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Journal of Mammalian Evolution

, Volume 24, Issue 1, pp 39–55 | Cite as

A New South American Paleogene Land Mammal Fauna, Guabirotuba Formation (Southern Brazil)

  • Fernando A. SedorEmail author
  • Édison V. Oliveira
  • David D. Silva
  • Luiz A. Fernandes
  • Renata F. Cunha
  • Ana M. Ribeiro
  • Eliseu V. Dias
Original Paper

Abstract

The Paleogene vertebrate-bearing sites of Brazil are restricted to few formations such as Maria Farinha (Late Cretaceous-early Paleocene), Itaboraí (early Eocene), Entre-Córregos (Eocene-Oligocene), and Tremembé (late Oligocene-early Miocene). A new Paleogene fauna is reported from an outcrop of the Guabirotuba Formation located at Curitiba, Paraná State, southern Brazil. The Guabirotuba Formation is a stratigraphic unit of the Curitiba Basin, which belongs to the Cenozoic continental rift system of southeastern Brazil, a predominantly half-graben and horst system. The sedimentary facies indicate a fluvial distributary depositional system associated with floodplain, generated under humid climate conditions alternating with drier periods. This new Paleogene fauna, here named the Guabirotuba Fauna, has invertebrate and vertebrate taxa, including mammals (Cingulata, Notoungulata, Astrapotheria, and Metatheria). The fossil remains of seven armored xenarthrans are identified, including the description of a new species and genus named Proeocoleophorus carlinii. The Guabirotuba ungulates are assigned to Interatheriidae, Oldfieldthomasiidae, and Astrapotheria. The metatherian mammals are represented by a sparassodont, a palaeothentoid, and an argyrolagoid. This new mammalian fauna preliminarily suggests a late middle Eocene age (Barrancan South American Land Mammal Age) for the Guabirotuba Formation.

Keywords

Xenarthra Notoungulata Astrapotheria Metatheria Curitiba Basin Guabirotuba Fauna 

Introduction

During most of the Cenozoic Era, the South American continent remained isolated allowing the evolution of a peculiar and endemic mammalian fauna. In recent years, there has been an increment in knowledge on the systematics, biogeography, biostratigraphy, and geochronology of Paleogene mammals as a result of: new localities found, such as Santa Rosa (Campbell 2004), Tinguiririca (Flynn et al. 2003), Contamana (Antoine et al. 2016a, 2016b); the review of previously known localities, like Gran Barranca, Las Flores (Woodburne et al. 2014a); and new findings, as for example those in the Geste Formation (García-López and Babot 2015) and Itaboraí (Oliveira and Goin 2011).

The understanding of geochronology, taxonomy, and succession of South American mammal faunas is the basis for recognition of nearly 20 intracontinental biochronological units of the South American Land Mammal Ages (SALMAs) (e.g., Simpson 1940, 1948, 1967, 1980; Patterson and Pascual 1968; Marshall et al. 1983; MacFadden 1985; Marshall 1985; Pascual and Ortiz-Jaureguizar 1990; Flynn and Swisher 1995; Pascual et al. 1996; Kay et al. 1999; Gelfo et al. 2009; Woodburne et al. 2014b). Nevertheless, there are considerable temporal and geographic gaps in the paleontological records and, with the exception of a few localities (e.g., Tinguiririca, Tiupampa, and Itaboraí), almost all knowledge about Paleogene SALMAs are defined from records in high-latitude regions of the South American continent, especially in Argentinean Patagonia.

Until now, Brazilian Paleogene fossil-bearing sites are restricted to few formations such as Maria Farinha (Late Cretaceous-early Paleocene), Itaboraí (early Eocene), Entre-Córregos (Eocene-Oligocene), and Tremembé (late Oligocene-early Miocene). Fossil mammals are only recorded in the Itaboraí and Taubaté basins. Nowadays, the Itaboraí Basin is totally flooded, making new geological and paleontological studies difficult, except those based on fossil collections. On the other hand, most of the Taubaté Basin fossil records come from Fazenda Santa Fé, a locality with a continued exploitation of clay minerals.

The fossil vertebrates findings in the Guabirotuba Formation (Curitiba Basin) in Paraná State, southern Brazil, started with Liccardo and Weinschütz (2010) who presented a ziphodont tooth assigned to a mesosuchian crocodylomorph (Sebecidae) and Rogério et al. (2012) with the record of turtle remains assigned to Pleurodira. Recently, Sedor et al. (2014) reported a new Paleogene fauna for the Guabirotuba Formation including several mammalian taxa distributed within Notoungulata, Metatheria, and Xenarthra, and also Osteichthyes, Amphibia (Anura), Testudines (Pleurodira), Crocodylia (Sebecosuchia), Aves (Phorusrhacidae), Gastropoda, and invertebrate ichnofossils. The new fauna is here named the Guabirotuba Fauna and its biochronological implications are considered. The present contribution preliminarily details the discovery of this new locality including the description of a new form of cingulate and the occurrence of taxa already known for other South American localities. The fossils presented here are restricted to mammal taxa leaving others to future contributions.

Geological Setting

The Curitiba Basin is in the southernmost portion of the Cenozoic continental rift system of southeastern Brazil (Almeida 1976; Riccomini et al. 2004), which is aligned with rift valleys with 1200 km in extension along the coastal Atlantic mountain ridge known as “Serra do Mar.” This rift system has formed taphrogenic sedimentary basins filled during the Cenozoic such as Curitiba, São Paulo, Taubaté, Resende, Volta Redonda, and Itaboraí basins (Melo et al. 1985). The Curitiba Basin covers 3000 km2 with maximum preserved thickness of around 80 m of sediments (Fig. 1a) and the Guabirotuba Formation is the main stratigraphic unit of the basin (Salamuni et al. 2003).
Fig. 1

Location map of the Guabirotuba Fauna outcrop, Curitiba, Paraná State, southern Brazil. a Guabirotuba Formation area and fossiliferous site; b outcrop stratigraphic column. 1) massive greenish gray mud; 2) immature yellowish gray sand with poorly defined cross-bedding stratification, sometimes conglomeratic in its base with fining-up strata to the top and locally with laminar calcretes

The Guabirotuba Formation is a unit constituted by deposits of a fluvial distributary system composed generally of immature subarkozic sands and muds, with gravel deposits as intercalations restrict to the basin borders (Bigarella and Salamuni 1962; Lima et al. 2013). The fluvial successions are of metric thickness, with erosive bases. They are formed by immature yellowish to greenish gray gravel sand fining upward, where they end as a greenish gray mud (Fig. 1b). These corresponds to deposits of distal areas of alluvial fans dominated by deposits of shallow braided channels and intercalated floodplain deposits of distributary fluvial system (sensu Nichols and Fisher 2007). Calcrete horizons attributed to development of immature paleosols occur at the top of the section (Lima et al. 2013).

The absence of typical aeolian deposits or sedimentary exposition features in the Guabirotuba Formation, and the abundance of mud, indicates the predominance of humid climatic conditions with alternation of drier periods as indicated by calcrete horizons present in the unit (Cunha 2011; Lima et al. 2013). The presence of the mostly aquatic Pleurodira fossil turtles is also an indication of more humid conditions (Rogério et al. 2012) than previously proposed (Bigarella and Salamuni 1962; Becker 1982; Salamuni et al. 1999; Liccardo and Weinschütz 2010). The depositional context consisted of an area of smooth topography, where sandy laminar flows spread out over a muddy floodplain, formed mainly of older muddy flows. The vegetation could develop in this environment forming pedogenetic horizons also influenced by humidity from groundwater source (Lima et al. 2013).

