Earth Sciences, 21, 185–203. Croft, D. A. 2007. The middle Miocene (Laventan) Quebrada Honda fauna, southern Bolivia and a description of its notoun- gulates. Palaeontology, 50, 277–303. Croft, D. A., Charrier, R., Flynn, J. J. & Wyss, A. R. 2008. Recent additions to knowledge of Tertiary mammals from the Chilean Andes. 1◦ Simposio de Paleontologı́a en Chile, Santiago de Chile, Resumenes 1–7. Forasiepi A. M. 2009. Osteology of Arctodictis sinclairi (Mammalia, Metatheria, Sparassodonta) and phylogeny of Cenozoic metatherian carnivores from South America. Mono- grafı́as del Museo Argentino de Ciencias Naturales n.s., 6, 1–174. Gelfo, J. N., Goin F. J., Woodburne, M. O. & Muizon C. de 2009. Biochronological relationships of the earliest South American Paleogene mammalian faunas Palaeontology, 52, 251–269. Goin, F. J. & Candela, A. M. 2004. New Paleogene marsupi- als from the Amazon Basin of Eastern Peru. Science Series, Natural History Museum of Los Angeles County, 40, 15–60. Goin, F. J., Candela A. M. & Forasiepi A. M. 1997. New middle Paleocene marsupials from central Patagonia. Jour- nal of Vertebrate Paleontology, 17, 49A. Goin, F. J., Case, J. A., Woodburne, M. O., Vizcaı́no, S. F. & Reguero, M. A. 1999. New discoveries of “opossum-like” marsupials from Antarctica (Seymour Island, medial Eocene). Journal of Mammalian Evolution, 6, 335–365. Goin, F. J., Sánchez-Villagra, M. R., Abello, A. & Kay, R. F. 2007. A new generalized paucituberculatan marsupial from the Oligocene of Bolivia and the origin of ‘shrew-like’ opos- sums. Palaeontology, 50, 1267–1276. Goin, F. J., Candela, A. M., Abello, M. A. & Oliveira, E. V. 2009. Earliest South American paucituberculatans and their signifi- cance in the understanding of ‘pseudodiprotodont’ marsupial radiations. Zoological Journal of the Linnean Society, 155, 867–884. Goin, F. J., Abello, M. A. & Chornogubsky, L. 2010. Middle Tertiary marsupials from central Patagonia (early Oligocene of Gran Barranca): understanding South America’s Grande Coupure. Pp. 69–105 in R. H. Madden, A. A. Carlini, M. G. Vucetich & R. F. Kay (eds) The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia. Cambridge University Press, Cambridge. Goin, F. J., Zimicz, A. N., Forasiepi, A. M., Chornogub- sky, L. C. & Abello, M. A. Forthcoming. The rise and fall of South American metatherians: contexts, adaptations, radiations, and extinctions. In A. L. Rosenberger & M. F. Tejedor (eds) Origins and Evolution of Cenozoic South Amer- ican Mammals. Springer Verlag, New York. Goloboff, P. A., Farris, J. S. & Nixon, K. C. 2008. T.N.T., a free program for phylogenetic analysis. Cladistics, 24, 774–786. Gorroño, R., Pascual, R. & Pombo, R. 1979. Hallazgo de mamı́feros eógenos en el sur de Mendoza. Su implicancia en las dataciones de los “rodados lustrosos” y del primer episodio orogénico del Terciario en esa región. 7◦ Congreso Geológico Argentino Actas, 475–487. Gregory, W. K. 1934. A half century of trituberculy, the Cope- Osborn theory of dental evolution. Proceedings of the Amer- ican Philosophical Society, 73, 169–317. Groeber, P. 1946. Observaciones geológicas a lo largo del meridiano 70◦. 