Cranial bones and atlas of titanosaurs (Dinosauria, Sauropoda) from Late Cretaceous (Bauru Group) of Uberaba, Minas Gerais State, Brazil

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Journal of South American Earth Sciences xxx (2015) 1e7

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Journal of South American Earth Sciences

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Cranial bones and atlas of titanosaurs (Dinosauria, Sauropoda) fromLate Cretaceous (Bauru Group) of Uberaba, Minas Gerais State, Brazil

Agustín G. Martinelli a, b, *, Thiago da Silva Marinho a, c, Leonardo S. Filippi d,Luiz Carlos Borges Ribeiro a, Mara Lúcia da Fonseca Ferraz a, Camila Lourencini Cavellani a,Vicente de Paula Antunes Teixeira a

a Centro de Pesquisas Paleontol�ogicas L. I. Price, CCCP/UFTM, 38001-970, BR-262, Km 784, Peir�opolis, Uberaba, MG, Brazilb Departamento de Paleontologia e Estratigrafia, Instituto de Geociencias, Universidade Federal de Rio Grande do Sul, Av. Bento Gonçalves 9500, Agronomia,91501-970, Porto Alegre, RS, Brazilc Instituto de Ciencias Exatas, Naturais e Educaç~ao (ICENE), UFTM, Av. Randolfo Borges Jr. 1700, Univerdecidade, 38064-200, Uberaba, Minas Gerais, Brazild Museo Municipal Argentino Urquiza, Jujuy y Chaco s/n, (Q8319BFA), Rinc�on de los Sauces, Neuqu�en, Argentina

a r t i c l e i n f o

Article history:Received 12 October 2014Accepted 19 February 2015Available online xxx

Keywords:TitanosauriaLithostratiaPeir�opolisPrefrontalSquamosal

* Corresponding author. Departamento de Paleontode Geociencias, Universidade Federal de Rio Grande9500, Agronomia, 91501-970, Porto Alegre, RS, Brazil

E-mail address: [email protected]

http://dx.doi.org/10.1016/j.jsames.2015.02.0090895-9811/© 2015 Elsevier Ltd. All rights reserved.

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a b s t r a c t

Isolated left prefrontal, left squamosal and atlas of titanosaur dinosaurs are described and compared.They come from the Late Cretaceous Serra da Galga Member of the Marília Formation at the Serra doVeadinho region, Peir�opolis (Uberaba County, Minas Gerais State, Brazil). Due to the sparse cranial ele-ments of titanosaurs already known from Brazil, these specimens are noticeable to be presented. Inaddition, the atlas vertebra is described for the first time for Brazilian titanosaurs. The morphology of thecranial bones closely resembles lithostratian titanosaurs, such as Rapetosaurus, rather than basal tita-nosaurs. The atlas is similar to that of other titanosaurs, suggesting that the anatomy of this elementseems to be more conservative than other vertebral elements, in which vertebral laminae play animportant rule in titanosaur taxonomy.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Titanosaur sauropods achieved a wide taxonomic diversitymainly in Gondwanan landmasses during the Late Cretaceous (e.g.,Powell, 2003; Wilson, 2006; Novas, 2009). The fossil record of thisgroup is particularly well-documented and studied in SouthAmerica, with about forty named species (e.g., Bonaparte, 1996;Powell, 2003; Novas, 2009). Remains of titanosaurs occur inalmost all Late Cretaceous faunal associations of South America,exhibiting a broad spatial as well as temporal distribution (e.g.,Bonaparte, 1996; Santucci and Bertini, 2001; Powell, 2003; Wilson,2006; Salgado and Bonaparte, 2007; Novas, 2009; Bittencourt andLanger, 2011). With regard to the Brazilian fossil record, titano-saurs are particularly notorious integrant of post-CenomanianCretaceous continental assemblages of southeastern Brazil (e.g.,

logia e Estratigrafia, Institutodo Sul, Av. Bento Gonçalves.(A.G. Martinelli).