The age of Guabirotuba Formation remains controversial due to the lack of accurate chronological data. Bigarella et al. (1961) and Bigarella and Salamuni (1962) proposed a Plio-Pleistocene age to the unit. Becker (1982) assigned a Pliocene age to the formation, while Salamuni (1998) suggested that the deposition occurred between the early Oligocene to mid-Miocene. Coimbra et al. (1995) postulated an age at the late Eocene-early Oligocene limit, and Salamuni et al. (2003) proposed the deposition from Oligocene to the early Miocene. Garcia et al. (2013) proposed a Pliocene age based on palynomorphs. Sedor et al. (2014) proposed, preliminarily, an older age from middle Eocene to early Oligocene, which is revisited in this contribution.

Material and Methods

All fossils came from the same location, an outcrop of the Guabirotuba Formation (Curitiba Basin) near the border of the Curitiba and Araucária municipalities in Paraná State, south of Brazil, 25°30′30″S, 49°20′30″W (Fig. 1a). This outcrop was previously described by Liccardo and Weinschütz (2010) and Rogério et al. (2012).

The research in this outcrop began a few years ago and most of the fossils were collected by traditional paleontological methods. Nevertheless, samples of the sediment has been sieved and picked under stereomicroscope, and fossils of millimetric size were found and will be treated in forthcoming works. The fossils are housed in the Museu de Ciências Naturais, Setor de Ciências Biológicas, Universidade Federal do Paraná (MCN-SCB-UFPR).

The μCT-Scanning was used to analyze ungulate and metatherian specimens. The anatomical nomenclature follows: cingulate osteoderms - based on Ciancio et al. (2013), Notopithecinae - Vera (2016), Oldfieldthomasiidae - García-López and Babot (2015), Astrapotheria - Kramarz and Bond (2009), and metatherians - Goin et al. (2010).

Taxonomy

Most of the studied specimens are describe preliminarily as they require comparisons and more accurate analysis. However, a new species of cingulate is described. Specimens referred to Notoungulata and Astrapotheria are subject of the doctoral thesis of one of the authors (D.D.S.) in which they will be described and figured in details.

Superorder XENARTHRA Cope, 1889

Order CINGULATA Illiger, 1811

Family incertae sedis

Proeocoleophorus, gen. nov.

Type species: Proeocoleophorus carlinii, sp. nov.

Etymology: From Pro (before in Latin) and Eocoleophorus, generic name of a cingulate from the Oligocene of the Tremembé Formation (Taubaté Basin, Brazil).

Diagnosis: As for the type and single species.

Proeocoleophorus carlinii, sp. nov.

(Fig. 2a-i)
Fig. 2

Selected specimens of Proeocoleophorus carlinii, gen. et sp. nov., from Guabirotuba Formation, late middle Eocene, Paraná State, southern Brazil; a MCN.P.1200, movable osteoderm; b MCN.P.1205, movable osteoderm; c MCN.P.1212, complete buckler osteoderm; d MCN.P.1213, complete buckler osteoderm; e MCN.P.1217, complete buckler osteoderm; f MCN.P.1208, complete buckler osteoderm; g MCN.P.1210, complete buckler osteoderm; h MCN.P.1211, incomplete buckler osteoderm, and i MCN.P.1215, complete buckler osteoderm. Scale bar =1 cm

Holotype: MCN.P.1200, a movable osteoderm.

Hypodigm: The holotype and MCN.P.1201, 1202, 1203, 1204, incomplete movable osteoderms; MCN.P.1205, 1206, 1207 complete movable osteoderms; MCN.P.1208, 1209, 1210, 1211, 1212, 1213, 1214, 1215, 1216, 1217, 1218, 1219, 1222 complete buckler osteoderms; MCNP. 1220, 1221, incomplete buckler osteoderms; MCN.P. 1223, 1224 incomplete cephalic osteoderms.

Etymology: carlinii, in honor of paleontologist Alfredo Armando Carlini, from Museo de La Plata, Argentina, expert in fossil xenarthrans.

Diagnosis: Osteoderms with a smooth external surface. Movable osteoderms with only two anterolateral figures, main figure narrow anteriorly and wide posteriorly with a small number of foramina (one to three) in the sulci of the main figure. The central keel is absent in the main figure of buckler and movable osteoderms. Large buckler osteoderms with a hexagonal to ovoid main figure and with two or three external surface foramina at the anterior area of the main sulcus. Buckler osteoderms without foramina in the anterior margin of the anterior figures. The marginal area of the main figure in buckler osteoderms is narrow and depressed.

Horizon and locality: Guabirotuba Formation (Curitiba Basin), an outcrop located in the city of Curitiba in Paraná State, Brazil (Fig. 1a), coordinates 25°30′30″S, 49°20′30″W.

Temporal distribution: Late middle Eocene (Barrancan SALMA).

Description: The holotype is a complete movable osteoderm with 30.0 mm long, 15.0 mm wide, and 6.0 mm thick (Fig. 2a). The anterior articular surface is short relative to the ornamented area, and presents an irregular and rugose surface, which is also observed in the transition. The anterolateral figures are right triangular shaped, slightly asymmetrical, and convex. The sulcus that delimits the main figure is very shallow and bears only one or two larger posterior foramina. The main figure is convex, narrow anteriorly, and wide posteriorly. The central keel is absent. The piliferous system on the posterior border is absent. The inner side of the movable osteoderms is concave. The buckler osteoderms are large and thick. The articular borders are strongly serrate. The anterior and anterolateral figures are convex and generally four to five, being one of them smaller and do not contact the main figure. The outline of the main figure is roughly ovoid or nearly hexagonal and some osteoderms have small and shallow depressions. The sulcus that delimits the main figure bears only two large foramina. Two incomplete, irregular osteoderms (MCN.P.1210, 1211; Fig. 2g-h) are approximately sub-rectangular in shape, bearing a large main figure and small peripheral figures ranging from two to four. Specimen MCN.P.1208 is a typical buckler osteoderm (Fig. 2f) that is 31.8 mm long, 22.6 mm wide, and 8.4 mm thick.

Remarks: Compared to other taxa described for the Paleogene, P. carlinii seems to be more related to Eocoleophorus glyptodontoides Oliveira et al., 1997, from the late Oligocene of Brazil, which also occurs in late Oligocene of Bolivia (Carlini and Scillato-Yané 1999) and late-middle Eocene of Peru (Antoine et al. 2016a), and shares similarities with Yuruatherium intortum (Ameghino, 1902) from the late Eocene (Mustersan SALMA) of Argentina, and Yuruatherium tropicalis Ciancio et al., 2013, from Peruvian? late Eocene-early Oligocene. The P. carlinii of Guabirotuba Fauna differs from E. glyptodontoides in having features such as (i) fewer anterior and anterolateral figures without anterior foramina at buckler osterderms, (ii) much smaller number of external foramina in buckler and movable osteoderms, (iii) an ovoid to near hexagonal main figure in buckler osteoderms, and (iv) absence of keel at the main figure. Furthermore, in some osteoderms of Proeocoleophorus the main figure is delimited by straight sulci forming a hexagonal-like figure, which is different in E. glyptodontoides (Oliveira et al. 1997). The presence in Proeocoleophorus of a smooth external surface of the osteoderms, a smaller number of external foramina, and a very well delimited main figure differentiates this new genus from Yuruatherium. Proecoleophorus carlinii presents similarities with the osteoderm from Contamana assigned to E. glyptodontoides (CTA-29 locality; Antoine et al. 2016a) but differs from it in having foramina.

