Late Cretaceous vertebrates from Bajo de Santa Rosa ( Alien Formation ) , Rio Negro province , Argentina , with the description of a new sauropod dinosaur ( ' ll ' itanosauridae )

titanosaurid dinosaurs. A now small salt,asaurine tit&saurid, I3onatitan reigigen. el sp. no"., is described. I t is diagnosed by the following association of characters: 1) longitudinal groovo located an the suture between pariotals that continues posteriorly over the supraoccipital to the foramen magnum; 2) basisphcnoid tubera long and narrow; 3) dorsalto middle caudal vertebrae with deep oval to circular pits present on both sides of the prespinal lamina; 4) anterior caudal vertebra with spino-postzygapophysiat and spino-prezygapophysiai laminae; 5) neural arch of anterior caudals with deep interzygapophysial fossae with numerous pits; 6 ) anterior caudal vertebra with an accessom sub-horizontal lamina extendine from the antero-ventral oortion of the " postzygapophysis to the mid-portion of tho spino-prezygapophysial lamina; and finally, 7) anterior caudal vertobra with a prominent axial crest on the ventral surftaee of tho cerntrum. The first rocord of sphenodonts and cf carcharodontosaurid theropods is recognized for the upper Late Cretaceous ofpatagonia, as well as the earliest record of perichthylds (Pereiformes). The vertebrate record is mainly composed of terrestrial and freshwater tawa, but a few marine elements are found (olasmosaurids) indicating a marine influence during the deposition of the Allen hrmation in the arca of Baio de Santa Rosa. The vertebrate remains s u ~ ~ o r t a Cam~anian-


LOCATION AND GEOLOGICAL SETTING
The Bajo de Santa Rosa locality is 1ocal.edapproximately 150 km south west from ttie city of lamarque, approximately in the so~ithern center of the Rio Negro Province (Fig, 1).In this area, the exposed Mesozoic sedimentary rocks correspond to three Late Cretaceous formations: Bajo de la Carpa, Allen, and Jagiiel (Hugo & Lcanza, 2001).The Bajo de la Carpa Forrnation belongs to the Rio Colorado Subgroup from the Neuqu4n Group (Hugo & Leanza, 2001) and its age is presumed t o b e Coniacian-Santoniari (Legarreta & Gulisai~o, 1989;Bonaparte, 1991).The Allen and Jagiiel Sormations that correspond to the M a l a r a e Group overlie discordantly the Bajo de la Carpa Forrnation.According to recent studies (Hugo & Leanza, 2001) both the Bajo de Pa Carpa and Jaguel formations are poorly represented a t the Uajo de Santa Rosa locality; contrary, the Allen Formation shows widely exposed outcrops (Fig. IB).
The formations that comprise the Malargue Group ( l a t e Camparlian-Early Paleocene sensu Legarreta & Gulisano, 1989) vary according to their position in the Neuquen basin.In the southeast of the hasin the sedimentary sequence comprises (from Llie base to the top respectively) tile Allen, Jagiiel, Roca, and El Carrizo formations.In the northwest of the basin the Malargze Group is formed by the following units: I,oncoche, Jagiiel, Roca, and Pircaia Sormations (c.g., Barrio, 1990).
The Jagiiel Formation overlies the Allcri Formation in t,he area oS Bajo de Santa Rosa.The age inferred for the Jaguel Formation is Late Maastriclitian-Early Danian (e.g., Casadio, 1994); the Crctaceous-Pilleocene transition (I<-Ti was recognized in the upper part of the sequence (Coiichcyro et al., 2002).
The Allen Formation at Bajo de Santa Rosa consists of two rnemhers each about 70 meters thick (Hugo 85 I,eanza, 2001).The lower member is composed of alternated sandstones arid mudstones with small lents of conglomerates.The upper rneniber is dominated by gray pelites covered by limestone and gypsum (Page et al., 1999;Hugo & Leanza, 2001.).
All tho specimens described here (Table 1) wore collected in the lower member of the Allen Formatiori exposed at Bajo de Sarita Rosa (Fig. 1).
Up to now, the only Ljrnilies recognized in the Cretaceous of S o u t h America a r e the Diplomystidae, Ariidae, Andinichthyidae, and possible Doradidae, but due to the Sragrnerittary nature of most of the specimens referred to tlicse families, further studies and inaterials are required to confirm these interpretations (Arratia & Cione, 1996;Cione & Prasad, 2002).
Deswiplio~~.Dospite their Eragmeiitary inature, tlnese remains show differences with the catfish (Diplornystidae) reinains cornrneinted above.The speciirien MACN-PV RN 1084 represents the largest siluriform Rom Bajo de Santa Rosa (Fig. 2B).Tlie spine is slightly curved, lacks aiiterior deiiticles, wit11 the small postcrior ones articular facet located in a longitudinal groove.The spine is almost circular in cross-section and the dorsal and ventral surfaces are covered with shallow loogi., tudinal furrows.
In the Cour specimens catalogued as MACN-PV RN 1074, the proximal portion of the spine 1s missing.The denticles are located only on one edge (possibly the posterior margin); they are sharp, inclined, and a s long as the spine width (Fig. 2C).A similar type of pectoral spine has been also discovered in the siluriforms from the Los Alamitos Formation (Cione, 1987: Fig 1B).
At the moment, these fossil remains are referred to Siluriformes incertae sedis.At least three different morphologies were identified that could be related to different siiuriform taxa.
Description.At least six incomplete vertebrae were found a t Bajo de Santa Rosa.The vertebral apophyses have not been preserved in most specimens.All the vertebrae show the diagnostic feature of Lepisosteidae in having an opisthocoelous centrum (Cione, 1987).
T(?leostei Miiller, 1844 incertae sedis (Fig. 2E) Referred Material.MACN-PV RN 1077: tcn hemispherical teeth of different sizes.ered it to be Teleostei incertae sedis (Cione, personal communication in GonzBiez Riga, 1999)  Description.One of these remains corresponds to ail anteriormost vertebra due to the presence oi' the a r t i c u l a r surface for t h e exoccipital (only preserving the right one), which kces antero-dorsally (following Arratia, 1982) The neural arch and spine are autog(+nous.The postzygapophyses are broken offand behind this region there is a large circular depression possibly for rib articulation (Gayet, 1987; Fig. 2F).Thc anterior surface ofthe centrum is larger than the posterior one.In all ccntra (Figs.2F, G), there are numerous deep cavities of different shapes and sizes on the lateral and ventral surfaces, separated by bony trabeculae (Figs.2F, Gj.The vertebral centra range frorri 2 to 9 millimeters in diameter. Comments.The autogenous neural arch is a characteristic feature of the Perciformes (Gayet, 1987).The pattern of ornamentation with deep cavities in the vertebral centra is common in two families of Perciformes: Ccntropomidae and Percichithyidae (e.g., Arratia, 1982; Gayet, 1987,  1991 1.The Centropomidae are tentatively recognized in the Paleocene of Tiupampa (Bolivia) (Mi~izon et al., 1983;Gayct, 1991;Arratia & Cione, 19961, while the Percichthyidae are known Srom the Maastrickitian of Bolivia (Gayet & Mcunier, 1998;Gayet et al., 2001 ), the Eocene and Miocene of Argentina and Chile (Schaeffer, 1947;Arratia & Cione, 1996), and Oligocene-Miocene of Brazil (Arratia, 1982).Rornains tentatively rererred to Centropomidae or Percich-thyidae were also reported from the Marilia Formation (Bertini et al.,19Y3), but further studies must be performed to clarify their taxonomic status.The living Ereshwater Percichthyidae are represented by six species belonging to the genus Percichthys that inhabit the southern and western regions of Argen-lJ,,, ,,.,,,!j ,u.&om 6 to 15 millimeters.Santa Rosa to the basal family of percoids Comments.Similar teeth, although smaller, Percichthyidae because they share a similar verhave also been found in Los Alamitos and tebral morphology with those Percichthyidae Loncoche formations (Cione, 1987; GonzBlez such as Macquaria antiquus (Gayet, 1987) andRiga, 1999).This kind of tooth was originally the living Percichthys trlicha (Arratia, 1982 181, assigned t o Semionitidae (?Lepidotes sp.) or especially in the morpholo&y ofthe anteriormost Sparidae (Cione, 1987) but later studies consid-vertebra.Thesevertehralremains from the Allen Formation possitbly rt?present the earliest record oS Pcrcichtliyidae in t h e Canipanian-Maasi.rich1ian of South America.However, a widerange of comparison among other basal families orpcrcoids rnust be done Lo clarify the taxononiy of these remains.
Deacriution.iLlilCN-PV RN 1079 sneci~nen has four ridges (Fig. 21).The first ridge is the largest, and the others decrease in size toward the medial edge (fi,llowing Llie ter~riiriolo&y of Martin et a/., 1999); tlic secorid ridge is broken.The first cn:st is tall and sharp.The lingual and mesial edges are sligiitly convex, almost similar in length.The occliisal s ~i r h c e is covered with small pits of regular size.MACN-PVRN 1079 resembles the specimens of ~d!errrtodusx from the Bajo de Santa Rosa and otlier localities figured hy Wichmann (1927: Piate I), tlic specimen of .<Ceratodus-iheringifrom tho Los Alamitos Formatior?figured by Cione (1987), and one specimen of *eCeroioduss.sp, from the Coii Toro Formation figured by Pascual and Boridesio (1976: Plate 1.5).
Description.Many isolated amphicoelok~s celltra of chondrichthycs have been found (Fig. 2J); these range in diamet,er from 6 to 16 mm.The neural and hemal processes are not preserved.
Cormnents.Similar vertehrae were described fkom the 1,os Alamitos Formation (Cione, 1987) and referred to Ratoidea, based on studies and comparisons of thin sections of these hones.In addition, many isolated teeth of Batoidea also were found in Los Alamitos locality (personal observation) that is conguenl with the previous assignation.Due to the lack of preparation of thin scctioiis on the vertebrae horn Bajo de Sarila Rosa, as well as the prescrvatiou of any other fossil elements that could help in the family identilication we tentatively consider these remains as Chondrichthyes iilcertae sedis.