i, A.G., et al., Cranial bones anState, Brazil, Journal of S

Kellner and Azevedo, 1999; Kellner and Campos, 2000; Santucciand Bertini, 2001, 2006; Kellner et al., 2005, 2006; Salgado andCarvalho, 2008; Bittencourt and Langer, 2011). The Bauru Group(Bauru Basin) includes the species Gondwanatitan faustoi (Ada-mantina Formation, S~ao Paulo; Kellner and Azevedo, 1999), Ada-mantisaurus mezzalirai (Adamantina Formation, S~ao Paulo; Santucciand Bertini, 2006), Aeolosaurus maximus (Adamantina Formation,S~ao Paulo; Santucci and Arruda-Campos, 2011), Brasilotitan nem-ophagus (Adamantina Formation, S~ao Paulo; Machado et al., 2013),Maxakalisaurus topai (Adamantina Formation, Minas Gerais;Kellner et al., 2006), Baurutitan britoi (Marília Formation, MinasGerais; Kellner et al., 2005), Trigonosaurus pricei (Marília Formation,Minas Gerais; Campos et al., 2005), and Uberabatitan ribeiroi(Marília Formation, Minas Gerais; Salgado and Carvalho, 2008).Outside this basin, Gondwanatitan sp. was also recognized in theCambambe Formation, Parecis Basin, in Mato Grosso State (Franco-Rosas et al., 2004) and Tapuiasaurus macedoi is known from theQuiric�o Formation, Sanfranciscana Basin, Minas Gerais State (Zaheret al., 2011). Beside the already described species, there is a hugefossil record based upon isolated remains that could be indicating anoticeably, still poorly known, higher diversity of titanosaurs (e.g.,

d atlas of titanosaurs (Dinosauria, Sauropoda) from Late Cretaceousouth American Earth Sciences (2015), http://dx.doi.org/10.1016/

A.G. Martinelli et al. / Journal of South American Earth Sciences xxx (2015) 1e72

Campos and Kellner, 1999; Kellner and Campos, 2000; Bertini et al.2001; Santucci and Bertini, 2001; Marinho and Candeiro, 2005;Lopes and Buchmann, 2008; Santucci, 2008; Bittencourt andLanger, 2011; Martinelli et al., 2011).

Of the aforementioned Brazilian species, cranial elements areonly known in Maxakalisaurus, Brasilotitan, and Tapuiasaurus. Theholotype of Maxakalisaurus includes a fragment of right maxillawith teeth (Kellner et al., 2006), whereas the holotype of Brasilo-titan includes a partial lower jaw with some teeth (Machado et al.,2013). Conversely, the holotype of Tapuiasaurus includes an almostcomplete skull and lower jaws, with teeth, which constitutes one ofthe most complete titanosaur skull ever found (Zaher et al., 2011);its full description will bring new information on cranial titanosaurmorphology.

In this note, two isolated cranial bones (Figs. 1e2) and an iso-lated atlas (Fig. 3) from Late Cretaceous Serra da Galga Member ofthe Marília Formation at the Serra do Veadinho region, Peir�opolis(Uberaba, Minas Gerais State, Brazil), are described. Due to thesparse cranial elements of titanosaurs already known from Brazil,these specimens are noticeable to be presented and compared. Inaddition, the atlas vertebra is described for the first time for Bra-zilian titanosaurs (the atlas of Tapuiasaurus is known but notdescribed yet; Zaher et al., 2011).

1.1. Institutional abreviations

CPPLIP, Centro de Pesquisas Paleontol�ogicas Llewellyn IvorPrice, Complexo Cultural e Científico de Peir�opolis/UFTM, Peir�op-olis, Uberaba, MG, Brazil.