Family incertae sedis

Machlydotherium Ameghino, 1902

Machlydotherium sp.

(Fig. 3a-b)
Fig. 3

Cingulates from Guabirotuba Formation. a MCN.P.1232, buckler osteoderm of Machlydotherium sp.; b MCN.P.1234, incomplete movable osteoderms of Machlydotherium sp.; c MCN.P.1225, buckler osteoderm of Astegotheriini, gen. et sp. indet.; d MCN.P.1228, incomplete movable osteoderm of Astegotheriini, gen. et sp. indet.; e MCN.P.1231(2), movable osteoderm of Utaetus sp.; f MCN.P.1246, buckler osteoderm of Meteutatus sp.; g MCN.P.1243, buckler osteoderm of Parutaetus, sp. indet.; h MCN.P.1240, buckler osteoderm of Parutaetus, sp. indet.; i MCN.P.1250, incomplete movable osteoderm of Parutaetus, j MCN.P.1242, buckler osteoderm of Parutaetus, sp. indet.; k MCN.P.1248, buckler osteoderm of Euphractini, indet.; l MCN.P.1247, incomplete movable osteoderm of Euphractini, indet.; Scale bar =5 mm

Type species: Machlydotherium asperum Ameghino, 1902

Referred material: MCN.P.1232, complete buckler osteoderm (Fig. 3a); MCN.P.1233, incomplete movable osteoderm (Fig. 3b); MCN.P.1234, 1235, 1236, 1237, 1238, 1239, six incomplete movable osteoderms.

Temporal distribution: Late middle Eocene to early Oligocene, Barrancan to Tinguirirican (Ciancio et al. 2013).

Description: Large osteoderms, with a typical buckler osteoderm (Fig. 3a) measuring 20.0 mm long, 17.2 mm wide, and 7.3 mm thick; a movable osteoderm (Fig. 3b) is more than 31.0 mm long, 16.6 mm wide, and 6.2 mm thick (in the posterior area). The buckler osteoderm is sub-quadrangular in shape, externally concave, and almost flat medially. The external surface is highly punctuated, which results in a rugose aspect, with an oblique central keel. The transition zones of the movable osteoderms are poorly distinct, relatively short, and also rugose. Although incomplete, MCN.P.1235 and MCN.P.1238 present two to three large anterior foramina on the external surfaces. Three foramina of the piliferous system are present in the posterior border of at least one movable osteoderm. The articular surfaces are slightly undulated without clear serrations.

Remarks: The highly punctuated surface (rugose), the presence of two or three large anterior foramina, and the marginal areas with poor serrations suggest that these osteoderms from Guabirotuba Formation could be belong to Machlydotherium Ameghino, 1902, from Argentina (Ciancio et al. 2013). Machlydotherium asperum Ameghino, 1902, was redescribed by Simpson (1948) from the Mustersan of the Patagonia, Argentina. However, the materials described herein differ from M. asperum in being smaller, in showing a longer anterior articular surface in movable osteoderms, as well as the presence of an oblique central keel in buckler osteoderms. Compared to Machlydotherium ater Ameghino, 1902, the buckler osteoderm described herein does not exhibit central foramina, the external surface is less rugose, and the movable osteoderms presents a smaller articular area. The other two species described by Ameghino (1902) include a poor defined taxon ?M. sparsum, which according to Simpson (1948) is not distinguished from M. asperum, and ?M. intortum, which belongs to Yuruatherium according to Ciancio et al. (2013).

Family Dasypodidae Gray, 1821

Subfamily Dasypodinae Gray, 1821

Tribe Astegotheriini Ameghino, 1906

Gen. et sp. indet.

(Fig. 3c-d)

Temporal distribution: The Astegotheriini are from early Eocene to middle Miocene, Itaboraian-Laventan (Oliveira and Bergqvist 1998; Ciancio et al. 2013).

Referred material: MCN.P.1225, complete and MCN.P.1226 incomplete buckler osteoderms. MCN.P.1227, an incomplete semimovable osteoderm; MCN.P.1228, 1229, 1230, incomplete movable osteoderms.

Description: The buckler osteoderms are sub-quadrangular and their external surfaces are smooth; on the anterior area, four to six large foramina are placed as an arch surrounding the neck of the main figure; these foramina decrease in size posteriorly. The main figure is lageniform, bears a longitudinal keel, and two foramina on each side asymmetrically placed. Presents two poorly defined asymmetrical anterior figures and a pair of small anterolateral ones. An isolated foramen is located on the surface near the very shallow sulcus delimiting the anterior figures. Six foramina are present in the posterior margin. The smallest specimen (MCN.P.1225; Fig. 3c) is 11.1 mm long, 7.8 mm wide, and 3.8 mm thick and the larger ones (MCN.P.1226) are 11.2 mm wide, and 6.2 mm thick. Regarding movable osteoderms, all specimens have large foramina in the anterior-central region also surrounding the anterior portion of the main figure. The surface is smooth and the anterolateral figures are convex and acute anterior and posteriorly (MCN.P.1228; Fig. 3d). The main figure is elongated and lageniform with large foramina (around 0.8 mm) placed on both sides and along the lateroposterior edge asymmetrically placed. The longitudinal keel is long, high, and narrow, reaching the posterior edge of the osteoderm. The posterior margin of the osteoderm has eight piliferous foramina. The movable osteoderm (MCN.P.1228) is 14.4 mm long, 5.5 mm wide, and 2.8 mm thick. The semimovable osteoderm (MCN.P.1227) is 11.4 mm long, 5.8 mm wide, and 3.4 mm thick.

Remarks: The osteoderms here identified as Astegotheriini take into account the presence of a main figure with a short neck, lateral figures in both sides, and presence of large foramina along the lateral sides of the main figure. The movable osteoderm is incomplete, lacking the anterior region. When compared to other dasypodids, the Guabirotuba specimen resembles Pseudostegotherium Ameghino, 1902, from Gran Barranca, Patagonia (Barrancan?-Colhuehuapian, following Carlini et al. 2010), in the presence of large foramina surrounding the neck of the main figure, a smooth external surface, scarce foramina placed in the lateral sides of the main figure (which are more regular in size and most numerous in stegotheriines), and a long and narrow keel in movable osteoderms. However, the osteoderms of the Guabirotuba Formation differ from Pseudostegotherium in having larger and thicker osteoderms; furthermore, in buckler osteoderms, the foramina increase in size from the posterior to the anterior. The foramina in a movable osteoderm are greater in number (more than 15) than in typical Astegotheriini as, for example, in Stegosimpsonia Vizcaíno, 1994 (Carlini et al. 2010). The Itaboraian Riostegotherium yanei Oliveira and Bergqvist, 1998, also presents the foramina forming an arch delimiting the main figure anteriorly in the buckler osteoderm although even greater in number.

Subfamily Euphractinae Winge, 1923

Tribe “Utaetini” Simpson, 1945

Utaetus Ameghino, 1902

Utaetus sp.

(Fig. 3e)

Type species: Utaetus buccatus Ameghino, 1902

Temporal distribution: Late middle Eocene, Barrancan (Ciancio and Carlini 2008; Carlini et al. 2010; Gaudin and Croft 2015).