ANURANS
In the Cretaceous of South America, anurans are represented by at least two dist~nctive groups, the ancient Pipoidea and the neohatrachian Leptodactylidae.
The Leptodactylidae are a paraphyletic assemblage of neobatrachian frogs (we use this familiar name until a revision of the taxonomy of the group is undertaken) that inhabit terrestrial or aquatic environments (e.g., Lynch, 1971;Duellman & Trneb, 1986;Ford & Cannatella, 1993).They are recorded in the Los Alamitos (represented by an unnamed taxon closely related t o the living teimatobine Caudiuerbera; Biez, 1987) and possibly Loncoche formations (Gonziiez Riga, 1999) of Argentina; and in the Marllia Formation o? Brazil (the ceratophryne Baurubatrachus pricei; BBez & Perf, 1989).The Leptodactylidae were divarse and are relatively well documented in the Paleogene and Neogene fossil record of South America (e.g., Schaeffer, 1949;Casamiyuela, 1958;Sigi., 1968;Baez, 1977Baez, , 1991Baez, , 1996;;Bonaparte et al., 1993).Description.The sphenethmoids probably correspond to the same species based on the shared morphology and the approximate similar size.The sphenethmoids are arrow-shaped, dorso-ventrally flat, with two large external narial openings (Figs 3A, B).The orhitonasal foramina are located at the anterior hail of the sphenethmoid, below a distinctive dorso-lateral shelf.The frontoparietal fenestra opens in dorsal view; it is wider than in the Paleocene pipid Shelania (BBez & Trueb, 1997).The frontoparietal fenestra is anteriorly surrounded by the sphenethmoid, a piesiomorphic trait also present in non-xenopodines and nonpipine pipids (Biez & Pugener, 2003).The nasal septum is visihle on the anterior margin of the fenestra.In ventral view, a small fragment of the parasphenoid with the anterior end broken off is observable in MACN-W RN 1065 (Fig. 3B); the specimen MACN-PV 1064 has a shallow depression that extends anteriorly for the support of the cultriform process of the parasphenoid (Fig. 3A).In both specimens, the anterior border of this depression is not clear; and a surface for the vomer is not observed.The optic foramen is only preserved on the left side in MACN-PV RN 1064 and is fully enclosed by the sphenethmoid.
Com,ments.The optic foramen enclosed by the sphenethmoid supports the familiar assignation because it is considered a synapomorphy of the Pipidae (Cannatella & Trueb 1988;Bhez & Trueb, 1997;Baez & PCgener, 19981, and for that reason both specimens are assigned to this family The absence of the vomer could also support pipine affinities k g ., BBez & PCgener, 19981, hut as ihe specimens ofBajo de Santa Rosa are poorly preserved, we prefer to avoid this feature in our identification.
Description.The fragment of the right maxilla and the remaining cranial bones are assigned to this family due to the strongly ornamented external surfaces.The exostosed cranial ror~f bones are covered with deep subcircular pits o? diverse size (Figs 3C, D); the ornamentation in tho maxilla decreases near the alveolar border.This type of ornameiltation is widely reported in fossil Leptodactylidae such as Baurubatrachus proximal region of the shaft.The distal end is pricei (Bbez & Peri, 1989) and Caudiuerbera wide and the epiphysis is rnainly ossified on the casamayorensi,~ (Schaeffer, 1949;Baez, 1977).On radius.The vertebral remains consist of poorly the rnedial aspect of the maxilla, there are high preserved bodies andfrabmentary neural arches, and narrow alveoli; the teeth were not preserved therefore they are not fippred neither compared.(Fig. 3C).The assignation is based upon compari-Comments.No autapomorptiies for family sori with tine material described from tile Los determination couldhe recoimizedin these snrci-Alamitos Formation (BBez, 19871, Baurubat l ~~c h ~s p r i c e i (BBez & Peri, 19891, and Ceriozoic leptodactylids (e.g., Schaeffer, 1949;BBez, 1977;Casamiquela, 1958), which have the same type of ornamentation.
The right humerus (Fig. 3E) is lacking the proximal end, and most ofthe deltopectoral crest has been broken off.The shaft is transversely narrow and dorso-ventrally wide.The medial and lateral edges diverge distally.The eminentia capitata is prominent, simiiar to that seen in the Los Alainitos leptodactylids (BBez, 1987), but less developed t h a n in t h e known Paleocene leptodactylids (i.e., taxa from .<BancoNegro Inferior. of the Salamanca Formation, Punta Peligro, Chnbnt, Bonaparte et al., 1993;andEstesiella boliuiensis from Bolivia, Baea, 1991, 1995).The medial epicondyie is more prominent than the lateral one, ventrally projected as a blunt crest, and with a dist,al notch that separates the epicondyle from the eminentia capitata.Similar features are present in Est,esiella (BBez, 1991(BBez, , 1995) ) and the Punta Peligro leptodactylids (Bonaparte et al., 1993) 3F); MACN-PV RN 1070: fused radio and ulna (Fig. 3G).
Description.The specimen figured (MACN-PV RN 1066; Fig. 3F) corresponds to a right angulosplenial of medium size.The coronoid process is mediaily projected and has a semicircular shape.The groove for the dentary is deep, faces ventro-laterally, and extends posteriorly to the coronoid process.The area for articulation with tile skull is not preserved in any of these hones.
The left fused radius and ulna (Fig. 3G) has a prominent olecranon process and a neck in the The Cryptodira is a very large group of fossil and extant turtles widespread around the world.Among them, l i ~e Meiolaiiidac is the ocly group recovered in the Cretaceous of South America.The Meioianidae are n~edium to large bodied-sized fully terrestrials turtles.This family tias heavy shells, a tail club, frills, and cranial horns (e. g., Ameghino, 1899;GafSney, 1983GafSney, , 1996)).Meiolanid turtles were lbund in the Late Cretaceous Los Alamitos (Broin, 1987) and La Colonia (Gasparirii & de la Fuente, 2000) formations.
Isolated remains of turtles from Bajo dc Santa Rosa were first figured by Whichmann (1927); here we report many isolated and frag- mentary shells and postcranial remains collected in the same locality.The ornamentatiou of the shells is very similar to that reported in other Chelidae (e.g., Broin, 1987;Gasparini & de la Fuente, 2000).Fragments of xiphiplastrons show the suture for the pelvis as it occurs in all Pleurodires (e.g., Rroin, 1987; Lapparent de Broin & de la Fuente, 2001).The available specimens are extremely fragineritary and do not allow the recognition of tile synapomorphies of the cllelids; however, at least three different types of caparaces @en.et sp, iitdet.1,2, and 3 ) have been recognized on the basis of their size arid external ornamentation.Betier-preserved turtle specimens from the Allen Formation are currently under study (de la Fuente, personal communicaiion).Desci-iption.These specimens correspond to the largest unnamed turtle from the Bajo deSantdRosa locality (Fig. 44.).The ornamentation is slight, with irregular polygons and dichotomized furrows.
Ilescription.These specinlens correspond to a small to xncdium sized turtle with a heavy ornamented carapace (Figs.4B, C).The plates are thick and hear deep irregular elongated polygons on t h e external surface.The fragment of xiphiplastron shows the suture for the pelvis (Fig. 4B), which is considered an autapornorphy of pleurodires (e.g., Broin, 1987; Lapparent de Broin 8: de la Fuente, 2001).
Description.The rriaterials belong to the srnallest turtle specirneri collected a t Bajo de S a n t a Rosa.T h e plates a r e t h i n a n d lack macroornamentation (Fig. 4D).
Conaments.This type of shell was reported in the Los Alamitos (Broin, 1987) and La Colonia (Gasparini & de la Fuente, 2000) Cormations.This specimen could be tentaliveily referred to the Phr-yr~ops group; the size and the external surface of t h e shells resemble Bonaparle~nys bajobarrealis (from the Turonian-Campariiari Rajo Barreal Formation) and Palaeophrynops iencias rVc~lurales, n. s. ( ; 121, 2004 patagonicus (from the Los Alamitos Formatiori; Lapparerit de Broin 8: de la Fucnte, 2001).Nevertheless, based on the fragmentary nature o f t l ~e specimens we tentatively corisider them as Chelidae indet.
