Arquivos do Museu Nacional, Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 ISSN 0365-4508 A NEW TITANOSAUR SAUROPOD FROM THE LATE CRETACEOUS OF NEUQUÉN, PATAGÔNIA, ARGENTINA 1 (With 14 figures) JORGE O. CALVO 2 * BERNARDO J. GONZÁLEZ-RIGA 3 JUAN D. PORFIRI 2 ABSTRACT: The discovery of Muyelensauruspecheni gen. et sp.nov., a new slender titanosaurid, is relevant from anatomical and systematic viewpoints. The specimens come from the Upper Cretaceous strata of the Portezuelo Formation (Turonian-Early Coniacian) at Loma dei Lindero, Rincón de los Sauces area, Neuquén Province, Argentina. The remains include a braincase, cervical, dorsal, sacral and caudal vertebrae, and numerous appendicular bones. It is characterized by the following association of autapomorphies: basal tubera diverge 70 degrees from each other; thin and concave lamina that unit basal tubera ventrally, basioccipital condyle wider than the proximal portion of the basal tubera; posterior dorsal neural spines with large prespinal lamina reinforced by two small accessory laminae, distai end of pubic blade rectangular and medially thick. A cladistic phylogenetic analysis placed Muyelensaurus pecheni gen. et sp.nov. and Rinconsaurus caudamirus in a new eutitanosaur clade named herein Rinconsauria. This new clade include middle-sized sauropods different from Aeolosaurini, Opisthocoelicaudiinae or Saltasaurinae taxa. Key words: Sauropoda. Titanosauria. Rinconsauria. Muyelensaurus pecheni gen. et. sp.nov. Late Cretaceous. RESUMEN: Un nuevo saurópodo Titanosaurio dei Cretácico superior de Neuquén, Patagônia, Argentina. El descubrimiento de Muyelensaurus pecheni gen. et. sp. nov., un nuevo y esbelto titanosaurio, es relevante tanto desde el punto de vista anatómico como sistemático. Los especimenes proceden de los estratos dei Cretácico superior de la Formación Portezuelo (Turoniano-Coniaciano temprano) de Loma dei Lindero, en la zona de Rincón de los Sauces, Provincia dei Neuquén, Argentina. Los restos incluyen un basicráneo, vértebras cervicales, dorsales, sacras y caudales y numerosos huesos apendiculares. Esta caracterizado por la siguiente asociación de autopomorfias: tubera basal diverge 70 grados una de otra; tubera basal unida ventralmente por una lâmina delgada y côncava; cóndilo basioccipital mas ancho que la porción proximal de la tubera basal; espinas neurales en la vértebras dorsales posteriores con una lâmina preespinal larga y reforzada por dos pequenas lâminas accesorias; extremo distai de la lâmina púbica de forma rectangular y gruesa medialmente. El análisis filogenético cladístico ubica a Muyelensaurus pecheni gen. et sp. nov. y a Rinconsaurus caudamirus en un nuevo ciado de Eutitanosaurio que denominamos aqui como Rinconsauria. Este ciado incluye a saurópdos de mediano tamano diferentes de otros taxa de Aeolosaurini, Opisthocoelicaudiinae o Saltasaurinae. Palabras clave: Sauropoda. Titanosauria. Rinconsauria. Muyelensaurus pecheni gen. et. sp.nov. Cretácico Superior. INTRODUCTION and appendicular bones is relevant from anatomical and systematic viewpoints. Titanosauria is the most diverse and geographically In Argentina, only the titanosaurids Antarctosaurus widespread Cretaceous sauropod clade. In spite wichmannianus (Huene, 1929), Saltasaurus loricatus of that, most of titanosaurs are represented by (Bonaparte & Powell, 1980), Bonitasaura salgadoi incomplete skeletal elements lacking well- (Apesteguía, 2004), Bonatitan reigi (Martinelu & Forasiepi, preserved cranial remains. In this context, the 2004), and an unnamed specimen from Bajo de Anelo, discovery of a new genus and species represented Neuquén Province (Calvo & Kellner, 2006) include by a braincase associated with numerous axial descriptions of braincase. In contrast, well-preserved 1 Submitted on September 14, 2006. Accepted on October 10, 2007. 2 Universidad Nacional dei Comahue, Centro Paleontológico Lago Barreales, Avenida Megaraptor 1450. Ruta Prov. 51, km 65. Neuquén. Argentina. * Corresponding author, e-mail: [email protected]. ar. 3 Laboratorio de Paleovertebrados, IANIGLA-CONICET, Instituto Argentino de Nivología, Glaciología y Ciências Ambientales, Centro Regional de Investigaciones Científicas y Tecnológicas, Avda. Ruiz Leal s/n, Parque Gral. San Martin (5500) Mendoza, Argentina. E-mail: [email protected]. ICB, Universidad Nacional de Cuyo. Centro Universitário, Parque Gral. San Martin (5500), Mendoza, Argentina. 