Referred material: MCN.P.1231(1–7), seven movable osteoderms all from the same individual.

Description: Movable osteoderms MCN.P.1231(2) with generally four large foramina symmetrically placed in the vertices of a square area on the anterior region of the main figure and these foramina are subequal in size, but some osteoderms could present less foramina (two or three) always positioned on the same area. The external surface is quite punctuated and the articular area is short with a marked step. The median keel is narrow and very low. A typical osteoderm MCN.P.1231(2) measures 21.5 mm long, 9.0 mm wide, and 3.0 mm thick (Fig. 3e).

Remarks: The Utaetus found in Guabirotuba Formation differ from other species, such as ?U. deustus which is much larger (30.0 to 40.0 mm long, and 15.0 mm wide), and has a more rugose external surface (Carlini et al. 2010); differs from Utaetus buccatus Ameghino, 1902, in having a more punctuated external surface, but the Guabirotuba Utaetus is morphologically closer to U. buccatus from the Barrancan levels in Patagonia (Carlini et al. 2010) in having a similar size and large foramina in the anterior area of the main figure (generally four large foramina). Comparison with U. argos and U. laxus are not possible as both are defined only based on buckler osteoderms.

Tribe Eutatini Bordas, 1933

Meteutatus Ameghino, 1902

Meteutatus sp.

(Fig. 3f)

Type species: Meteutatus lagenaformis (Ameghino, 1897)

Temporal distribution: Late middle Eocene to late Oligocene, Barrancan to Deseadan SALMAs (Carlini et al. 2010).

Referred material: MCN.P.1246, one buckler osteoderm.

Description: The osteoderm is rectangular measuring 14.4 mm long, 7.8 mm wide, and 3.8 mm thick (Fig. 3f). The two anterior figures are sub-rectangular and subequal in size. The lateromedial figures are trapezoidal, smaller than the anterior ones, and also smaller than the posterolateral ones. The central figure is elongated and add to the lateroposterior figures to compose a lageniform main figure. The central figure is straight posteriorly (pointed) reaching the posterior margin of the osteoderm. The posterolateral figures are sub-retangular in shape. On the posterior edge, the osteoderm presents a furrow visible posteriorly and dorsally, with at least nine piliferous foramina separated by septa.

Remarks: The material from Guabirotuba Formation is assigned to Meteutatus, which also occurs from late middle Eocene to early Oligocene of Patagonia (Carlini et al. 2010). The derived features diagnosed by Carlini et al. (2009) for Meteutatus are present on the material described herein: fixed osteoderms with lageniform (bottle-shaped) main figure, with the neck placed centrally; this figure widens posteriorly, reaching the lateral borders of the osteoderm and thus making up the entire posterior portion; presence of a pair of big anterior figures, and a pair of lateral figures occurs on both sides of the neck of the central figure; and finally the posterior edge is occupied by a straight furrow that is dorsally visible. Meteutatus sp. from Guabirotuba Formation can be distinguished from all Patagonian species in having a less prominent posterior piliferous system, which is less open to the external surface. When compared with Barrancatatus Carlini et al., 2010 (a closely related genus to Meteutatus) from the Tinguirirican and Deseadan faunas, Meteutatus sp. from Guabirotuba presents the external surface less rugose and the piliferous sulcus separated by few septa instead of by many small and thin septa limiting thin conduits in Barrancatatus that indicates abundant pilosity (Carlini et al. 2010).

Tribe Euphractini Winge, 1923

Parutaetus Ameghino, 1902

Parutaetus sp.

(Fig. 3g-j)

Temporal distribution: From Barrancan (Ciancio and Carlini 2008), Fauna de “El Nuevo” and “El Rosado” (Carlini et al. 2010) and Mustersan to Tinguirirican (Ciancio et al. 2016).

Referred material: MCN.P.1240, 1241, 1242, 1243, 1249, complete buckler osteoderms; MCN.P.1244, 1245, incomplete buckler osteoderms; MCN.P.1250 (Fig. 3i), 1251, 1252, 1253, incomplete movable osteoderms.

Description: MCN.P.1240 (Fig. 3h) is a buckler osteoderm rectangular in outline, relatively thick, and 14.6 mm long, 8.9 mm wide, and 4.0 mm thick. The external surface is smooth and punctuated by small foramina. Presents two anterior figures separated by swallow straight sulcus that is posteriorly limited by an arched sulcus composed of two large foramina laterally interspersed with at least three smaller foramina centrally, irregularly distributed within the sulcus. The anterolateral figures are triangular in shape with acute expansions that almost reach the posterior corner. The main figure is bell-shaped and the central keel is teardrop-shaped with the bulbous portion anteriorly placed and a small portion of the keel reaches the posterior margin. The posterior margin has six dorsally placed piliferous foramina. MCN.P.1243, 20.6 mm long, 13.4 mm wide, and 6.7 mm thick (Fig. 3g), is a large buckler osteoderm that presents two anterior large, unequal, and convex trapezoidal figures separated by a pronounced sulcus. Presents a bell-shaped main figure with a bulbous keel that is shortened and does not reach the posterior margin of the osteoderm, which present five piliferous foramina. MCN.P.1250 is a large movable osteoderm lacking only the distal region (Fig. 3i). The external surface is smooth, and the lateral articular surfaces are poorly serrated. The anterior articulation surface is broad and slightly narrow anteriorly. The medial figure is rounded, elongated, and is delimited by two longitudinal wide sulci. The lateral figures present a transverse and slightly oblique sulcus.

Remarks: The Guabirotuba Parutaetus was identified following Carlini et al. (2009) on the basis of a combination of some characters including the presence of large and polygonal (trapezoidal) anterior figures, central figure (or keel) shortened and teardrop-shaped, and surfaces of all figures convex. In relation to the Patagonian, northwestern Argentinean and Chilean species, the Brazilian Parutaetus is larger in size, presenting five or six piliferous foramina unlike only two in P. chilensis, two to four as in P. chicoensis, and two to five as in P. punaensis. Another Patagonian species, P. clusus, also presents five to six foramina, but is smaller in size in relation to the Brazilian Parutaetus (Ameghino, 1902).

Euphractinae indet.

(Fig. 3k, l)

Temporal distribution: From Barrancan to Recent (Ciancio et al. 2013).

Referred material: MCN.P.1248, one buckler osteoderm; MCN.P.1247, an incomplete movable osteoderm.

Description: Buckler osteoderm (MCN.P.1248) is sub-rectangular in outline. The surface is almost smooth with shallow rugosities and several small foramina (Fig. 3k). The two anterior figures are convex and separated by a shallow sulcus. The anterolateral figures are triangular but do not reach the posterior corner. The central figure is low, elongated, and delimited by two rows of small foramina. The movable osteoderm (Fig. 3l) presents a smooth external surface with a wide articular area. The external surface is smooth with shallow rugosities and the main figure is delimited by two shallow sulci.

Remarks: When compared to other euphractines described for the Eocene or Oligocene, this Guabirotuba armadillo resembles Utaetus and Parutaetus, but differs from the known species in having a shallow central keel and not forming a teardrop-shape.

Order NOTOUNGULATA Roth, 1903

Family Interatheriidae Ameghino, 1897

Subfamily Notopithecinae Simpson, 1945

Gen. et sp. indet.