Description.All the collected specimens are isolated elements; the size varies among them suggesting that these elements correspond to different individuals.The cervical centra have facets for the articulation of tine single-hoaded ribs; they are latero-ventrally orierited (Fig. 4E) rather than laterally oriented as seen in the dorsal and caudal vertebrae.The centruni is dorsoventrally low, antero-posteriorly short, trarisverseiy wide, and slightly arnphicoelous.Both anterior and posterior art~cular surfaces are kidney-shaped On the ventral surPace twu large foramina are present.
(Fig. 4F)  cates the presence of sphenodonts in the Allen Formation a t Bajo de Santa Rosa.The dentary (Fig. 4F) is high and hears a longitudinal depression on its labial surface.The teeth are fully acrodont with flanges (synapomorphic features shared by this specimen and the crown-group sphenodonts; Sues et al., 1994).The teeth are lingually placed and slightly transversely flattened with the main axis mesiolingual-distoiabiaily oriented.The distal edge imbricates slightly labially towards the posterior tooth, as in other sphenodonts (e.g., TingLiana anouolae from the Early Cretaceous of Morocco; Elrans & Sigogneau-Russel, 19971.The posterior teeth are larger than the anterior ones.Wear facets are present on the tip of the two tallest teeth.The presence of well established wear facets on the teeth is a feature share with Sphenodontidae (e. g., Reynoso, 2000).
Comments.This specimen represents the first record of Campanian-Maastridltian sphenodonts in South America, and possibly indicates the persistence of a gondwanan lineage of Cleuosauruslike sphenodonts yet poorly known in the Jurassic and Cretaceous beds of South America. Kaikaifilasaurus caluoi (Sim6n & Kellner, 2003) and Priosphenodon auelasi (Apesteguia & Novas 2003; probahlj~ ajunior synonymous ofK.caluoi) both from t,he Cenomanian Candeleros Formation (Neuquen and Rio Negro) a r e Eilenodontinae sphenodonts; they are characterized by the presence of a deep dentary and transversely wide teeth (Sim6n & Keliner, 2003;Apestcguia & Novas, 2003), features clearly different from the specimen from Bajo de Santa Rosa.
Herein, we comment t h e presence of Alamitophis argentinus Alhino, Patagoniophis pamus Albino, undetermined madtsoiid remains, and a medinm-siae ?madtsoiid trunk vertebra, which in our view belongs to a new taxon.In addition, preparation and observation of a new trunk vertebra of Rionegrophis madtsoioides Albino from Los Alamitos s u p p o r t s i t s Madtsoiidae affinities, as was initially interpreted (Alhino, 1986).
Comments.Up to now, this smallest species of madtsoiid was recognized in the Los Alamitos Formation (Albino, 1986,19871, and  Description.Only a n incomplete vertebra could be assigned tentatively to A. argenlinus (Fig. 5B1.This specimen bas only the centrnm and part of the left portion of thc neural arch preserved.The specimen li.om Bajo de SantaRosa shares with the holotype of A. argenlinus (Halotype MACN-PV RN 27; Albino, 1986) a similar morphology of the vertebral centrum, including a narrow and not very triangular in shape, with a thick haemal keel separating deep lateral depressions.This material is slightly smaller than the holotype ofii.argentinus (MACN-PVKN 33).
Comments.Alnrnitophis (Albino, 1986) is widely documented in the Los Alamitos, Allen, and La Colonia formations, as well as in the Early Eocene ofAustralia (Albino, 1994(Albino, ,2000;;Scanlon, 1993).If the taxonomic identifications of these records (only based on vertebral isolated remains) are correct, this species has a broad temporal and geographic distribution in Gondwana.
As a preliniinar c ~~m m c n t , Alamitophis seems lo be the predominat snake in the Los Alamitos, Allen, and La Colonia forrnations.
Madtsoiidae Hof 'fstettcr, 1961 Cen. et  Ilescription.MACN-PV RN 1052 (Fig, 5C) is the must complete vertebra Srom Bajo de Santa Rosa that is referred to this l'dmily This veriehra has a parazygantral foramen wtiich is a unique vertebral synapomorphy of Madtsoiidae (Rage, 1998).This specimen is a little larger than Patngoniophis par-ous a n d smaller tliari Alainitophis argentinus.The vertebra is high arid short.The haemal keel it* thin and limited laterally by deep depressions.'The neural spine is broken off on its posterior part.The zygailtrum is high and deep with the dorsal border slightly concave.The association of t,hese mentioned Seaiures in the vertebra from Bajo de Santa Rosa differs significantly from i'atagoniophis and Alamitophis making it difficult iu assibm it t o genus level.
M-4CN-PV RN 1051 (noi figured) corresponds to a caudal vertebra due to the presence ofa pair of pcdiceis for ttie cl~evrons near the posterior end of the centrum, arid long narrow transverse processes ar~toro-laterally projected.
Cornmetits.The specimen here described represents the largest snake recovered From the Bajo de Santn Rosa locality The familiar status of this taxon is doubtful due t o the lack of the postzygapophyses and part ofthe xygantrurn where the parazygantral foramen should be located.The combirialion of these features mentioned in this specimen could indicate the presence of a new taxon, hut new findirigs are required iii order to support this statement.In addition to this speciinen, uripublished vertebrae fmrn the 1,os Akamitos Formation could be assigned to the same taxon.Ruferred Mc~tei-id.MACN-PV RN 1059: al-Thesesueciniens are: W C N -P V RN 201.MACK niost complete trunk vertebra.
Description.MACN-PV RN 1059 (Fig. 6) coilsists of a t r u n k vertebra lacking both postzygapopliyses, the anteriormost part of the prezygapophyses, and the postero-dorsal portion of the neural spine.Ttie vertebra is lligl~ and wide.The dorsal edge of the neural spine, alt.hongl, incomplete, seems to be straight.The zygosphene is weak, trarisvcrscly elongate, and low.The prezyg.apophyses are ant,ero-laterally projected and PV RN 519, and MACN-PV RN 220.
Commenls of lZioiiegraphis ~nadtsoioides.An undescribed trunk vertebra (MACN-PV RN %261 of Rionegrophis n~adtsoioides from t h e Los Alainitos Formation provides new information about the taxonomic affinities of this species.N- bino (1986, 1987) tentatively included this taxon in the Madlsoiinae subfirriiiy b<!cause one diagnostic feature (i.e., the presence of a parazygantral foramen) was not preserved in tile holotype and the apparently do not have aprezygapophyseal process only available specimen.MACN-PV RN 226 shares on tlie riclit side where the nreavmnool~vsis is hetwith tllc holotvoe of Rione~roohis madtsoioides .,A " L " .
In recent ycnrs, the phylogenctic relationships ortitanosaurian sauropods have been reviewed by different authors, and the general consensus is that the titanosanrid Saltasaurinae appaars to be one of the most derived groups from this lineage (e. g., Salgadoet al., 1997a;Upchurch, 1995Upchurch, ,1998;;Wilson, 2002).
A new small saltasaurine titanosaurid, Donatitan reigi gen.et sp.noo., based or1 two incomplete specimens is described and compared here.These two specinlens were unearthed together from the same site at the Bajo de Santa Rosa locality Diagnosis.Small-sized titanosaurid Saltasaurinae characteriaed by the following association of characters: 1) longitudinal groove located on the suture between parietais thtdt continues posteriorly over the supraoccipital to the foramen magnun; 2) basisphenoid tubera long and narrow (more than twice long as wide); 3) dorsal to middle caudal vertebrae witb deep oval to circular pits on both sides of the prespinai lamina; 4) a n t e r i o r caudal v e r t e b r a with spinopostzygapophysial and spino-prezygapoptiysiai laminae; 5 ) neural arch of anterior caudals witb deep interaygapophysial fossae with numerous pits; 6) anterior caudal vertebra with an accessory sub-horizontal larnina extending from the antero-ventral portion of the postzygapophysis to the mid-portion of the spino-prezygapophysial lamina; finally, 7) anterior caudal vertebra with aprominent axial crest on the ventral surface of the cemtrum.
Elyrnology.The genus is named in honor of Dr. Jos6 E Borlaparte, due to his immense contribution to the knowledge of Mesozoic vertebrates of South America.