Fig. 1. Isolated left prefrontal CPPLIP 1241 from the Late Cretaceous Marília Formation, site “

(Brazil) in lateral (A), medial (B), dorsal (C), and ventral (D) views. Abbreviations: b, orbital bo

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2. Geological settings

The sediments of the Bauru Basin were deposited in an inlanddepression formed by themomechanical subsidence related to theopening of the South Atlantic Ocean. It comprises roughly an area of370,000 km2, including portions of the Brazilian states of Goi�as,Mato Grosso, Mato Grosso do Sul, Minas Gerais (represented by theregion known as “Triangulo Mineiro”), Paran�a and S~ao Paulo(Fernandes and Coimbra, 1996). Bauru Basin is divided in twogroups: Caiu�a Group, with Goio Ere, Rio Paran�a and Santo Anast�acioformations, and Bauru Group, with Uberaba, Adamantina (¼Vale doRio do Peixe, Araçatuba, S~ao Jos�e do Rio Preto, Presidente Prudentesensu Fernandes, 2004) and Marília formations (Fernandes andCoimbra, 1996). The age of the rocks of the Bauru Group isconsidered by some authors as ranging from the Turonian toMaastrichtian (Dias-Brito et al., 2001), but contrarily Gobbo-Rodrigues et al. (1999) consider a shorter chronostratigraphicrange, suggesting it is Campanian-Maastrichtian based on the os-tracods of the Adamantina Formation of S~ao Paulo State. Magne-tostratigraphic studies by Tamrat et al. (2002) suggest that UberabaFormation could not be older than Campanian, strengthening thehypothesis by Gobbo-Rodrigues et al. (1999).

The specimens here studied come from the Serra do Veadinho,near Peir�opolis, from levels of the Serra da Galga Member of theMarília Formation. This member is a highly fossiliferous unit,composed of conglomerates and coarse-grained sandstones to fine-grained sandstones in fining-upwards cycles (Novas et al., 2008;Salgado and Carvalho, 2008). Within Serra do Veadinho region,CPPLIP 1241 (prefrontal bone) comes from the outcrop known as“Ponto 1 do Price” or “Caieira Site” whereas CPPLIP 296 (squamosal

Ponto 1 do Price” at Serra do Veadinho, Peir�opolis, Uberaba County, Minas Gerais Staterder; ffr, facet for the frontal; fn, facet for the nasal. Gray areas indicate broken surfaces.

d atlas of titanosaurs (Dinosauria, Sauropoda) from Late CretaceousSouth American Earth Sciences (2015), http://dx.doi.org/10.1016/

Fig. 2. Isolated left squamosal CPPLIP 296 from the Late Cretaceous Marília Formation, site “Ponto 2 do Price” at Serra do Veadinho, Peir�opolis, Uberaba County, Minas Gerais State(Brazil) in lateral (A), medial (B), anterior (C), and posterior (D) views. Abbreviations: bif, border of the infratemporal fenestra; bsf, border of the supratemporal fenestra; fpa, facetfor parietal; fpo, facet for postorbital; fpp, facet for the paroccipital process; fq, facet for quadrate; vp, ventral process. Gray areas indicate broken surfaces.

A.G. Martinelli et al. / Journal of South American Earth Sciences xxx (2015) 1e7 3

bone) and CPPLIP 247 (atlas vertebra) from the outcrop “Ponto 2 doPrice”.

Both sites present tabular geometry, planar cross-stratificationsand channel cross-stratifications (Novas et al., 2008). The fining-upwards cycles that occur on this outcrops are characterized byfine sandstones interbedded with pelites, clayish sandstones andcoarse sandstones with mud intraclasts (Novas et al., 2008). Thesefeatures suggest that these sediments were deposited by braidedfluvial systems that produced wide alluvial plains with small pondsand lakes in semi-arid to arid climate, and seasonality marked bylong dry periods intercalated with heavy rains and flash-floodevents (Garcia et al., 1999; Goldberg and Garcia, 2000; Novaset al., 2008). Despite the evidences of aridity, this paleoenviron-ment was humid enough to support water dependent organismssuch as fishes, anurans, turtles and semi-aquatic crocodyliforms,found as autochthonous or parauthochthonous remains.