(Fig. 4a-d)
Fig. 4

Micro CT-scan images of South American native ungulates from Guabirotuba Formation. a MCN.P.1255, Interatheriidae, gen. et sp. indet., occlusal view of right m2; b MCN.P.1254, Interatheriidae, gen. et sp. indet., occlusal view of left m3; c MCN.P.1253, Interatheriidae, gen. et sp. indet., occlusal view of right p4; d MCN.P.1256, Interatheriidae, gen. et sp. indet., occlusal view of left mandible with m3 talonid; e MCN.P.1257, Oldfieldthomasiidae, gen. et sp. indet., occlusal view of incomplete mandible with p2-m1; f MCN.P.1258, Astrapotheria, gen. et sp. indet., occlusal view of right M1, g MCN.P.1258, Astrapotheria, gen. et sp. indet., labial view of right M1. Scale bar =5 mm

Temporal distribution: The Notopithecinae (sensu Vera 2016) occurs in middle-late to late Eocene, Barrancan to Mustersan SALMAs (García-López and Babot 2015; Vera 2016).

Referred material: Four specimens that probably belong to different species. MCN.P.1253, right dentary fragment with root of p3 and p4; MCN.P.1254, left dentary fragment with m3; MCN.P.1255, right dentary fragment with m2; MCN.P.1256, left dentary fragment with m3 talonid and their respective root.

Description: All teeth are brachydont and bilobated with the trigonid separated from talonid by deep labial and lingual sulci (Fig. 4a-d). MCN.P.1253 exhibits a trigonid larger than talonid, an incipient paralophid, an almost straight protolophid, and a postmetacristid orientated distally (Fig. 4c). The molars show evident metacristids (Fig. 4a–d). MCN.P.1254 presents trigonid and talonid subequal, its paralophid is short and parallel to the metalophid, the protolophid is slightly labially curved, the hypolophid is concave, and the mesial extension of the entolophid is small. The morphology of MCN.P.1254 is similar to MCN.P.1255 but the talonid is slightly smaller than the trigonid, the entoconid is projected lingually, and the hypoconulid is more distally prominent (Fig. 4b). MCN.P.1256 shows a distolingual portion of the metalophid, an entoconid placed parallel to the metalophid, and a hypolophid located distally (Fig. 4d).

Remarks: Among typothere notoungulates, the specimens of Guabirotuba Formation differ from Interatheriidae, Interatheriinae (e.g., Santiagorothia Hitz et al., 2000, and Proargyrohyrax Hitz et al., 2000) in having a brachydont dentition. The premolars presents the postmetacristid and talonid smaller than the trigonid and the molars show a larger mesial extension of the entolophid but does not reach the trigonid, a feature that characterizes the Notopithecinae (sensu Vera 2016). However, the Guabirotuba specimens exhibit a small paralophid in the premolars and molars, differently to all known notopithecines.

Family Oldfieldthomasiidae Simpson, 1945

Gen. et sp. indet.

(Fig. 4e)

Temporal distribution: Early Eocene to late Oligocene, Itaboraian to Deseadan SALMAs (Tejedor et al. 2009; Ubilla et al. 1999).

Referred material: MCN.P.1257, incomplete mandible with right p2-m1.

Description: The specimen presents a completely fused symphysis (Fig. 4e). There is no visible foramen on the lateral surface. The posterior region of the symphysis reaches the level below the anterior root of p2. The dentition is brachydont and without diastema. The p2 presents a trigonid and a small talonid with a cuspid (entoconid) situated distolabially. The morphology of p3 is similar to p2 but p3 presents a bigger metalophid and talonid. The morphology of p4 is similar to m1, is slightly smaller than m1, and exhibits a talonid longer than trigonid. The trigonid and talonid of m1 are subequal in size; the tooth exhibits a small paraconid situated mesially, a tranverse metalophid, and a small accessory cusp just below the metaconid. The talonid shows a conical entoconid distally placed. The hypoconulid of the m1 is the smallest cuspid in the distal edge of talonid, and the hypolophid is contiguous with the oblique cristid.

Remarks: MCN.P.1257 was previously assigned to Henricosborniidae (Silva et al. 2014), but this specimen presents a short paralophid connected with anterolingual cingula, entoconid separate to metalophid and without form fossetids between trigonid and talonid that are characteristics of the Oldfieldthomasiidae (Montalvo and Bond 1998).

Order ASTRAPOTHERIA Lydekker, 1894

Gen. et sp. indet.

(Fig. 4f-g)

Temporal distribution: Early Eocene-late Miocene, Itaboraian to Laventan (Soria and Powell 1982; Antoine et al. 2016b).

Referred material: MCN.P.1258, a right M1.

Description: The tooth is brachydont and has three roots (Fig. 4g). The M1 exhibits a rectangular outline in occlusal view, the parastyle is well projected mesially, and the paracone fold is situated near the central part of ectoloph, adjacent to the metacone fold (Fig. 4f). The protoloph is oblique, almost reaches the lingual cingulum, and ends in a large protocone cusp while the metaloph is short and straight. On the distolingual area the hypoflexus is small, directed obliqualy and labially, and the hypocone is very low.

Remarks: MCN.P.1258 shows a smooth labial fold of metacone and due to wear it is not possible to ascertain if there were a crista and crochet. On the other hand, it differs from Tetragonostylops Paula Couto, 1963, Albertogaudrya Ameghino, 1901, and Astraponotus Ameghino, 1901, in having clearly rectangular tooth morphology in occlusal view, in the bigger parastyle, and protoloph that reaches the lingual cingulum.

Infraclass METATHERIA Huxley, 1880

Order SPARASSODONTA Ameghino, 1894

Nemolestes Ameghino, 1902

Nemolestes, sp. indet.

(Fig. 5a-b)
Fig. 5

Micro CT-scan images of metatherians from Guabirotuba Formation. a MCN.P.1259, Nemolestes, sp. indet., lateral view of incomplete left dentary with p2-m3; b MCN.P.1259, Nemolestes, sp. indet., occlusal view of incomplete left dentary with p2-m3; c MCN.P.1260, Palaeothentoidea, gen. et sp. indet., occlusal view of p3 and m1; d MCN.P.1261, Argyrolagoidea, gen. et sp. indet., lateral view of an incomplete left dentary with m2; e MCN.P.1261, Argyrolagoidea, gen. et sp. indet., occlusal view of an incomplete left dentary with m2. Scale bar =5 mm

Type species: Nemolestes spalacotherinus Ameghino, 1902

Temporal distribution: Early to middle Eocene, Itaboraian to Barrancan SALMAs (Forasiepi 2009).

Referred specimen: MCN.P.1259, an incomplete left dentary with p2-m3.

Description: The dentary is very deep below the anterior alveolus of m3 (Fig. 5a). The symphysis extends posteriorly to a point below the anterior root of p3. Two mental foramina are present; the anterior is placed below the canine and the p2 while the posterior one is below the anterior edge of m1. The anterior foramen is larger than the posterior. Regarding the premolars, p2 and p3 are two rooted, with the p3 slightly longer than p2. The m1 is much worn out, and is slightly shorter than m2. The m2 has a large trigonid, with a large paraconid and a small metaconid (Fig. 5b). The talonid is very short with small entoconid, hypoconid, and hypoconulid. The hypoconulid is twinned with the entoconid. The postcingulid descends from the hypoconulid to the crown base of the hypoconid, terminating at the posterolabial corner of tooth. The m3 differs from m1 in having a trigonid larger, with bigger protoconid and paraconid.