Description and Comparisons
The holotype (MACN-PV RN 821) and the referred specimen (MACN-PV RN 1061) were unearthed in the same paleontological site.The remains were disarticulated and the bones of each individual were mixed.The specimens were segregated on the basis of their reiaLive sizes.MACN-PV RN 821 is selected as holotype because it is more conlpiete and the elements preserved are rnore diagnostic than the other specimen.The estimatioa of the body size (mainly based on comparisons of the length between the femora and tibiae) suggest t h a t t h e holotype specimen (MACN-PV RN 821) is approximateiy 20% larger than MACN-PV RN 1061.The description arid comparinons are based on both specimens.The measurements of the postcranial bones are given in the appendix.

Braincasc
Dermal bones and Chondrocranium.Two well preserved braincases are avaiiahie.Most of the chondrocraniuln is preserved in both specimens of Bajo de Santa Rosa, and it is formed by supraoccipital, exoccipital, basioccipital, basisphenoid, parasphenoid, orbitosphenoid, laterosphenoid, prootic, and opisthotic bones.The only dermal bones preserved are the frontals and pa-rietal~.The sutiires are clearer in MACN-PV RN 1061 than in MACN-PV RN 821 perhaps in correlation with the smaller size and younger age of the former specimen.For descriptive purposes, the articular surface of the occipital condyle is posteriorly oriented as it occurs in Rapelosourus krausei, which has one of the better-preserved titanosaur skull (Curry Rogers & Forster, 2001, 2004).
The frontals (Fig. 7) are antero-posteriorly short; they are not fuscd in the sagittal plane as observed in most sauropods (e.Scale bar represents 50 mm.Abbreviations: Bs, basisphenoid; Bo, basioccipitai; bst, basisphenoid tuber; btp, basipterygoid process; ca, crista nntotica; caf, carotid foramen; co, occipikal condyle; cpr, cresta prootica; Eo, exoccipitai; fm, foramen magnum; fo, fenestra oval; Fr, Srontal; jv, jugular vein foramen; Ls, iaterosphenoid; mf, ~netotic fissure; Os, orbitosphenoid; F: parietal; pop, paraoccipital process; Ps, parasphenoid; Soc, supraoccipital; spfr, surfaces ror the prefrontal; spo, surliaces for the postorbital; stf, supratemporal fossa; I-VIII arid XII, cranial nerves foramina. tosh, 1978); in coni:rast, they are fused posteriorly with the parietals.The external surface of the ikontals faces dorsally and forms the anterior border of the supratemporal fenestra as in other titanosaurids ie.g., Antactosaurus, Rapetosaurus and Saltasaurus; Huene, 1929; Curry Rogers & Forster, 2001, 2004;Powell, 2003).On the anterior region of the suture between the frontals there is an inverted au~> shaped tuberosity.On the lateral edge of the frontal there are two articular surfaces: an anterior one for the articulation with the prefrontal and a smaller postero-lateral one for the articulation with t h e postorbital ( t h e prefrontals and postorbitals are not preserved).On the inner side, the frontals have two concave surfaces divided by a sharp and almost transversal crest.The large s t vcntral surface supports m o s t of t h e orhithosphenoid and laterosphenoid, and forms the posterior wall of the orbital cavity; the small dorso-medial surface forms the posterior wall of the olfactory tract and supports the region of the orhitosphenoids where the olfactory bulbs lie.Between the dorsal contact of the frontal and orbitosphenoid there is a transversal groove for the anterior cerebral artery (Berman & McIntosh,1.978).
The parietals (Fig. 7) contribute to the roof of the skull; they are mainly exposed in dorsal view These hones are relatively wider than in Ar~tarctosaurw, hut similar to Rapelosaurus.The parietals are shorter antero-posteriorly than the frontals, and slightly concave.The anterior edge of the parietal forms a crest that deliinits the posterior border of the supraternporal fenestra.The contact of the parietal with the supraoccipital and exoccipital is not observable.In the sagittal plane, where hotti parietals contact, there T h e hasisphenoid forms mainly the basispterygoid processes and a portion of the crista prootica; the sutures among surrounding bones are not observable.The basispterygoid processes of the basisphenoid are long, anteroventrally projected, slender, and less divergent than in Antarctosaurus (in whicti an angle of almost 90 degreos is formed; I-Iucne, 1929); hut for attactlmerit of the axial musculature, defines a longitudinal groove that extends from the parietal to the foramen magnum.The groovc over the parietals is only observable in Bonatilan.
The parietal fontanelle and post-parietal fontanelle are both absent in Bonatitan as in all known titanosaurs.These openings are only developed in llicraeosaurus and Amargasaurus (Janensch, 1935-36;Salgado & Calvo, 1992).
The parasphenoid is broken in both specimens, hut according to the preserved base ofthe rarnen magnum.On the posterior surface the supraoccipital bears a longitudinal groovc that reaches the foramen magnum (see also above).This groove is also present in Rapelosaurus (Curry Rogers & Forster, 2004) but apparently it does not extend anteriorly on the parietal as in Bonatilan.In Anctartosaurus (MACN-PV 6804) the supraoccipital forms a distintive process but a longitudinal groove is riot evident (Huene, 1929; contra Curry Rogers & Forster, 2004).The dorsal edge of the foramen magnum in MACN-PV RN 821 is rnore concave than in MACN-PV RN 1061.
Thc hasioccipital (Fig. 7) forms the occipital condyle, which is prominent and almost spherical.We follow tile interpretation ofRapetosaurus (Curry Roger & Forster, 2001,2004) in which the occipital condyle is posteriorly projected rather than postero-ventrally a s in Brachiosaurus (Janensch, 1935-36, 19501, or ventrally as in dicraeosaurids and diplodocids (Salgado & Calvo, 1992;Berman & McIntosh, 1978).The orbitosphenoids (Figs.7C, 8 ) face anterolatcraly and are pierced by several foramina for the exit of the cranial nerves (see below; Fig. 8).In anterior view, the orhitosphenoids meet cactl other; posteriorly they are partially fused with the latcrosphenoid and dorsally they are in contact with the frontals.
Sutures of the laterosphenoids (Figs.7C, 8) with the parasphenoid, hasisphenoid, and otic bones are not discernible.The laterosphenoids project laterally contacting dorsally with the frontals; contributinganterolaterally to the crista antotica.Above the crista antotica, near the frontal, there is a depression with a small foramen for the mesencephalic vein (Berman & McIntosh, 1978).
There a r e no clear sutures hetween the exoccipital and the surrounding hones of the skull (Fig. 7).The paraoccipital processes are prominent, ventrally projected, and hear a roughly lateral surEace for the articulation with the squamosal as in Saltasaurus.These processes are situated at the same level of the occipital condyles as in other titanosaurids (e.g., Antactosaurus and Rapetosaurus), with the exception of Saltasaurus where they occupy alower position (i.e., they are longer and more ventro-anteriorly projectod).The paraoccipital processes are <<C>.-shaped,a condition similar to that found in Saltasaurus, Antarctosaurus, and Rapetosaurus.
The prootic and opisthotic bones are strongly fused.Tile crista prootica is thin and dorsally delirnits the niiddle ear cavity, which is deep and postero-ventrally faced.The fenestra oval, which accommodates the footplate of the stapes, is oval-bitosphenoid and laterosphenoid, and laterally faced.The anterior rim is straight with a welldefined border, while the posterior border is slightly concave . I n Antarctosaurus (IIuene, 1929) and Saltasaurus (Powell, 2003) this foramen is oval in shape.
The optic foramen (CN 11) pierces the orbitosphenoid; it is an oval-shaped opening, facing anterolateraly, and larger than the fbramen for the oculomotor nerve (CN 111); this morphology is similar t o S a l t a s a u r u s (Powell, 1.9861, Quaesitosnurus (Kurzanov & Bannikov, 1983), and Rapetosai~rus (Curry Rogers & Forster, 2004).I n C a m a r a s a u r i ~s (White, 1958), Diplodocus (Berman & McIntosh, 1978), Rebbaclzisaurus (Calvo & Salgado, 19951, and Amargasaurus (Salgado & Calvo, 1992) the optic and oculomotor foramina are considerably smaller and almost equal in size.In the specimen MACN-PV RN 1061 the optic foramen is relatively smaller than in MACN-PV RN 821.
The ahduceris foramen (CN VI) is sinall and ioca~ed ahove and anterioriy lo the carotid foramen.Based on other sauropods this foramen should he located at the level of the suture between the orbitasphenoid and paraspherioid (but t h i s s u t u r e is not clearly discernable in Bunatitan).
The faciai foramen (CN VII) is small, eye shaped, and anteriorly faced.It is surrouiided dorsally by the aiispiicnoid and ventrally by the prootic.This opening is located on tho crista prootica below the foramen for the CN V The acoustic foramen (CN VIII) is circularshaped, siriallcr than the facial forameii, and placed in the middle ear cavity dorsal to the fcriestra ovalis.
The glossophilryngeal (CN 1x1, vagus (CN X), and accessory (CN XI) rierves, and the jugular vein pass through the metotic fissure (De Beer;1937) on the posterior wall ofthe middle ear cavity This fissure is the largest opening of the lateral wall of the braincase, located postero-ventrally to the fenestra ovalis; both openings are separated by a thin bony wall.The hypoglossal foramen (CN XII) opens in the exoccipital, posterior to the base of the paraoccipital process, and outside of the middle ear cavity.
The carotid foramen is fully enclosed in the basispterygid process.This opening is smaller than that of Saltasaurus and Antactosatlrus.Near the carotid fbramen a small indeterminated foramen is present.