3. Systematic paleontology

DINOSAURIA Owen, 1842

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SAURISCHIA Seeley, 1888SAUROPODA Marsh, 1878TITANOSAURIA Bonaparte and Coria, 1993LITHOSTROTIA Upchurch, Barrett, and Dodson, 2004Gen. et sp. indet.

3.1. Referred material

CPPLIP 247, isolated partial atlas vertebra (Fig. 3); CPPLIP 0296,isolated left squamosal (Fig. 2); CPPLIP 1241, isolated left prefrontal(Fig. 1).

3.2. Locality and horizon

CPPLIP 1241 comes from the site “Ponto 1 do Price” (19�4302400S,47�4404500W), at Serra do Veadinho, located approximately 2 kmnorth of the rural town of Peir�opolis, Uberaba County, Minas GeraisState, Brazil. CPPLIP 247 and CPPLIP 296 come from the site knownas “Ponto 2 do Price” (19�4301300S, 47�4500600W), at Serra do Vea-dinho, situated approximately 2.5 km north of Peir�opolis, Uberaba

d atlas of titanosaurs (Dinosauria, Sauropoda) from Late Cretaceousouth American Earth Sciences (2015), http://dx.doi.org/10.1016/

Fig. 3. Isolated partial atlas vertebra CPPLIP 247 from the Late Cretaceous Marília Formation, site “Ponto 2 do Price” at Serra do Veadinho, Peir�opolis, Uberaba County, Minas GeraisState (Brazil) in posterior (A), left lateral (B), anterior (C), and right lateral (D) views. Abbreviations: ic, intercentrum; np, neural spine.

A.G. Martinelli et al. / Journal of South American Earth Sciences xxx (2015) 1e74

County, Minas Gerais State, Brazil. All specimens come from Serrada Galga Member, Marília Formation (Campanian-Maastrichtian),Bauru Group.

4. Description and comparisons

4.1. Prefrontal

The prefrontal is a small bone which forms part of the dorsaledge of the orbit. CPPLIP 1241 consists of an almost complete leftprefrontal, lacking part of the anterior process (Fig. 1). It is a ratherstout bone, fairly rhomboidal (considering the broken anteriorprocess) in dorsal and ventral views and gently convex dorsally inlateral view, due to its correspondence with the dorsal orbital edge.This edge is rounded and, medially and anteriorly the prefrontalbecomes thicker. In the anterior portion of the orbital edge, thereare two small nutritious foramina and distally, there is a notch foranother foramen, which was enclosed between this bone and thefrontal. In dorsal view, the prefrontal is convex, with a smallnutritious foramen near the base of the anterior process (Fig.1). Thesurface of CPPLIP 1241 lacks ornamentation. In contrast, the ante-rodorsal margin of the orbit, on the prefrontal, of Nemegtosaurusmongoliensis (Wilson, 2005) is heavily ornamented by several smallpointed projections. Rapetosaurus krausei, also possess ornamen-tation, but much more subtle near its contact with the frontal(Wilson, 2005). The only partially visible facets in this view are forthe frontal and the nasal. These facets are better observed in medial

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and ventral views. The facet for the nasal occupies two-third of theprefrontal's antero-medial edge. It is almost vertical, relatively high,with small furrows, and encloses a ventrally opened vasculargroove, as in Rapetosaurus (Curry Rogers and Forster, 2004). On theother hand, the facet for the frontal is restricted to the one-thirddistal medial edge of the prefrontal in medial view, but with agreat development under this bone. As such, the prefrontal over-laps the frontal, leaving a large articular surface. Hence, in ventralview, the concave surface of the prefrontal has two main surfaces:the smooth roof of the orbital cavity and the rough articular facetfor the frontal (Fig. 1).