1, Hoja Chos Malal. Revista de la Sociedad Geológica Argentina, 1, 177–208. Hershkovitz, P. 1982. The staggered marsupial lower third incisor (i3). Geobios, Mémoire Spécial, 6, 191–200. Hershkovitz, P. 1995. The staggered marsupial third lower incisor: hallmark of Cohort Didelphimorphia, and description of a new genus and species with staggered i3 from the Albian (Lower Cretaceous) of Texas. Bonner Zoologische Beiträge, 45, 153–169. Hoffstetter, R., Martı́nez, C., Mattauer, M. & Tomasi, P. 1971. Lacayani, un nouveau gisement bolivien de Mammifères déséadiens (Oligocène inférieur). Comptes Rendus de l’Académie des Sciences, 273, 2215–2218. Hunter J. P. & Jernvall J. 1995. The hypocone as a key inno- vation in mammalian evolution. Proceedings of the National Academy of Sciences USA, 92, 10718–10722. Huxley, J. S. 1880. On the application of the law of evolution to the arrangement of the Vertebrata, and more particular to the Mammalia. Proceedings of the Zoological Society of London, 43, 649–662. Johanson, Z. 1996. Revision of the Late Cretaceous North Amer- ican marsupial genus Alphadon. Palaeontographica, 242, 127–184. Kay, R. F., Madden, R. H., Cifelli, R. L. & Flynn, J. J. 1997. Vertebrate paleontology in the Neotropics. The Miocene fauna of La Venta, Colombia. Smithsonian Institution Press, Wash- ington & London, 592 pp. Kay, R. F., MacFadden, B. J., Madden, R. H., Sandeman, H. & Anaya, F. 1998. Revised age of the Salla Beds, Bolivia, and its bearing on the age of the Deseadan South American land mammal “Age”. Journal of Vertebrate Paleontology, 18, 189–199. Kielan-Jaworowska, Z., Cifelli, R. L. & Luo, Z. X. 2004. Mammals from the age of dinosaurs. Origin, evolution, and structure. Columbia University Press, New York, 630 pp. Ladevèze, S. & Muizon, C. 2010. Evidence of early evolu- tion of Australidelphia (Metatheria, Mammalia) in South America: phylogenetic relationships of the metatherians from the Late Paleocene of Itaboraı́ (Brazil) based on teeth and petrosal bones. Zoological Journal of the Linnean Society, 159, 746–784. Latrubesse, E. M., Cozzuol, M., da Silva-Caminha, S. A. F., Rigsby, C. A., Absy, M. L. & Jaramillo, C. 2010. The Late Miocene paleogeography of the Amazon Basin and the evolu- tion of the Amazon River system. Earth-Science Reviews, 99, 99–124. Linnaeus, C. 1758. Systema naturae per regna tria naturae, secundum classis, ordines, genera, species cum characteribus, differentiis, synonyms loci. 10th revised edition, Volume 1. Laurentii Salvii, Stockholm. Loomis, F. B. 1914. The Deseado Formation of Patagonia. Amherst College, New Haven, 232 pp. Luckett P. W. & Hong N. 2000. Ontongenetic evidence for dental homologies and premolar replacement in fossil and extant caenolestids (Marsupialia). Journal of Mammalian Evolution, 7, 109–127. Madden, R. H., Carlini, A. A., Vucetich, M. G. & Kay, R. F. 2010. The paleontology of Gran Barranca. Evolution and D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 Late Oligocene shrew-like marsupial 563 environmental change through the middle Cenozoic of Patag- onia. Cambridge University Press, Cambridge, 448 pp. Marshall, L. G. 1980. Systematics of the South American marsu- pial family Caenolestidae. Fieldiana Geology, New Series, 5, 1–145. Marshall, L. G. 1987. Systematics of Itaboraian (Middle Pale- ocene) age “opposum-like” marsupials from the limestone quarry at São José de Itaboraı́, Brazil. Pp. 91–160 in M. Archer (ed.) Possums and opossums: studies in evolution. Surrey Beatty & Sons and the Royal Zoological Society of New South Wales, Sydney. McKenna, M. C. 1968. Leptacodon, an American Paleocene Nyctithere (Mammalia, Insectivora). American Museum Novitates, 2317, 1–12. Mones, A. & Ubilla, M. 1978. La edad Deseadense (Oligo- ceno inf.) de la Formación Fray Bentos y sucontenido paleontológico con especial referencia a la presencia de Proborhyaena cf. gigantea Ameghino (Marsupialia: Borhyaenidae) en el Uruguay. Nota preliminar. Comunica- ciones Paleontológicas