Postcranial skeleton
Cervical iierlebra.The cervical vertebra (Fig 9) consists of a n anterior centrurri strongly opisthocoelous with the parapophyses located on the anterior half (the neural arch is not preserved).The centrum is almost as high as wide and very antero-posteriorly elongated, even more so t h a n S a l t a s a u r u s (Powell, 1986(Powell, , 2003;;Bonaparte;1999) a n d I s i s a u r t ~s ( J a i n & Randyopadhyay, 1997;Wilsori & Upchurch, 2003).Ttic pleurococls, placed above the posterior edge of the parapopkiyses, are oval and deeper than in Sallasaurus.The pleurocoels are divided by an oblique septum, also present in Saltasaurus (Powell;1986,2003).The parapophyses are thin and iatero-ventrally oriented.Due to the relative sniall size, this centrurri is tentatively assigned to the srnallcst specimen (MACN-PV RN 1061).Dorsal vertebra.An almost coinplete dorsal verl.cbra (Figs. 10,11) was recovered and based on the size it is assigned to the holotype.The left postzygapophysis and the distal portion of the neural spine are preserved and hroken from the rest oi'the t~eural arch (Fig. 12).We interpret this eleincnt as a iniddie dorsal vertebra due to the possession of a deep postparadiapophyseal fossa (sms:i Ronaparte, 1999; fossa placed posteriorly to the anterior centroparapophyseal lamina of Wilson, 1999); and because t.kie g~arapophysc.%$are high and anterior to t h e diapophyses.The larger antero-posteriorly t h a n wide.The pleurocoei is deep and eye-like shaped with well delimited edges as in Ne~~quensaurus (Powell, 2003); in Saltasaurus and isisauras (Jain & Bandyopadhyay, 1997;Wilson & Upchurch, 2003) tile anterior and veritral edges of the pleurocoel slope gradually.Tkie neural arch and the centrurn are separated; both elements tiave cancellous osseous tissue.The posterior ccntrodiapophyseal larnina (pcdl) (infradiapophyseal lamina sensu Bonaparte, 1999) is thin and vertically reaches tfic centrum a t the posterior region a s in the middle dorsal vertebrae of Saitasaz~rus and 1Veuquensaur:is.The thin anterior centroparapophyseal lamina (acpl) runs almost parallel to the posterior centrodiapophyseal lamina (pcdl).The articular surface of the parapophysis faces laterally and is nearer to the preaygapophysis tkian to the diapophysis.The prezygapophyses are located at the sarne level as the parapophysis, hilt face dorso-medially The centropre~ygapophyseal larnina is ahseiit as in Neuquen,saurus (Powell, 1986(Powell, , 2003) ) a n d Rocasauras (Salgado & Aapilicueta, 2000).The postparadiapophyseal fossa (pparf? is deep and constitutes the most remarkable feature in lateral view The diapophyses are slender and are directed latero-dorsally.The postzygodiapophyseal lamina (podl) (diapopostzygapophyseal lamina sensu Ronaparte, 1999) is slender and hears on its dorsal surface some oval depressions arid pits, a unique feature  among titanosaurs.Tile infrapostzygapophysial sprl+prsl sensu Wilson, 1999) is thin (however lamina (tpol) is thin and incompletely preserved.it is badly preserved in the fragment of the neu-The infrapostzygapophysial fossa is deep and ral spine).Thc undivided neural spine has its faces posterolateraliy I n the basal portion of the right half portion broken off (Fig. 12); it seems n e u r a l arch t h e prespinal lamina (prel) to he transversely wide anddorso-ventrally short.
(spinoprezygapophyseai plus prespinal laminae, In anterior view, the prespiilai lainiria separates two deep lateraldepressions (Fig. 12A).This portion of the rieural a r c h preserves the left postzygapophysis, viliich is extremely hollow as shown in f i ~i r e 12, and its articular surface is latero-ventrally oriented.
Caiidal r;ertebr.ae.The almost coinplcte anterior caudal vertebra  and the rielirai arch of a middle caudal vertebra (Fig. 16) are preserved; they are considered to belong to the largest specimen (MACN-PV RN 821).
On the lateral aspect of the anterior caudal vertebra, above the axial crest, the lat,cral surface of the ccntriim is dorso-ventrally convex.Oriiy the bases of both diapophyses an.preserved.The circular shaped neural canal is longer than those preserved in the caudal vertebrae of Salta,saurus.Tlie neural spine is low, similar to Sa1tasai~1.u~.'She prespiiial lamina (prel! is thin, bearing well-detincd oval pits on both concave latel.;ilsides.The spinoprexygapophyseai (sprl) and the spinopostzygapophyseal (sposl) iarniiiae are well-defined, and between each there is a deep and large interaygapophyseal fossa divided by a sub-horizontal accessory lamina (acl!.The dorsal interaygapophyseal fossa extends dorsally, above the level of the postzygapophysis.The ventral intcrzygapophyseal rossa is smallar and shallower, extending ventrally to the level of the prezygapophysis.Inside both Sossae there are subcircular pits similar to those present lateral t,o the prespi~ial lamina. The prezygapophyses are anteriorly directed, and the articular surfaces Sace dorso-mediaily.The postxygapophyscs are located at the level of the posterior edge orthe neural spine.The postspiilal lamina ipostl!(medial spinnpostaygapoph-jseai plus postspinal laminae, med.spol i -posl, sensu Wilson, 1999) is wider than the prespinal one.
The middle caudal neural arch (Fig. 16) is not cornplot,ely fused to the vertebral centrum.Tlie neural spine is short, rohost but extremely hollow, and steeply inclined backwards.The anterodorsal corner ofthe spirle is at the sanie level of the posterior edge of the postzygaphopliysis as in Sollusauri~s,Nei~q~~e~~,sauriis, and Rocasauriw.(Fig. 17).This feature was considcred a synapomorphy of the Saltasaurinae (Salgado et ol, 1997a).The prespirial lamina divides two deep depressions, as occurs in the neural arch described above.Inside these depressioiis there are deep pits decreasing posteriorly insize.Asimilar feature, but not as de-    veloped as in this new species, is observed in the middle caudal vertc!brae of Neuquenwurus (Powell, 2003: Plate 58).The prezygapophyses are prominent, antero-dorsally directed with the articular surfaces dorso-metiidly exposed.The postspinal lamina is more prominent and robust than the prespinal one.Between both postzygapophyses, at the base of' the postspinal lamina, there is a deep fossa similar to Neuquensaurus (Powell, 2003).
Humerus.A complete left humerus (Fig. 18A) was recovered and assigned to the halotype.The humerus is more slender than in Neuquensaurus and Saltasaurus (Huene, 192% Powell, 1986,1992, 2003).The hnmeral head and deltopectord crest arc poorly developed similar to Laplatasaurus (Huene, 1929), Lirainosau?-us (Sanz et al., 1999), and Rapetosaurus (Curry Rogers & Forster, 2001); instead, Neuquensaurus and Saltasaurus have a more p r o m i n e n t head a n d robust deltopectoral crest.The shaft is narrow and the proximal end is wider than the distal one.The proximal end is slightly rotated in relation to the distal one.Both distal epicondyles are not well developed.The humerus length relation with the fernur is approximately 0.8.
Ulna.The left ulna (Fig. 18B) is cornpletely preserved and belongs to the smaller specimen (MACN-PVRN 1061).This element is moreslender than in Neuquensaurus and Saltasaurus (Huene, 1929;Powell, 1986Powell, , 1992Powell, , 2003)).The proximal end is rugose, slightly convex and subtrianyuiar, with a concave proximal border of the radial fossa (Fig. 18B).The olecranon process is absent.Proximally, the antero-lateral surface of the ulna is concave for the articulation with the radius.The posterior surface of the shaft is almost plane and bears a ridge on its distal half that ends near the distal end.The distal surface is also rugose, rectangular in cross section, and transversely narrower than the proximal end of the bone.
Radius.A left radius is incompletely preserved and also belongs to the smaller specimen.The proximal end is broken on ttie antero-medial edge.The shaft is oval in cross section, and  (Salgadoet al., 199%;Wilson & Sereno, 1998).The femoral head is rather medial than dorso-medially projected.The medial border or the femoral ral shaft; there is an intercondylar notch betwean ahern.Tibia.Both tibiae (Fig. 18D) were recovered for the holotpe, while only theleibone for the referred material (Fig. 18E).The tibia is nearly 12%, smaller than the femur The proximal end is antero-posteriorly narrower than in Neuquensau,sus and Sallasaurus (Huene, 1929;Powell, 1992Powell, ,2003)), and quite similar toLaplatasaurus (Huene, 1929).The cnemial crest is thin and poorly developed, differ--~ head is more curved in ./LACN-PVRN 1.061 (as in ingfrorn Neuquensaurus and Sulta,saurus in which Saltasauras and Neuouensaurus: Powell. 1986. it is robust and nrominent.The distal end is trans-2003) than in the hdlotype.The greater tro: chanter is located a t the level of the head, and the fourth trochanter is not evident.The tibia1 condyle is niore prominent and more distally developed than the Fibular one as it is observed in Neuquensaurus and Saltasat~rus, but different from Rocasaurus that has similar sized condyles (Salgado & Aspiiicueta, 2000).Both condyles are expanded onto the anterior surface of the femo-versely broad as in other titanosaurs (Salgado et al., 1997a).The main axis of the proximal surface has a relation of aproxinlately 90' with the main axis of the distal surface, similar to Sultasaurus and Neuquensaurus (Powell, 1992;Sanz el al., 1999).
Fibula.Only the complete left fibula (Fig. 18F) assigned to the holotype is preserved.This is a relatively straight and slender bone with a  1992); E. Ilocasaur~zas mzcniozi (modified from Salgado & Azpilicncta, 20003; F Bonatitan reigi gen et sp.nou.Scale bar represents 50 mrn weak antero-lateral tuhcrosity located above the middle of the shaft.The proximal articular surface is trian~qbar; in contrast, ,the distal one is oval.This bone is slightly shorter than the tibia. Metatarsal I.The left metatarpal I is assibned to the holotype specirneri.This bone is short and robust (Fig. 18G).The proximal sureace is slightly convex and subrectangular with the posteroniedial corner posteriorly projected.The posterior surface of the shaft is coilcave and the anterior one is almost straight.The shaft is transversely narrow The distal surface is also rectangular with the lateral area distally projected.This metatarsal closely resembles that of A~euquensu.ori~s (Huene, 1929) andAeolosaurus sp.(Salgado et al., 19971)), with the shsfa more slender than in Ar~tur-ctosaurz~s (Huenn, 1929).
Metatarsal 111.This metatarsal is smaller in comparison to rnetatarsal I and it is assigned i.o the smallest specimen (MACN-PV RN 1061).The proxirnal surface is triangular, antero-posteriorly elongated, and slightly convex.The distal surface is rectangular and transversely wide.The narrower section of the shaft is located in the lower half of the hone.The anterior surface is flat while the posterior one is strongly concave.