The anterior process of the prefrontal is broken off but based onits sub-triangular cross-section it should have been elongated andslender, as in titanosaurs (Rapetosaurus, Tapuiasaurus; Curry Rogersand Forster, 2004; Zaher et al., 2011), for contact to the lacrimal.Contrarily, in Nemegtosaurus the anterior process is reduced(Wilson, 2005) and in basal macronarians, such as Camarasaurus(Madsen et al., 1995), this process is absent. Although the generalshape of this bone is similar to that of Rapetosaurus, the articularfacet for the frontal is better developed than in the African speciesand the posterior end is not transversely straight.

4.2. Squamosal

The isolated squamosal CPPLIP 296 corresponds to the left sideof the skull. It is an L-shaped bone in lateral view, with a main bodyand a cranio-ventrally descending process (Fig. 2). This element has

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A.G. Martinelli et al. / Journal of South American Earth Sciences xxx (2015) 1e7 5

several articular facets to accommodate others cranial bones (i.e.,postorbital, parietal, exoccipital þ opisthotic, and quadrate). Thebody of the squamosal has a lateral, vertical and almost flat surface,with a laminar descending process (or ventral process), and adorsal, slightly convex surface, which participates of the skull roof.In lateral view, the squamosal bears a well-delimited, deeplyconcave scar for contact with the postorbital (Fig. 2). This concavityfaces latero-anteriorly and its ventral edge coincides with thebeginning of the postero-dorsal border of the infratemporalfenestra (Fig. 2). The descending process is thin, long, slender andD-shape in cross-section with the outer surface slightly convex andthe inner surface slightly convex to straight. The ventral andantero-ventral edges of this process are broken off. As preserved, itseems that anterior and posterior borders are sub-parallel butpossibly the anterior edge slightly diverges ventrally. The anterioredge of the descending process delimits the posterior border of theinfratemporal fenestra. On the other hand, its posterior edge con-tacts the quadrate through an articular surface which extends ontomost of the inner surface (Fig. 2).

In posterior view, the main features are the concave articularfacet for the paroccipital process of the opisthotic and the innerarticular facet for the quadrate (Fig. 2). The scar of the paroccipitalprocess is postero-medially projected and not visible in lateralview. In medial view, the facet for the parietal is oval shaped, with arugose texture, located in the dorsal-most portion of the squamosalbody. Next to this facet, there is a small portion of the posterioredge of the supratemporal fenestra. The articular facet for thequadrates is best seen in medial view; it has some shallow, sub-parallel dorso-ventrally oriented ridges (Fig. 2). This facet is ante-riorly delimited by a medial process that becomes taller upward.

The long and slender descending process of the squamosal issimilar to that of Rapetosaurus (Curry Rogers and Forster, 2001,2004) and Nemegtosaurus (Wilson, 2005) and rather different tothat of Tapuiasaurus, which has a more robust and dorsoventrallyshorter process (Zaher et al., 2011), and Phuwiangosaurus sir-indhornae, in which it is very short and hook-shaped (Suteethornet al., 2009). In CPPLIP 296 there is clear evidence that the squa-mosal participates of the posterior edge of the supratemporalfenestra as in Rapetosaurus (Curry Rogers and Forster, 2004),differing from Nemegtosaurus and Quaesitosaurus orientalisKurzanov and Bannikov, 1983, in which this bone is excluded fromthis fenestra (Nowinski, 1971; Upchurch, 1995; Wilson, 2005). InQuaesitosaurus the squamosal is a massive and elongated bone,with dorsal and posterior surface intensely roughened (Kurzanovand Bannikov, 1983), differing from the smooth surface of CPPLIP296.