del Museo de Historia Natural de Montevideo, 1, 151–158. Morrone, J. J. 2002. Biogeographical regions under track and cladistic scrutiny. Journal of Biogeography, 29, 149–152. Morrone, J. J. 2004a. Panbiogeografı́a, componentes bióticos y zonas de transición. Revista Brasileira de Entomologia, 48, 149–162. Morrone, J. J. 2004b. La Zona de Transición sudamericana: caracterización y relevancia evolutiva. Revista Entomológica Chilena, 28, 41–50. Morrone, J. J. 2006. Biogeographic areas and transition zones of Latin America and the Caribbean islands based on panbio- geographic and cladistic analyses of the entomofauna. Annual Review of Entomology, 51, 467–94. Narciso, V., Santamarı́a, G. & Zanettini, J. C. M. 2004. Hoja geológica 3769-I “Barrancas” Provincias de Mendoza y Neuquén. Instituto de Geologı́a y Recursos Minerales, Boletı́n del Servicio geológico y Minero Argentino, 253, 1–60. Osborn H. F. 1888. The nomenclature of the mammalian molar cusps. The American Naturalist, 22, 926–928. Osborn H. F. 1897. Trituberculy: a review dedicated to the late Professor Cope. The American Naturalist, 31, 993–1016. Osborn, H. F. 1907. Evolution of mammalian molar teeth to and from the triangular type. Macmillan Company, New York, 250 pp. Pascual, R. & Odreman Rivas, O. 1973. Las unidades estratigráficas del Terciario portadoras de mamı́feros. Su distribución y sus relaciones con los acontecimientos diastróficos. 5◦ Congreso Geológico Argentino, Actas, 3, 293–338. Pascual, R., Ortega, E. J., Gondar D. & Tonni, E. P. 1965. Las edades del Cenozoico mamalı́fero de la Argentina, con espe- cial atención a aquéllos del territorio bonaerense. Anales de la Comisión de Investigaciones Cientı́ficas de Buenos Aires, 6, 165–193. Paula Couto, C. de. 1952. Fossil mammals from the beginning of the Cenozoic of Brazil. Marsupialia: Didelphidae. American Museum Novitates, 1559, 1–27. Prámparo, M. B., González Riga, B. J., Cerdeño, E., Calvo, J. O., Reguero, M. & Previtera, E. 2006. Enfoque multidis- ciplinario para el estudio de nuevos hallazgos paleontológicos en el Cretácico y Paleógeno del sur de Mendoza. 9◦ Congreso Argentino de Paleontologı́a y Bioestratigrafı́a, Resúmenes, 263. Repenning, C. A. 1967. Subfamilies and genera of the Soricidae. Geological Survey Professional Paper, 565, 1–74. Russell, D. A. 1960. A review of the Oligocene insecti- vore Micropternodus borealis. Journal of Paleontology, 34, 940–949. Sánchez Villagra, M. R. & Kay, R. F. 1996. Do phalangeriforms (Marsupialia: Diprotodontia) have a “hypocone”? Australian Journal of Zoology, 44, 461–467. Sánchez Villagra, M. R., Aguilera, O. A. & Carlini, A. A. 2010. Urumaco and Venezuelan paleontology. The fossil record of the Northern neotropics. Indiana University Press, Blooming- ton & Indianapolis, 289 pp. Sánchez Villagra, M., Ladevèze, S., Horovitz, I., Argot, C. Hooker, J. J., Macrini, T. E., Martin, T., Moore-Fay, S. Muizon, C. de, Schmelzle, T. & Asher, R. J. 2007. Excep- tionally preserved North American Paleogene metatherians: adaptations and discovery of a major gap in the opossum fossil record. Biology Letters, 3, 318–322. Shockey B. J., Salas, R., Quispe, R., Flores, A., Sargis, E. J., Acosta, J., Pino, A., Jarica, N. J. & Urbina, M. 2006. Discovery of deseadan fossils in the upper Moquegua Forma- tion (late Oligocene–?early Miocene) of Southern Peru. Jour- nal of Vertebrate Paleontology, 26, 205–208. Simpson, G. G. 1936. Studies of the earliest mammalian denti- tions. Dental Cosmos (August–September), 1–24. Simpson, G. G. 1970. Mammals from the early Cenozoic of