Remarks: The presence of trigonid, talonid tricuspidated, and a big postcingulid suggests affinities with basal sparassodonts (Forasiepi et al. 2014) such as Patene Simpson, 1935, and Nemolestes Ameghino, 1902. Patene is from the early Eocene of Brazil, middle Eocene of Argentina, and late Eocene?-early Oligocene of Peru, whereas Nemolestes is from the Barrancan of Patagonia (Simpson 1948; Goin and Candela 2004). The genus was tentatively identified for Itaboraí and Paso del Sapo (cf. Nemolestes, Marshall et al. 1983, 1997; Tejedor et al. 2009). Another basal taxon is Procladosictis Ameghino, 1902, from Barrancan and Mustersan SALMAs of Argentina (Woodburne et al. 2014b). The Guabirotuba specimen was first assigned to Patene (Dias et al. 2014); however, it presents a bigger protoconid and a smaller metaconid than Patene, both features related to carnivory specialization (Marshall 1981; Oliveira and Goin 2006). Comparison with Procladosictis is more difficult because the holotype is based on the upper dentition, but judging by features of a lower molar referred by Simpson (1948: 45), Procladosictis differs from the Guabirotuba sparassodont in having a small metaconid and a narrow-basined talonid. The Guabirotuba specimen (MCN. P.1259) shares with Nemolestes a big metaconid and a small protoconid, which justifies the assignment to Nemolestes.

Order PAUCITUBERCULATA Ameghino, 1894

Superfamily Palaeothentoidea Sinclair, 1906

Gen. et sp. indet.

(Fig. 5c)

Temporal distribution: From the late-middle Eocene to late Miocene, Barrancan to Laventan (Goin and Candela 1998; Zimicz 2012; Abello 2013).

Referred specimen: MCN.P.1260, an incomplete right dentary with p3 and m1.

Description: On the lateral surface the dentary presents a foramen (probably the posterior mental foramen) placed below and between the two roots of the m1. The p3 is low-crowned with quite developed crests on the posterolabial and posterolingual areas, and an anterior cuspule is present (Fig. 5c). The m1 is low-crowned, with trigonid and talonid subequal in size. The anterocingulid is very short, not reaching the lateral area of the tooth. The protoconid is large, basally wide, occupying almost the whole labial half of the trigonid, and posteriorly presents a rounded crest. The metaconid is transversely aligned with the protoconid. The paraconid is slightly smaller in size than the metaconid and both are placed close to each other. The juncture of the posparacristid and the preparacristid forms a right angle, while the union of postprotocristid and the postmetacristid forms an acute angle. The talonid is short, subequal in width to the trigonid, and has a large, laterally compressed entoconid. A postentocristid is present, running labially and ending in the talonid. The hypoconulid is very small, while the hypoconid is robust, basally wide, and larger than the entoconid.

Remarks: In overall features, this specimen resembles some members of Palaeothentoidea such as Pilchenia Ameghino, 1904, Perulestes Goin and Candela, 2004, and Sasawatsu Goin and Candela, 2004, from the late Eocene to late Oligocene of Argentina and Peru (Goin and Candela 2004; Abello 2013). The Guabirotuba specimen (MCN.P.1260) shares some derived features with Palaeothentoidea such as a markedly different enamel thickness between the lateral and occlusal molar faces, presence of a crest-like expansion posterior to the protoconid, and presence of postentocristid (Abello 2013). When compared with members of palaeothentoids, MCN.P.1260 differs from pichipilids in not having any of the synapomorphies listed for p3 and m1 by Abello (2013). Direct comparison can be performed only with Perulestes and Pilchenia, which have m1 known. The m1 here described shares with Perulestes only a protoconid much higher than metaconid, while the paraconid is more prominent in MCN.P. 1260. Only the moderately sized paraconid of the Pilchenia clade (Abello 2013) is present in the Guabirotuba specimen. MCN.P.1260 exhibits combined features that are distinct in relation to abderitids and palaeothentids, including the absence of anterior lingual crests on p3, presence of anterobasal and posterobasal cingulids on p3, on m1 a metaconid that is transversely aligned with the protoconid, and a talonid that is near equal in width and length with the talonid.

Order POLYDOLOPIMORPHIA Ameghino, 1897

Superfamily Argyrolagoidea Ameghino, 1904

Gen. et sp. indet.

(Fig. 5d-e)

Temporal distribution: From Eocene to Pliocene, Vacan to Marplatan SALMAs (Cerdeño et al. 2008; López 2010; Zimicz 2011; Goin et al. 2016).

Referred specimen: MCN.P.1261, an incomplete left dentary with small portion of the entoconid of the m2 and complete m3.

Description: MCN.P.1261 has high crowns; the m3 trigonid is slender and much shorter than the talonid, with a big metaconid and protoconid, whereas the paraconid is vestigial (Fig. 5d-e). The metaconid is mesially displaced in relation to protoconid. The entoconid is very big and placed mesially in relation to hypoconid. The hypoconulid is robust and is placed posterolingually to the entoconid. The hypoconid is the tallest cusp of the tooth. Anterior to hypoconid there is a small cuspule, the “ectostylid.” The teeth present distinct roots and the posterior root is longer than the anterior one.

Remarks: The specimens are morphologically related to basal argyrolagoids such as Praedens Goin et al., 2010, Klohnia Flynn and Wyss, 1999, and Epiklohnia Goin et al., 2010, because of the presence of a neocusp (“ectostylid”) (Goin et al. 2010) and the high-crowned condition of lower molars suggest a closer relationship with Klohnia and Epiklohnia, which are formally included within the Argyrolagoidea (Goin et al. 2010). The Guabirotuba argyrolagoid is distinct by its generalized pattern with the trigonid, including the pre- and postprotocristid, a non- anteroposteriorly compressed molar, combined with some specialized features such as a strong pre-entocristid, and a small cuspule placed between the hypoconid and the hypoconulid.

Discussion

The age of the Guabirotuba Fauna and its implication on the South American mammalian diversity is discussed.

The diversity and time distribution of cingulates in Gran Barranca (Patagonia), where the Eocene-Oligocene transition is well documented, includes the Asthegoteriini, Stegotheriini, “Utaetini”, Eutatini, and Euphractini. During the Eocene a decrease in diversity and a relative abundance of the Astegotheriini is observed, and in the early Oligocene an increase in diversity of Euphractinae (Euphractini + Eutatini) with a pronounced pilosity, probably in response to a colder climate is recorded (Carlini et al. 2010; Ciancio et al. 2013). The Eocene cingulates of northwest Argentina are represented by “Utaetini” (cf. Utaetus), Euphractini (Parutaetus), Astegotheriini (Prostegotherium, cf. Astegotherium, Parastegosimpsonia), and an exclusive roll of endemic cingulates (Punatherium, Pucatherium, Lumbreratherium) that are recorded at Geste, Quebrada de Los Colorados, Casa Grande, and Lumbrera formations (Powell et al. 2011; Ciancio et al. 2016; Herrera et al. 2016). Some taxa from northwest Argentina also occur in Patagonian faunas (Utaetus, Parutaetus, Prostegotherium) and only one occurs in tropical areas (Parastegosimpsonia). In low latitudes, such as Contamana and Santa Rosa, during the Eocene there are records of Astegotheriini (Stegosimpsonia, Parastegosimpsonia) and cingulates of indeterminate family (Yuruatherium, Eocoleophorus), and to date specimens of Euphractinae are not recorded (Ciancio et al. 2013; Antoine et al. 2016b).