The taxonomic referral of the squamosal to Titanosauria indet. issupported by its resemblance to the squamosal of the derivedlithostrotian Rapetosaurus, from the Late Cretaceous of Madagascar(Curry Rogers and Forster, 2001, 2004). Although the specimenCPPLIP 296 cannot be referred to any particular taxon, itsmorphology is reminiscent of lithostratian titanosaur rather than tobasal forms. For example, in more basal taxa, such as the basalmacronarian Camarasaurus sp. (Madsen et al., 1995) and non-titanosaur titanosauriform Abydosaurus mcintoshi (Chure et al.,2010), the squamosal is a stout element, quite different from themorphology of CPPLIP 296. Also, this element is quite different fromthe squamosal of the diplodocid Diplodocus, in which there is aprominent medial process (e.g., Yu, 1993) not observed in CPPLIP296 and other titanosaurs (Curry Rogers and Forster, 2004).

4.3. Atlas vertebra

CPPLIP 247 consists of an almost complete atlas (Fig. 3). Thefusion of the neurapophyses to the intercentrum indicates that the

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specimen belongs to an adult individual. The atlantal intercentrumis robust, much wider transversely than it is high, such as Mon-golosaurus (Mannion, 2010) and Futalongkosaurus (Calvo et al.,2007). The anterior face of the intercentrum, for the occipitalcondyle, is concave and the posterior one is flat, such as in othertitanosaurian atlas. The lateral surface of the intercentrum is mildlyantero-posteriorly concave, such as in Quetecsaurus rusconii(Gonz�alez Riga and Ortiz David, 2014), Mongolosaurus, and Rape-tosaurus (Curry Rogers, 2009). Similar to Rapetosaurus and Futa-lognkosaurus, CPPLIP 247 lacks the two well-developedposteroventral processes which are present in Quetecsaurus andvery reduced in Erketu ellisoni. The neurapophysis is proximallyhigher than in Mongolosaurus, Rapetosaurus, Futalongkosaurus, andErketu ellisoni (Ksepka and Norell, 2006). The upper parts of theneurapophyses are thin, and posterodorsally projected, but do notapproach one another on the midline, similar to Mongolosaurus,Futalongkosaurus and Rapetosaurus. In CPPLIP 247, the parts of theneurapophyses are more separated medially that other titanosauratlas. The atlas of Erketu shows the neurapophyses fused at themidline. The neurapophyses in CPPLIP 247 are posterodorsallyprojected in an angle of 45� similar to Mongolosaurus. In Futa-longkosaurus the angle is about 50� while in Rapetosaurus andErketu, between 30� and 40�.

5. Discussion and conclusion

The titanosaur context at the paleontological quarries locatedalong the Serra do Veadinho, near Peir�opolis town (Uberaba, MinasGerais State, Brazil), is quite diverse including the titanosaursTrigonosaurus pricei (Campos et al., 2005; Ju�arez Valieri and Díaz,2013) and Baurutitan britoi (Kellner et al., 2005). In addition,there is an isolate caudal vertebra of an Aeolosaurini indet.(Santucci and Bertini, 2001; Martinelli et al., 2011; Filippi et al.,2013) and several specimens of indeterminate titanosaurs (e.g.,Campos and Kellner, 1999; Santucci and Bertini, 2001; Marinho andCandeiro, 2005). The specimens here described constitute the firstcranial bones of titanosaurs from this region and unfortunatelycannot be referred to any particular taxon rather than indetermi-nate lithostrotian titanosaurs. The skull anatomy of titanosaurs islargely based upon only a few, almost complete, skulls (e.g., Nem-egtosaurus, Rapetosaurus, Tapuiasaurus; Nowinski, 1971; CurryRogers and Forster, 2001, 2004; Wilson, 2005; Zaher et al., 2011)and isolated and/or non-articulated remains (such as, mandibles,braincases, isolated bones) (e.g., Powell, 2003; Apesteguía, 2004;Martinelli and Forasiepi, 2004; Kellner et al., 2006; García et al.,2008; Filippi and Garrido, 2008; Filippi et al., 2011; Gallina andApesteguía, 2011; Machado et al., 2013; Curry Rogers and Wilson,2014), which in comparison with the total number of recognizedspecies, this information is still quite limited.