486 J.O.CALVO, B J.GONZÁLEZ-RIGA & J.D.PORFIRI titanosaurids recently recovered in Patagônia that named Pehuenchesuchus enderí (Turner & Calvo, include cranial remains (Calvo et al, 1997; Coria & 2005) were found in strata tentatively assigned to Salgado, 1998) have not been described yet. Rio Neuquén Subgroup (Late Turonian-Coniacian). In Northwestern Patagônia, the Neuquén Group is In Loma dei Lindero site, 10km West to Rincón de the richest dinosaur bearing unit. It comprises a los Sauces Town, numerous sauropod bones were thick continental succession (maximum thickness collected in fluvial fácies assigned to the Portezuelo l,300m) deposited between Early Cenomanian to Formation, base of the Rio Neuquén Subgroup (Late Early Campanian (Leanza & Hugo, 2001). The Turonian-Early Coniacian after Leanza & Hugo, Neuquén Group has given since 1882 numerous 2001). The fossils come from reddish pelites and titanosaur species (Huene, 1929; Powell, 1986; yellowish sandstones of overbank fácies. A partially Calvo & Bonaparte, 1991; Bonaparte & Coria, 1993; similar sedimentary context is also present in Cerro González Riga, 2003; 2005). Guillermo area (Mendoza Province) (González Riga In the last years, extraordinaiy titanosaur fossils were & Astini, 2007), where the titanosaur Mendozasaurus found in Rincón de los Sauces area, Northern Neuquén neguyelap was found (González Riga, 2003; 2005). Province, Patagônia. Rinconsaums caudamirus (Calvo Institutional abbreviation - FMNH PR, Field Museum & González Riga, 2003) is the first species described of Natural History, Chicago, USA; MRS-Pv, Museo from this locality. Moreover, other discoveries carried de Rincón de los Sauces, Neuquén, Argentina; out in Rincón de los Sauces include articulated MUCPv. Museo de Paleontologia de la Universidad specimens that have not been described yet (Calvo et Nacional dei Comahue, Neuquén, Argentina. al, 1997; Coria & Salgado, 1998). The objective of this work is to describe a new and slender titanosaur from the Late Cretaceous, and to analyze their phylogenetic relationships. The study of this taxon, the second species described in Rincón de los Sauces, is a new evidence of the morphologic diversity of the South American titanosaurs. MATERIAL AND METHODS The fossils had been found at Loma dei Lindero site, 10km west to Rincón de los Sauces Town (Fig. 1). This site was excavated during four years (1998-2001) under the direction of the first author (J.O.C.). The first fóssil remains from Loma dei Lindero site were found by Marcelino Palomo and communicated to authors by Salvador Palomo in 1997. At Loma dei Lindero locality, numerous titanosaur remains (~ 300 bones) associated with a turtle specimen and theropods have been found (Calvo & González Riga, 1999; de la Fuente et al, 2007). Fóssil remains are housed at the Laboratory of Rincón de los Sauces Museum. Geological Setting In the last years, well-preserved titanosaur sauropods were found in Rincón de los Sauces area, Northern Neuquén Province, Patagônia. In the Rio Seco site, located 2km South to Rincón de los Sauces Town, a slender eutitanosaur named Fig. 1- Map of Neuquén basin (Patagônia, Argentina) showing Rinconsaurus caudamirus (Calvo & González Riga, the locality where the holotype of Muyelensaums pecheni 2003) and a basal sebecosuchian crocodyliform gen. et sp.nov. was found. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 A NEW TITANOS AUR SAUROPOD FROM THE LATE CRETACEOUS OF NEUQUÉN, PATAGÔNIA, ARGENTINA 487 SYSTEMATIC PALEONTOLOGY Muyelensaurus pecheni sp.nov. Etymology - In honor of Dra. Ana Maria Pechen, SAURISCHIA Seeley, 1887 Main head of the National University of Comahue SAUROPODA Marsh, 1878 (2002-2006), who supported the study of dinosaur TITANOSAURIA Bonaparte & Coria, 1993 fossils in Neuquén Province, Patagônia. TITANOSAURIDAE Lydekker, 1893 RINCONSAURIA new taxon Holotype - MRS-PV 207, a braincase including partial frontal and parietal, basioccipital, incomplete Etymology - In reference to Rincón de los Sauces basipterigoid process, supraoccipital, exoccipital, area, Neuquén Province, Patagônia, Argentina. basisphenoidals tubers, orbitosphenoids, and Definition - Muyelensaums, Rinconsaurus, their incomplete parasphenoids. most recent common ancestor and all of its Paratype - The following bones associated with descendants. the holotype are included: represented by a Diagnosis - Titanosaurids with the following premaxilar (MRS-Pv 59, 60, 337), cervical association of characters: suboval teeth with labial vertebrae (MRS-Pv 65, 66,121, 122, 204, 230, 232, and lingual faces well differentiated by crests, bony 229, 279, 391, 392, 420, 422, 428), dorsal processes that support the postzygapophyseal vertebrae (MRS-Pv 67, 68, 224, 404, 412, 421), facets in middle caudal vertebrae, and posterior sacrum (MRS-Pv 355), caudal vertebrae (MRS-Pv caudal centra depressed posteriorly. 