The cingulates from Guabirotuba Formation include two medium-large sized taxa, Machlydotherium and Proeocoleophorus, both related with two mid-low latitudes forms (Eocoleophorus from Brazil, Bolivia, and Peru; Yuruatherium tropicalis from Peru) and at least one of high latitudes (Yuruatherium intortum). The Guabirotuba cingulates also includes Utaetus, a “Utaetini” that occurs in Patagonia and northwest Argentina; Meteutatus, which is recorded in Patagonia, Parutaetus also recorded in Patagonia and northwest Argentina, an endemic Astegotheriini, and an indeterminate Euphractini. This unique composition exhibits a mosaic of taxa related to faunas from high, mid, and low latitudes that comprise a temporal interval from Barrancan to Deseadean. However, the presence of the Proeocoleophorus, which has plesiomorphic characteristics in relation to Eocoleophorus from Deseadan, Utaetus with a record restricted to Barrancan, Parutaetus and Machlydotherium both with distribution beginning in the Barrancan is considered indicative of Barrancan SALMA (late middle Eocene) for the Guabirotuba Fauna.

The increase of hypsodont native ungulates during the Barancan-Tinguirirican interval is documented in the high-latitude localities of Gran Barranca, at El Nuevo (Barrrancan), El Rosado (Mustersan), La Cancha (Tinguirirican), and La Cantera (post-Tinguirirican or Deseadan) (López et al. 2005, 2010; Madden et al. 2010; Reguero and Prevosti 2010; Reguero et al. 2010; Ribeiro et al. 2010). From Vacan to Mustersan the record of native ungulates from northwestern Argentina (mid-latitudes) presents a high number of endemic genera and the absence of hypsodonty (Carbajal et al. 1977; López 1997; Reguero et al. 2008; Powell et al. 2011; García-López and Babot 2015; Ciancio et al. 2016). The faunas of Contamana and Santa Rosa are the only record of mammals throughout late-middle Eocene to early Oligocene from low latitudes in South America. The native ungulates recorded in Contamana Eocene localities are brachydont and those from Oligocene are hypsodont, even though the native ungulates from Contamana during this interval consist mainly of isolated teeth or tooth fragments (Antoine et al. 2016a, 2016b). The native ungulates from Santa Rosa locality suggest a time range from Tinguirirican to Deseadan based on the presence of only hypsodont forms (Shockey et al. 2004). As discussed above, during the Eocene there is a prevalence of brachydont native ungulates, whereas in the Oligocene this proportion is inverted, with prevalence of hypsodont forms, and it seems to be independent of latitude throughout South America.

All the specimens assigned to Interatheriidae from Guabirotuba Fauna have brachydont dentition and a mesial extension of the entolophid on the molars that does not reach the metaconid, which are diagnostic characteristics of the Notopithecinae, with a temporal distribution from Barrancan to Mustersan (sensu Vera 2016). The oldfieldthomasiid specimen from Guabirotuba Formation also presents brachydont dentition and is similar, in occlusal view, to Oldfieldthomasia Ameghino, 1901, and Maxschlosseria Ameghino, 1901, typical genera from Riochican and Vacan of Patagonia (Simpson 1967). Oldfieldthomasiidae (sensu Simpson 1945) are small- to moderate-sized ungulates with generalized crown morphology of basal members of Typotheria. Recent studies suggest that Oldfieldthomasiidae is a paraphyletic group (Billet 2011; García-López and Babot 2015; Vera 2016). Their temporal distribution is from Itaboraian (early Eocene) of Brazil and Patagonia (Pascual and Ortiz-Jaureguizar 1992) to Deseadan (late Oligocene) of Fray Bentos Formation in Uruguay (Ubilla et al. 1999). The astrapothere from Guabirotuba Fauna is comparable with Tetragonostylops from Itaboraian of Brazil, with Argentinean Albertogaudrya from Casamayoran (sensu Simpson 1967), and Astraponotus from Mustersan, but it is more rectangular in occlusal outline and has a more prominent parastyle. The Guabirotuba Fauna does not share any native ungulate genera with any South American Paleogene fauna; however, all ungulates recovered from Guabirotuba Formation are brachydont even so, in some cases hypsodonty is incipient. The Guabirotuba native ungulates have morphological affinities with genera from Vacan to Mustersan instead of Tinguirirican. According to Kay et al. (1999) the appearance of a large number of hypsodont notoungulates occurred between 36 and 32 Myr (late Eocene-early Oligocene), and the Tinguiririca Fauna (early Oligocene) is the oldest fauna dominated by hypsodont herbivores in South America (Pascual and Ortiz-Jaureguizar 2007; Flynn et al. 2003). Reguero et al. (2010) also showed the dominance of brachydont notoungulates for the Mustersan SALMA (late Eocene). Considering that all known native ungulates of Guabirotuba Fauna are brachydont and with an evolutionary degree related to Eocene taxa from other faunas, this also supports a pre-Oligocene age.

The Guabirotuba metatherians include a polydolopimorphian morphologically related to basal argyrolagoids such as Klohnia and Epiklohnia, but representing distinct taxon that could be related to early diversification of argyrolagoids during the faunal turnover of Eocene-Oligocene transition (Goin et al. 2010). Similarly, the new paucituberculatan palaeothentoid from Guabirotuba seems to be related to the rapid radiation of paucituberculatans that documents the emergence of ?caenolestids, pichipilids, and paleothentids (Goin et al. 2010). The presence of a basal sparassodont metatherian Nemolestes is additional evidence for the age of the Guabirotuba Fauna (Fig. 6) as the youngest and most reliable known record of this genus is Barrancan (Forasiepi 2009; Woodburne et al. 2014b) and the records for Paso del Sapo and Itaboraí are doubtful (Marshall 1981; Tejedor et al. 2009).
Fig. 6

Stratigraphic chart for Eocene/Oligocene with SALMAs and a proposal for Guabirotuba Formation age. Dashed line and question marks in the Nemolestes distribution represents record of cf. Nemolestes. SALMAs based on Woodburne et al. (2014b)

From a trophic perspective, the Guabirotuba metatherians include Nemolestes, which is a medium-size hypercarnivorous form (sensu Zimicz 2014) with a generalized molar pattern compatible with more forested adapted species from the early and middle Eocene, such as Procladosictis and Patene, the last one reaching early Oligocene. Regarding the record of an argyrolagoid, the morphologically related forms such as Klohnia and Praedens have molar features related to feeding habits that included either more abrasive items, or distinct vegetal structures such as seeds, hard fruits (or fruits covered by hard pericarpia), or a combination of them (Goin et al. 2010). This adaptation is related to development of a rodent-like molar pattern and additions of neocusps such as “ectostylid,” “entostylid,” “epiconule,” and an “epiconular shelf” (Goin et al. 2010). Although the argyrolagoid recorded in Guabirotuba presents an “ectostylid” and high crowned molars, the “unilateral hypsodonty” is not so evident in the available specimen. Therefore, this tooth morphology in the Guabirotuba argyrolagoid is much less specialized than in Klohnia, Praedens, and Epiklohnia, suggesting a diet much less abrasive than in these early Oligocene taxa. The record of a palaeothentoid in Guabirotuba Formation with dental features including low and inflated cusps, as well as reduced cristae, is suggestive of a frugivorous diet.