Chubut, Argentina. Breviora, 360, 1–13. Simpson, G. G. 1980. Splendid isolation. The curious history of South American mammals. Yale University Press, New Haven, 266 pp. Soria, M. F. & Alvarenga, H. M. F. 1989. Nuevos restos de mamı́feros de la cuenca de Taubaté, Estado de Sao Paulo, Brasil. Anais de la Academia Brasileira de Ciências, 61, 157–175. Tedford, R. H. & Woodburne, M. O. 1987. The Ilariidae, a new family of vombatiform marsupials from Miocene strata of South Australia and an evaluation of the homology of molar cusps in the Diprotodontia. Pp. 401–418 in M. Archer (ed.) Possums and opossums: studies in evolution. Surrey Beatty & Sons and the Royal Zoological Society of New South Wales, Sydney. Tedford, R. H. & Woodburne, M. O. 1998. The diprotodon- tian ‘hypocone’ revisited. Australian Journal of Zoology, 46, 249–250. Ubilla M., Perea D. & Bond, M. 1994. The Deseadan Land Mammal Age in Uruguay and the report of Scarrittia robusta nov. sp. (Leontiniidae, Notoungulata) in the Fray Bentos Formation (Oligocene–?Lower Miocene). Geobios, 27, 95–102. van Nievelt A. F. H. & Smith K. K. 2005. Tooth eruption in Monodelphis domestica and its significance for phylogeny and natural history. Journal of Mammalogy, 86, 333–341. Van Valen, L. M. 1994. Serial homology: the crests and cusps of mammalian teeth. Acta Palaeontologica Polonica, 38, 145–158. Vera, B. & Cerdeño, E. 2009. Presencia de Notohippidae en el Deseadense (Oligoceno tardı́o) de Quebrada Fiera (Mendoza, Argentina). 24◦ Jornadas Argentinas de Paleontologı́a de Vertebrados, Resúmenes, 62. Vizcaı́no, S. F., Kay, R. F. & Bargo, M. S. 2012. Early Miocene paleobiology in Patagonia. High-latitude paleocommunities of the Santa Cruz Formation. Cambridge University Press, Cambridge, 378 pp. Voss, R. S. & Jansa, S. A. 2003. Phylogenetic studies on didelphid marsupials II. Nonmolecular data and new IRBP sequences: separate and combined analyses of didelphine relationships with denser taxon sampling. Bulletin of the American Museum of Natural History, 276, 1–82. D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5 564 A.M. Forasiepi et al. Vucetich, M. G. 1989. Rodents (Mammalia) of the Lacayani fauna revisited (Deseadan, Bolivia). Comparison with new Chinchillidae and Cephalomyidae from Argentina. Bulletin du Museum national d’Histoire naturelle, 11, 233–247. Vucetich, M. G. & Ribeiro, A. M. 2003. A new and primi- tive rodent from the Tremembé Formation (late Oligocene) of Brazil, with comments on the morphology of the lower premolars of caviomorph rodents. Revista Brasileira de Pale- ontologia, 5, 73–82. Woodburne, M. O., Tedford, R. H., Archer, M. & Pledge, N. S. 1987a. Madakoala, a new genus and species of Miocene koalas (Marsupialia; Phascolarctidae) from South Australia, and a new species of Perikoala. Pp. 293–317 in M. Archer (ed.) Possums and opos- sums: studies in evolution. Surrey Beatty & Sons and the Royal Zoological Society of New South Wales, Sydney. Woodburne, M. O., Tedford, R. H. & Archer, M. 1987b. New Miocene ringtail possums (Marsupialia: Pseudocheiri- dae) from South Australia. Pp. 639–679 in M. Archer (ed.) Possums and opossums: studies in evolution. Surrey Beatty & Sons and the Royal Zoological Society of New South Wales, Sydney. Woodman, N. & Péfaur, J. 2007. Order Soricomorpha Gregory, 1910. Pp. 177–187 in A. L. Gardner (ed.). Mammals of South America, Volume 1 M marsupials, xenarthrans, shrews, and bats. University of Chicago Press, Chicago. D ow nl oa de d by [ A m er ic an M us eu m o f N at ur al H is to ry ] at 0 7: 56 1 0 M ar ch 2 01 5