Comments of Bonatitan reigi
The subfamily Saltasaur~nae, proposed hy Powell (1986), was pi~yiogenetically defincd as the clade that includes the more recent common ancestor of Neuyuensaurus a u s t r a l i s and S a l t a s a u n ~s loriculus, and all its descendants (Salgado et al., 19978).This group was originally diagnosed hy Salgado el al. (1997a) based on the following derived features: a) short cervical prezygapophyses near the level of the diapophyses; b) depressed anterior caudal cerltra, with dorsovei~trally corivex lateral faces; and c) anterodorsal edge of the neural spine located posteriorly with respect to the anterior root of the middle-caudal postzygapophyses.In addition, the presence of cancellous osseous tissue in presacral and anterior caudal vertebrae was considered another synapornorphy of Saltasaurinae (Powell, 1986).
Curry Roger & Forster ( 2001) interpreted Saltasaurinac as a more inclusive taxon, which includes Alamosaurus, Titurlosat~i-us, Opisthocoelicaudia, Neurjuensaorus, and Sallasaurus.These taxa were nested together due to the presence of four unambiguous traits: biconvex first caudal centrurn, deltopectoral crest reduced to a iow rounded crest, mar.ual digits 11 and I11 witilout phalanges, and proximal breadth of the tibia more than twice its nlidshaft breadth (Curry Roger & Forster, 2001).Wilson (2002: 269) interprct.edS a l t a s a u r i n a e a s composed by Neuquensourus plus S a l t a s a ~~r u s , sharing four uncquivocals features: cervical neural arch iainination well developed; spongy caudal hone texture; posterior caudal centra dorso-ventrally flattened; and femoral distal condyles exposed on the anterior portion of the fen~oral shaft.This subfamily together with Opist.hocoelicaudiinac,comprise the family Saltasauridae proposed by Sereno (I 998) in replacement of TiLanosauridae.
Later, in order to clarify the term Titanosauridae, Salgado (2003) reviewed and estahlished a new taxonomic proposal for the highertaxa of Titanosauria.In his work, the family Titanosauridae was justificated as a valid name, instead ofsaltasauridae (see Salgado, 2003).Also, Salgado (2003) redefined Saltasaurinae as all the cutitanosaurs closer to S o l t a s a ~~r u s than to Opisthocoelicaudia (following the interpretation of Sereno, 1998;Wilson, 2002;Wilsori & ijpchurch, 2003).In addition, Saltasaurinae and Opisthocoelicaudiinae (Sereno, 1998) are nested within the stem-based taxon Eutitanosauria (proposed by Sanz et al., 1999).
Bonatitarb reigi is here considered as a new Saltasaurinae because it exhibits the following diagnostic features of the subfamily: 1) Antero-
3) Cancellous osseous tissue in the presacral and caudal vertebrae, mainly observed in the neural arches.Other syriapornorphies of Saltasaurinae such as the presence of short cervical prezygapophyses and depressed proximal and middle caudal centra is unknown in the two available spccirnens of Bouatitan.The only caudal centrurn preserved in Bonatitan is not dorso-ventrally dcpressed, instead it bcars a prominent axial crest on the ventral surface that is interpreted to be an autapomorphy of this new species.Amongsaltasaurines, the appendicular bones of Bonatitan reigi are more slender than those of Saltasaurus and Neuquensaurus, taxa in which these elements have a more robust aspect with well developed processes (e.g., cnernial crest in tlie tibia).The femur is the only appendicular hone that can be compared with Rocasaurus; it is quite similar in both species, only differing in the relative size of t h e distal condyles (in Rocasaurus a r e almost equal, whereas in Bonatitan the medial condyle is larger than the lateral one).Thus, the appendicular bones of Bor~atitan (and aiso of Rocasaurus) show a more " -1971), Quaesitosaurus orientalis (Kurzanov & Bannikov, 1983), Iiapetosaurus krausei (Curry Rogcrs & Forster, 2001, 20041, Lirainosaurus aslibiae (Sanz et al., 1999), and unnamed taxa from India (Berman & Jain, 1982), Europa (Le Loeuffelal., 198% Weishampclet al., 19911, and Argentina (Calvo et at., 1997a;Martinez, 1998;Coria & Salgado, 1999).Controversial liypotlicses concernirig tht? skull morphology (a diplodocid or camarasaurid aspect), orientation and relationship of the skull bones (McTntosh, 1990;Calvo, 1994;Jacobs el al., 1993;Salgado & Calvo, 1997;Upchurch, 1995Upchurch, , 1999) ) were partially clarified after the discovery of Rapetosaurus krausei (Curry Rogers & Forster, 2001, 2004;Wilson, 2002), wliicli has the best preserved and fairly complete skull arnorrg titanosaurs.
'She skull of Bonatitan shows some differences with regards to Saltasaurus, including unfiisttd basipterygoid tubera of the hasisphenoid (in Saltasaurus these are thick arid fused; Powell, 1992Powell, , 2003)); paraoccipital process located at the same level ofthe occipilal condyle (in Saltasaurus they are below that level); and reduced and posteriorly placed carotid foramen.In Bonatitan, the basipterygoid tubera are twice dorso-ventrally longer than transversely; in contrast, Antarctosaurus and Rapetosaurus have robust and short tubera almost as long as wide (Huene, 1929;Curry Rogers & Forster, 2004).The basipterygoid processes of the basisphenoid are divergent in Bonatitan, while in Antarctosaurus they almost form a straight angle and in Rapetosaurus they are almost parallel.In consequence, the main axis of the basipterygoid tubera coincides with the main axis of t h e hasipterygoid processes in Antarctosaurus, while in Bonatitan a n d Rapetosaurus the basipterygoid tubera are more divergent than the basipterygoid processes.
Among t i t a n o s a u r i d s only B o n a t i t a n , Saltasaurus, Antarctosaurus, and Rapetosaurus have a large trigeminal foramen (CN V).This foramen is very reduced in Quaesitosaurus (Kurzanov & Bannikov, 1983) and the other nontitanosaurid neosauropod (e.g., Madsen et al., 1995;Berman & Mclntosh, 1978).The optic foramen is relatively Large in Bonatitan, Saltasaurus, Quaesitosaurr~s, andRapetosaurus while i l is reduced i n o t h e r neosauropods such as brachiosaurids or dicraeosaurids.The overall comparison with others titanosaurids suggest that the cranial morphology of Bonatitan Faveoloolithidae Zhao & Ding, 1976 Sphaerouum erbeni Mones, 1980 (Fig. 19) ReferreclMaterial.MACN-PV RN 1088: thousands of isolated eggshell fragments and seven eggs almost complete.
Description.The eggs are spherical and the diameter varies from 180 to 210 mm.The eggshells are thick and vary from 5 to 6 mm.The morphotype is filispherulithic (small narrow spherulites that converge one with another leavingsurroundingpores; Mikhailov, 1991); the eggshells have a multicanaliculate pore system (Mikhailov, 1991).
Comments.The eggshells here described have a iilispherulithic morphotype, a multicanaliculate pore system, and compactituherculate oxtcrnal ornamentation, a set of features diagnostic of the species Sphaerouum erbeni Mones (Casadioet al.,
Referred Material.MACN-PV KN 1096: fragments of eggshells and eight partial eggs.
Description.These eggshells are thin (about 2 mm trick) and scarcer than the Faveoloolothidae.The more complete egg is subspherical, approximately 120 mm in diameter.The external surface is covered with spherical, dome-shaped tubercles that are tightly in contact each other.This type of compactituhercnlate ornamentation is common in et al., 2002).The morphology of the shell in these remains is tubospherulithic (shell units sharply Both the Megaloolithidae and Faveollolithidae oofamilies were recognized in these beds (e.g., Mones, 1980;Powell, 1987aPowell, & c, 2003;;Chiappe et al., 1998;Casadio et al., 2002).The eggshells preliminary reported from the Allen Formation were assigned t o Sphaerouum erbeni (Faveollolithidae) (Casarlio et al., 2002).I n 1990 a great abundance of eggshells and nests in the areaof the Bajo de Santa Rosain the upper member of the Allen Formation were discovered indicating an important sauropod nesting ground.Posteriorly to the discovery, this region was looted and the fossiliferous richness of eggs and eggshells decreased drastically . .