The biostratigraphic distribution of the Guabirotuba Formation mammalian taxa forms a concurrent-range biozone of Barrancan age (Fig. 6) based on temporal distribution of: the cingulates Utaetus (Barrancan), Machlydotherium (Barrancan to Tinguirirican), Meteutatus (Barrancan to Deseadan); the ungulates Notopithecinae (Barrancan to Mustersan), Oldfieldthomasiidae (Itaboraian to Deseadan), and Astrapotheria (Itaboraian to Laventan); and the metatherians Nemolestes (Itaboraian to Barrancan), palaeothentoids (Barrancan to Laventan), and argyrolagoids (Vacan to Marplatan). The presence of Utaetus sp. is considered an important data for the determination of the Guabirotuba Formation age, as this genus occur only in the Barrancan. The occurrence of Nemolestes in the Guabirotuba Fauna constitutes another element of correlation with the Barrancan (Woodburne et al. 2014b), as the occurrences of Nemolestes for Itaboraí and Paso del Sapo are uncertain (Tejedor et al. 2009), and also, no occurrence of Nemolestes for post-Barrancan age is known.

The combined evidence available suggests a Barrancan age (late middle Eocene) for the Guabirotuba Fauna (Fig. 6). However, as indicated by dashed lines and question marks in Fig. 6, it is possible that the lower limit could be extended to the gap between Vacan and Barrancan, which is less probable because most taxa distribution is limited to Barrancan, and the upper limit could be extended to Mustersan, but still pending on more accurate taxonomic definitions and other chronological data.

A Tinguirirican age (early Oligocene) is less probable, because it is marked by a high proportion of hypsodont mammals (mainly notoungulates), which coincides with a sudden fall of global temperatures (Woodburne et al. 2014b). In Guabirotuba Fauna only brachydont ungulates occur, so a Tinguirirican age (early Oligocene) is not supported (Woodburne et al. 2014b).

The Guabirotuba Fauna is geographically placed at mid-latitudes and besides the endemic taxa (Proeocoleophorus), presents several taxa shared with the high-latitude Patagonian faunas (Utaetus, Parutaetus, Meteutatus, Machlydotherium, Nemolestes) and some taxa shared with mid-latitude faunas of northwest Argentina (Utaetus, Parutaetus), which shows that Guabirotuba Fauna presents a closer relationship to Patagonian and northwest Argentinean faunas than with Santa Rosa and Contamana mammal associations from Peruvian Amazonia. Until the moment, few taxa of higher taxonomic level are shared with low-latitude faunas of Contamana and Santa Rosa (Interatheriidae, Astrapotheria, Palaeothentoidea), and accurate taxonomy will clarify the relation of Guabirotuba Fauna with other low-latitude faunas.

In relation to the origin of the basin, historically the Curitiba Basin has been considered as belonging to the Cenozoic continental rift system of southeastern Brazil (Riccomini et al. 2004). Later, Zalán and Oliveira (2005) excluded the Curitiba Basin of the continental rift based on the smaller magnitude of its grabens. However, the smaller scale of Curitiba Basin grabens in comparison with other bigger ones is not evidence that it does not belong to the rift system, and the attribution of an Eocene age for the Guabirotuba Formation reinforces the Curitiba Basin relation to the Cenozoic continental rift of southeastern Brazil as already assumed by several authors (e.g., Almeida 1976; Salamuni et al. 2003; Riccomini et al. 2004; Liccardo and Weinschütz 2010; Lima et al. 2013).

Conclusion

A new Paleogene land mammal fauna is recorded for the Guabirotuba Formation, composed of Cingulata, Notoungulata, Astrapotheria, and Metatheria. The cingulates include Proeocoleophorus carlinii, gen. et sp. nov., Machlydotherium sp., Astegotheriini, gen. et sp. indet., Utaetus sp., Meteutatus sp., Parutaetus, sp. indet., and Euphractini indet. The native ungulates are represented by Interatheriidae, gen. et sp. indet., Oldfieldthomasiidae, gen. et sp. indet., and Astrapotheria, gen. et sp. indet. The metatherians are composed of Nemolestes, sp. indet., Palaeothentoidea, gen. et sp. indet., and Argyrolagoidea, gen. et sp. indet.

The presence of only brachydont ungulates is evidence for a pre-Oligocene age for the Guabirotuba Formation. The occurrence of the cingulate Utaetus and the presence of the basal sparassodont Nemolestes are evidence for a late middle Eocene interval (Barrancan age) for the Guabirotuba Fauna.

The new cingulate Proeocoleophorus carlinii presents plesiomorphic characteristics in relation to Eocoleophorus glyptodontoides including evidence of low pilosity, which matches with the predominant climate conditions presumed for the Eocene age at South American mid-latitudes.

As Utaetus and Proecoleophorus were found in distinct levels of the fossil-bearing site, a long term time-averaging seems unlikely.

The Guabirotuba assemblage is a new land mammal fauna that represents an important discovery for the study of South American mammalian evolution and can provide new data on paleobiogeography and paleoecology of this continent.

Notes

Acknowledgements

The authors thank CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), which provided financial support to the project (process number 486692/2012-4), Doctoral Grant to David D. da Silva (process number 140772/2012-0), grant to Ana M. Ribeiro (process number 312085/2013-3), Édison V. de Oliveira (process number 303741/2013-9), and Luiz A. Fernandes (PQ process number 303802/2013-8), and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for providing Master’s Grant to Renata F. Cunha. The authors would like to thank the Natural Science Museum - Federal University of Paraná for providing infrastructure and facilities for the study of the specimens. We thank Pierre-Oliver Antoine and Francois Pujos who invited us and coordinated this special issue; Sibelle T. Disaró, Leonardo Kerber, Ana T. B. Guimarães, and Rafael C. da Silva who gave us valorous suggestions. We also thank to Ricardo L.V. Queiroz and Andrea A. Doris for helping in the English revision, Thiago G. da Silva (Analysis Laboratory of Minerals and Rocks – LAMIR –Federal University of Paraná) for Micro-CT scan images, and Eduardo S. Suzuki for their assistance in photographs preparation. The authors are grateful to Antonio Liccardo and Luiz C. Weinschütz for their pioneer works, and Victor E. Pauliv, Marcel B. Lacerda, Wagner L. Gogola, Thiago Carlisbino, Orestes Jarentchuk Junior, and other colleagues, students, and friends that helped in the fieldwork.

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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • Fernando A. Sedor
    • 1
    Email author
  • Édison V. Oliveira
    • 2
  • David D. Silva
    • 3
  • Luiz A. Fernandes
    • 4
  • Renata F. Cunha
    • 4
  • Ana M. Ribeiro
    • 5
  • Eliseu V. Dias
    • 6
  1. 1.Museu de Ciências NaturaisCampus do Centro Politécnico, Setor de Ciências Biológicas - Universidade Federal do ParanáCuritibaBrazil
  2. 2.Departamento de GeologiaUniversidade Federal de PernambucoRecifeBrazil
  3. 3.Programa de Pós-graduação em GeociênciasUniversidade Federal do Rio Grande do SulPorto AlegreBrazil
  4. 4.Departamento de GeologiaUniversidade Federal do ParanáCuritibaBrazil
  5. 5.Fundação Zoobotânica do Rio Grande do Sul, FZBRSPorto AlegreBrazil
  6. 6.UNIOESTE - Campus de Cascavel, CCBS, Laboratório de Geologia e PaleontologiaUniversidade Estadual do Oeste do ParanáCascavelBrazil

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