The prefrontal and squamosal have some features that arereminiscent of derived lithostratian titanosaurs, such as Rapeto-saurus from Madagascar and Tapuiasaurus from Brazil. The squa-mosal CPPLIP 296 has a long and slender descending process as inRapetosaurus (Curry Rogers and Forster, 2001, 2004) and Nem-egtosaurus (Wilson, 2005). Contrarily, this process is more robustand dorsoventrally shorter in Tapuiasaurus (Zaher et al., 2011). Ac-cording to the phylogenetic hypothesis of Zaher et al. (2011),Nemegtosaurus is the sister taxon of theRapetosaurus þ Tapuiasaurus clade, all constituting a monophyleticNemegtosauridae. Therefore, two configurations of the descendingprocess of the squamosal are recognized into this family. As a result,the specimen from Peir�opolis has a character-state similar to thenon-South American Rapetosaurus and Nemegtosaurus rather thanto Tapuiasaurus from Brazil. Because the distribution of this char-acter among others non-nemegtosaurid “advance titanosaurs” is

d atlas of titanosaurs (Dinosauria, Sauropoda) from Late Cretaceousouth American Earth Sciences (2015), http://dx.doi.org/10.1016/

A.G. Martinelli et al. / Journal of South American Earth Sciences xxx (2015) 1e76

still poorly known, we could not conclude with confidence that thesquamosal CPPLIP 296 belongs to nemegtosaurid. At present, it ismore parsimonious to consider CPPLIP 296 as a derived lithos-tratian titanosaur, with close resemblance with some nem-egtosaurids. Nonetheless, CPPLIP 296 is clearly differentiated fromthe squamosal of Tapuiasaurus, indicating it belongs to a differenttaxon.

With regard to the prefrontal, CPPLIP 1241 is more similar tothat of Rapetosaurus and Tapuiasaurus (Curry Rogers and Forster,2004; Zaher et al., 2011) than to that of Nemegtosaurus (Wilson,2005). Because the configuration of this bone among titanosaursis also poorly known, CPPLIP 1241 could only be referred as alithostratian titanosaur (see comparisons in the description).

Although based on sparse data, the prefrontal and squamosalhere described are indicative that the titanosaurs from Peir�opolisregion had a skull configuration similar to nemegtosaurids, such asRapetosaurus. Also, the difference in size between the squamosal(smaller) and the prefrontal (larger) indicates different ontogeneticstages or two different taxa with different skull sizes. Only morecomplete and associated specimens will permit to elucidate theseproblems.

The atlas, although incomplete, has a similar pattern that ofother titanosaurs, such as Futalongkosaurus (Calvo et al., 2007),Rapetosaurus (Curry Rogers, 2009), and Mongolosaurus (Mannion,2010). Therefore, the anatomy of this element seems to be moreconservative than other vertebral elements, in which vertebrallaminae play an important rule for titanosaur taxonomy (e.g.,Bonaparte, 1999; Wilson, 2012).

Acknowledgments

We thank the continuous support of all the staff of the ComplexoCultural e Cientifico de Peir�opolis (CCCP) of the Universidade Fed-eral do Triangulo Mineiro (UFTM), Uberaba, MG, Brazil. Thiscontribution was beneficiated by the financial support of theFundaç~ao de Amparo �a Pesquisa do Estado de Minas Gerais(FAPEMIG), the Conselho Nacional de Desenvolvimento Científico eTecnol�ogico (CNPq), the Coordenaç~ao de Aperfeiçoamento de Pes-soal de Nível Superior (CAPES), the Fundaç~ao de Ensino e Pesquisade Uberaba (FUNEPU) and the Minist�erio de Ciencia Tecnologia eInovaç~ao (MCTI). The reviewers M. Ezcurra, F. Agnolin and the theEditor J. N. Kellogg and C. R. Candeiro provided useful commentsthat greatly improved the Ms.

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