tubucanaliculate pore system
Comments.The tuhospherulitic morphology of these remains suggests megaloolithid affinities and clearly indicates the presence of another taxon different to Sphaerouum erbeni.

TEEKOPODS
The record of theropod dinosaurs in the Allen Formation is scarce in comparison with other Cretaceous formations of Patagonia.T h e theropods described from the Allen Formation are the abelisaurid Quilmesaurus curriei (Coria, 2001;Kellner & Campos, 20021, and a yet (Fig. 20A) Referred Material.MACN-PV RN 1086: an isolated tooth.
Description.The orily noxi-avian theropod remains report,ed in this present study consists of a small serrated tooth represented hy a fragmentary crown (Fig. 20A).For descriptive purposes the most convex serrated edge is interpreted as mesial and LLi e most flat surf:lce of the tooth as lingual (i.e., the tip of the tooth is inclined distally and lingually).
The preserved crown height is 19 mm, with a maximum mesio-distal width of I1 mm a t the base.The mesial carina is slightiy more curved than the distal one.The carina bears about 9 denticles in 5 nim.Well developed blood grooves are present between succcsive denticles as occurs in Carcbarodontosauridae, Tyrannosauridae, Dromaeosauridae, and Allosaurus (c.g., Currieet al., 1990).The crown is transversely narrow at the top, but wide a t the botton.The labial surface is dorso-ventrally and mesio-distally convex.The tip of the crown is slightly inclined lingually On both surfaces, close to the mesial and distal edges the enamel is wrinkled, forming obliquely oriented barids that extend fro111 the carina to the midline of the crown.These bands are more evident on the lingual side (Fig. 20A).
Comments.Thc wrinkled condition of the enamel leads us to consider this specimen as cf Carcharodoritosauridae, a feature that was interpreted as diagnostic for the family (e.g., Sereno et a l . , 1996;Larsson, 1996;Candeiro, 2002).Nevertheless, it is worth mentioning that carcharodontosaurid teeth has a height of approximately 100 mm, differing considerably with regards to the very small taxorl described here.
The record of a tentatively Carcharodontosauridae in the Allen Formation a t the Bajo de Santa Rosa locality is a significant find because tlie largo sized members of this family (e.g., Giganolosaurus carolinii, Carcharodontosa~~rus saharicus; Coria & Salgado, 1995;Sereno et al., 1996), which proliferated during the Aptian-Tnronian times in South America and Africa, are poorly represented in the fossil record during the Coniacian to Maastrichtian times.
If the wrinkled enamel of carcharadontosaurids is a diagnostic trait not recordered in others neotheropod taxa, this tooth could represent the first record of the family in the Campanian-Maastrichtian of Patagonia, and together with those specimens from the Maastrichtian Marilia Formation (Brazii; Candeiro et al., 2002) may suggest the persistence of this family throughout the uppermost Crelaceous in South America.

ORNITHISCHIANS
The occurrence of ornithischian dinosaurs in the Allen Formation is based on vertebral and sacral remains of a Lambeosanrinae (Powell, 1987h) and a few isolated bones and dermal plates of a probable Nodosauridae (Ankyiosanria) from Salitral Moreno, Rio Negro Province (Salgado & Coria, 1996;Coria & Salgado, 2001), and fragmentary postcraniirl elements of a Hadrosauridae (closely related to Kritosaurus australis) frorn the west of La Pampa Province (Gonzaiez Riga & Casadio, 2000).
Among the families identified here, specimens of continental (terrestrial and fluvial) and marine environments are docurnented.Fresh water taxa include Dipiomystidae, Percichtyidae, Lepisosteidac, dipnoan lungfishes, pipid frogs, and cllelid turtles, whereas terrestrial taxa include nladtsoiid snakes, sphenodonts, hadrosaurid, theropod, and titanosaurid dinosaurs.Living ieptodactylids inhabit both terrestrial as well ai; freshwater environments; nevertheless, the closer affinities between the specimens ofthe Allen Formation and the strictly aquatic living genus Caudiuerbera t h a t livas in rivers and streams (Cei, 1962) suggests the presence of another freshwater taxon.
The marine taxa are scarce and fragmentary, and represented by a t least one Laxon of Elasmosauridae plesiosaur Within plesiosaurs, this family was interpreted as reiated to coastal environments (Gasparini et al., 20011; disarticiilated remains are lrequently fourid in association with continental vertebrates (c.g., Gasparini & Salgado, 2000;Gasparini et al., 2001).
Some of the dinosaurs found at Bajo de Santa Rosa arc often associated with mixed environments.IIadrosaurids and some sauropods were frequently recovered in coastal rilarine environments (e.g., shallow marine or estuarial deposits; Horner, 1979; i u c a s & H u n t , 1989; Weishampel & Iiorner, 1990;Dodson, 1990;L6pez-Martinez et al., 2000).The two types of eggs (Faveoloolithidae and Me~aloolothidae) re-"-" and Rio Negro Provinces (Argentma) This tinit he restricted to a water-satured atmosphere or wetlands (e.g., Seymour, 1979).Megaloolithidae remains were frecuently documented in low-gradienl floodplain erivironments in the Rio Colorado Subgroup 0f' Neuqui.n (Dingus et al., 2000) as well as in tidal flats (near sea shore) environment from the Late Campanian of Spain (Lopez-Martinez et al., 2000).Thus, both types of eggshells indicate a wet and low land environment.
The evidence of the vertebrates presented here collected a t Bajo de Santa Rosa is con&.ruentwith the paleoenvironmental reconstruction of the Allen Formation based on geological stndies: a continental environment developed close to a marginal-litoral place (Andreis et at., 1974 ;Casamiquela, 1978;Uliana & Dellap6, 1981 ;Barrio, 1990;Casadio, 1994;GonaBlez Riga & Casadio, 2000).This paleoenvironmental reconstruction explains the mixed association of vertebrates i:ornposed by terrestrial, freshwater, and marine coastal taxa.
In addition to the vertebrate remains recovered at Bajo de Santa Rosa, fossil wood (Andreis el al., 1991), palm fruit (Ancibor, 19951, and two species oFPodocarpaceae conifers (Ccrcoporoxylon greg~rssii andPodocarpoxyEongarciae; Del Fueyo, 1998) in the Alien Formation indicate the presence of a continental environment.
The invertebrate fossils such as gastropod, bivalves, ostracods, hriozoans, and foraminifera collected near the Bajo de Santa Kosa, Salitral O,jo de Agua, Cerro Mesa, Bajo de Los Menucos, and Lago Pellegrini localities suggest fresh water to salty Lagoons; whereas the presence of the briozoan Fungela in some localities (Salitral Ojo de Agua and Lago Pellegrini) into the uppermost level of the Allen Formation (near the contact with the marine Jaguel Formation) indicates marine conditions (Wichmann, 1.927;Ballent, 1980;NBhez & Concheyro, 1996;Echevarria, 1999;Nhfiez, 1999).As previously mentioned, it is clear that the Alien Formation (and also the Loncoche Formation) represents the transition between the fully continental Neuqu6n Group and the fully marine Jaguel Formation (Malargue Group) in nortliern Patagonia (e. g., Page et al., 1999; and references here cited)

Comments about Campanian-Maastrichtian South American vcrtebralebearing formations
Most of the vertebrates discovered in the lower member of the Allen Formation represent taxonomic groups of Gondwanan affinities (Bonaparte, 1986b)  ture of taxa has been correlated with tha connection between South America and North America through Central America a t the end of the Cretaceous ie.g., Anderson & Schmidt, 1983;Ronaparte, 19866).
The available evidence from Campanian-Maastrichtian vertebrate-bearing formations of South America provide a more complex and diverse vertebrate association than that reported until the present in other Gondwanan localities.The entire information available from several units of South America such as the Loncoche, Los Alamitos, La Colonia, Los Blanquitos, Yacoraite, El Molino, Adamantina, and Marilia formations show a similar fossil vertebrate composition, with relatively few differences between t h e Patagonian and extra Patagonian South American records (Table 3).
A preliminary comparison a t a supragenericdl level suggest strong affinities among the South American vertebrate-bearing units (Table 3) Nevertheless, some taxonomic groups are only restricted to one geographical region; fbr exanlple Chelidae, Meiolanidae, Sphenodontia, Gondwanatheria, and Muitituberculata are until now unly recognized in Patagonia.These differences observed in the taxonomic compositon of thc vertebrate assemblages of Patagonian and extra-Patagonian regions could be artificial due to the u be evaluated cautiously.
The Dryolestoidea is a t the monicnt tlie most diverse and largely documented group of nontribospbonic mammals recognized in several Late Cretaceous localities of South America.Campanlan-Maastrichtian Palagonian dryolestoids are widely docuniented in the I,os Alainitos (Bonaparte, 1966a(Bonaparte, , 1990(Bonaparte, , 2002) ) and L>a Colonia formations (Rougier et al., 2000(Rougier et al., , 2001)), and only a few specimens were recently found in the Allen Formation (Rougier el al., 2003).
Older possible dryolestoid reports from Patagonia come from the Santonian Portezuclo Formation (Neuquen Group; Neuquen Provincc; Coria et al., 2001;Coria, pcrsonal comrnunication); in addition, another specimen originally described as a pruhable marsuipial (Goin et al., 1986) fiom the Anacleto Formation (Neuquen Group; Paso Cordova, Rio Negro Province) could be tentatively assigned to the Dryolestoidea.The jaw of the Paso Cordova specimen is high with the ventral edge slightly convex and transversely rounded, the masseteric fossa is deep, the lingual alveolar level is set notahiy more ventrally than the lingual one, the alveoli decrease backwards and are transversely wide and very ailtero-posteriorly short resembling the condition of Ida ,<Banco Negro Inferiorn of the Salamanca For-mation (Chubut Province, Argentina).These features suggest that tile mammal of the Anacleto Yomiation probably corresponds to a dryolestoid.Analyses based on the mammalian fossil record of the Los Alamitos and La Coionia formations liave considered that they are probably enderriic to Patagonia (Enson & Sigogneau-Xusscll, 1999;Rougier et al., 2000Rougier et al., ,2001)).In contrast, Bonaparttl (20021, based not only on the record of mammals hut also in other vertebrates, criticized this hypothesis concluding that t.he Patagonian mammals are not endemic but a sample of widespread Gondwanan lineages (Bonaparte, 2002).Recent discoveries of mammals with dryolestoid affinities in the ,Maastrichtiari El Moliiio Formation of Bolivia (Gayet et al., 2001) support the later interpretation.

CONCLUSION
The vertebrate fossil remains discovered a t the Bajo de Santa Rosa locality, Rio Negro Province, Argentina (Table 1 and 2) provide new data about the diversification and compositional vert e b r a t e assemblage of t h e Campanian-Maastrichtian Allen Formation (Malargiie Group).
Among fishes, the Allen Formation has provided the most southern and possibly the eariisphenodont and a possible survival carcharodontosaurid theropod are also recognized.The Madtsoiidae are the dominant snakes in the Alloil Formation.We recognized Pataganiophisparvus Albino and Alamitophis argentinus Albino, and a possible new taxon of 7Madtsoiidae.The taxonomic position of Rionegrophis madtsoioides proposed by Albino (1986Albino ( , 1987) ) a s a possible Madtsoiidae is supported after new discoveries fi.ornLos Alamitos.A new saltasaurine titanosanrid, Bonatitan reigi gen, et sp, nou. is described and compared.
The vertebrate record is mainly composed of continental (terrestrial and ikeshwater) taxa, and a few marine elerncnts (elasmosanrids) indicating the influence of the sea during the deposi-tion of the Alien Formatioil in the area of Ua.io de Santa Rosa.
The vertebrate remairis support a Campanian-Maasarichtian age for the Allen For~nation.Comparisons with o t h e r South American Campanian-Maastrichtian localities suggest a similar fossil vertebrate composition, with relatively few differences between the Patagonian and extra Patagonian South American records.

Fig. 1 .
Fig. 1. .I. Location map ofthe Bajo de Santa Rosa locality, lZio N e b ~o Province, Argentina; B. geological map at Bajo de Santa Rosa (modified from Hugo & Loanza, 2001).Regular dots indicate the outcrops ofthe Bajo de la Carpa Fori~~ation; grey pattern indicates the Allen Formation; and horizontal stripes indicate tlie J a ~i i e l Formation.The arrow shows outcrops at Bajo dc Santa Rosa where thefossils were collected.

-
Until recently discoveries of abundant remains in the Late Triassic of Braaii(Ferigolo,   Referred Material.MACN-PV RN 1062: a 2000: Bona~arte, personal communication) and middle uortiori of the ric~lit lower iaw.
in the Early Eocene of Australia(Sca~llon, 1993).The new record in the Bajo de Santa Rosa locality expands the temporal and geographic distribution of this species during the Cretaceous.Madtsoiidae Hoffstetter, 1961Alamitophis argentinusAlbino, 1986  (Fig. 5B)   Referred material.MACN-PV RN 1053: incomplete trunk vertebra.

Fig. 18 .
Fig. 18.Bonatitan rezgi gen et sp.nou.Rolotype MACN-PV RN 821, pilotographs of A. left hum in posterior view; B. left ulna in posterior and proximal views; C. left fernur in anterior view; D tibia in lateral and medial views; E. left tibia in lateral vicw (juvenile specimen MACN-PV 1061); ' Icft fibula in lateral view; G. loft metatarsal I in lateral, medial and posterior views.I bar represents 50 mm.Figs.A, C-F are at the same scale.
of the nostzveanoahvses in the middle cau-19931.N e m e ~t o s a ~~r u s moneolienisis(Nowinski.
Fig. 21.Squematic reconstruction of the landscape at Bajo de Santa Rosa, Rio Negro Province, Argentina, during the Late Cretaceous Allen Formation.Drawing made by Jorge L. Blarrco.
Marlinelli & Forasiepi sp.nou.Diagnosis.As for the genus.Etymology.The species is named in honor to Dr. Osvaldo Reig for his contribution to South American paleontology Nolotype.MACN-PV RN 821: complete hraincase, middle dorsal vertebra, anterior caudal vertebra, middle caudal neural arch, left humerus, fragment of metacarpal, both femora, both tibiae, left fibula, left calcaneous, left metatarsal I, and some fragmentary elements.
represented by an almost complete skeleton from the Albian-Cenomanian Candeleros Formation of Neuq~iiin.
Table of measurements of the postcrBnial banes of Bor~atitan reigi gen, et sp, noo.An asterisk (*)indicates a n estimated measurement.