135, 137, 164,170, 171, 173, 174, 189, 190, 193, 200, 209, 214, 252, 377, 408), scapula (MRS-Pv Included species - Rinconsaurus caudamirus Calvo 396, 397, 259), sternal plate (MRS-Pv 125), & González Riga, 2003, and Muyelensauruspecheni humerus (MRS-Pv 70, 132, 212, 352, 357, 387), gen. et sp.nov. ulnae (MRS-Pv 72, 243, 353, 182), radio (MRS-Pv 71, 139) metacarpals (MRS-Pv 127, 152, 157, 181, Muyelensaurus gen.nov. 198, 231, 235, 236), ischia (MRS-Pv 87, 199, 247, 251), ilia (MRS-Pv 131, 134, 202, 399), pubes Etymology - From Muyelen, one of the names of (MRS-Pv 88, 154, 204, 371), femora (MRS-Pv 89, the Colorado river after the Mapuche indigenous 91, 352, 356, 358, 389, 429), tibiae (MRS-Pv 161, language (Erize, 1988); saurus (Greek), lizard. 162, 257, 266), fibulae (MRS-Pv 90, 245, 246, 258, Type-species - Muyelensaurus pecheni sp.nov. 271, 369, 375), astragalus (MRS-Pv 187), metatarsals (MRS-Pv 50-54, 128, 141, 142, 166, Diagnosis - Slender Rinconsauria characterized by 168, 242, 273, 274, 378, 379), and phalanges the following association of autapomorphies: basal (MRS-Pv 55, 56, 57, 58, 143, 144-147, 165, 237). tubera diverge 70 degree from each other; extensive, thin and concave medial lamina that unit basal Referred material - posterior dorsal vertebrae (MRS- tubera ventrally, basioccipital condyle wider than Pv 123, 203, 419 and 431). the proximal portion of the basal tubera; posterior Specimens - The holotype and paratypes of dorsal neural spines with large prespinal lamina Muyelensaurus pecheni sp.nov. correspond to four reinforced by two small accessory laminae, distai adult and one juvenile individuais. All fóssil end of pubic blade rectangular and medially thick. remains were found disarticulated but associated In contrast to Rinconsaurus, Muyelensaurus in the same site and include cranial remains, gen.nov has anterior dorsais with neural spines cervical, dorsal, sacral, and caudal vertebrae, and posteriorly directed less than 45 degree with respect appendicular bones (Fig.2). Duplicate bones to the vertical, posterior dorsais with large and deep represented by appendicular bones exhibit the infradiapophyseal fossa and ventral face of same morphological characters. This evidences the posterior cervical centra narrow and strongly presence of a monospecific assemblage. concave at levei of the parapophysis. Moreover, different from Rinconsaurus, Muyelensurus gen.nov. Horizon, age and locality: Portezuelo Formation, lacks an accessory centroparapophyseal lamina in Rio Neuquén Subgroup, Neuquén Group, Late posterior dorsais, anterior caudais with Cretaceous, Late Turonian-Early Coniacian (after postzygapophyseal process, and amphicoelous- Leanza & Hugo, 2001). The fossils come from Loma biconvex or amphicoelous-opisthocoelous-biconvex dei Lindero site, 10km West to Rincón de los Sauces caudal centra. City, Neuquén Province, Patagônia, Argentina. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 488 J.O.CALVO, BJ.GONZÁLEZ-RIGA& J.D.PORFIRI Fig.2- Muyelensaumspecheni gen. et sp.nov., preserved bones (in black) shown in a titanosaur skeletal reconstruction of Lehman & Coulson (2002). DESCRI PTION Skull - Premaxilar fragments with teeth (Fig.3), and an incomplete braincase (Fig.4) were recovered. Suboval teeth are characterized by the presence of labial and lingual faces well differentiated by crests, like in Rinconsaums caudamims (Calvo & González Riga, 2003). The braincase is slightly crushed. It preserves a fragment of the left parietal and frontal, a fragment parietal, complete supraoccipital, the right paraoccipital process, basioccipital condyle, basal tubera, a fragment of the rigth basipterygoid process, and partially preserved orbitosphenoid, crista prootica, and parasphenoid. The frontal, represented by a small fragment, forms the posterior rim of the orbit. In anterior view, it is fused to the orbitosphenoid. The parietal is robust and axially elongated. The supratemporal fenestrae are relatively reduced, transversely orientated and laterally directed, as in the titanosaur Saltasaums and some other sauropods (Wilson & Sereno, 1998; Curry Rogers & Forster, 2001). The preserved medial border of the supratemporal fenestra is formed by the parietal. On the anterior rim of the supratemporal fenestra participates the frontal, like in Rapetosaurus (Curry Rogers & Forster, 2004), Nemegtosaurus Fig.3- Muyelensauruspecheni gen. et sp.nov., a fragment of and Saltasaurus (contra Wilson, 2002), and premaxilar with teeth (MRS-Pv 59) in lateral view. Scale Bonatitan (Martinelli & Forasiepi, 2004). bar = lcm. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 A NEW TITANOS AUR SAUROPOD FROM THE LATE CRETACEOUS OF NEUQUÉN, PATAGÔNIA, ARGENTINA 489 A B Fig.4- Muyelensaums pecheni gen. et sp.nov., braincase (MRS-Pv 207) in occipital view (A, picture; B, drawing). (Bo) basioccipital, (Bt), basitubera, (Fm), foramen magnum, (Ml), medial lamina, (So) supraoccipital. Scale bar = 2cm. The proximal portion of the supraoccipital has a Cervical vertebrae - An almost complete middle subquadrangular shape. In spite of that the distai cervical vertebra and numerous incomplete end is not preserved. There is a small process that remains were collected (Fig.5; MRS-Pv 65). This shows that it was directed ventrally as in cervical has an opisthocoelous centrum as wide Saltasaurus. as high in posterior view and relatively long (ratio: total length / height of cotyle more than The basioccipital is slightly deformed by compression. 4.0). In contrast to Rinconsaurus caudannirus In posteroventral view, it is subtriangular with its (Calvo & González Riga, 2003), the lateral faces dorsal border slightly concave and their lateroventral have a deep concavity, but lack a true sides convex. The neck is constricted transversely pleurocoels. The posterior centrodiapophyseal and concave anteroposteriorly; therefore, the condyle and postzygodiapophyseal laminae are well has a mushroom shape, an unusual morphology defined, as in other titanosaurs like among sauropods. Rapetosaurus krausei (Curry Rogers & Forster, The basisphenoid is formed by the tubera and the 2001). The neural spine is formed by the fusion of basipterygoid processes. The first ones are complete spinoprezygapophyseal and spinopostzygapophyseal but the second ones are missing except by the laminae. It has a triangular contour in lateral proximal portion of the right process. Basal tubera view and is thinner distally than those of are well separated by an extended and thin medial titanosaur specimen “Series A” from Peirópolis, lamina (see Ml in Fig.4) that has a concave ventral Brazil (Powell, 1987). Prezygapohysis process contour in a posterior view. Basal tubera diverge surpasses the anterior border of the centrum, but 70 degree from each other (Fig.4). A lateral ridge in contrast to Rinconsaurus, the postzygapophyses connects each basal tubera with the condylar neck do not extend beyond the posterior border. The on its externai side; and a small ridge unites each prezygapophyseal facets are slightly oriented tubera with the midline. In between these ridges, dorsomedially. The diapophysis is reinforced by a wide depression is developed opened only on the the posterior centrodiapophyseal, pre2ygodiapophyseal ventral side. The proximal portion of the right and postzygodiapophyseal laminae. Likewise basipterygoid process is preserved. According to some titanosaurs (Saltasaurus, Rapetosaurus), the evidence they are well separated and were these laminae form a supradiapophyseal concavity directed almost parallel. lacking well-defined borders (González Riga, 2005). Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 490 J.O.CALVO, B J.GONZÁLEZ-RIGA & J.D.PORFIRI have been recovered (MRS-Pv 204, 230, 232, and 66). Anterior dorsal vertebra - One complete anterior dorsal vertebra have been recovered (Fig.6; MRS-Pv 404). The neural arch is three times higher than the centrum and is placed anteriorly. The centrum has a deep pleurocoel that occupies the half of the length. The parapophysis is placed on the top of the centrum. The prezygapophysis are wide and have an oval shape. They are well separated from the midline. The centroprezygapohyseal and diapopre zygapophyseal lamina are robust. The diapophysis is connected to the neural spine by a robust spinodiapophyseal lamina. Ventrally, the diapophysis is Fig.5- Muyelensaurus pecheni gen. et sp.nov., middle cervical vertebra reinforced by a paradiapophyseal lamina (MRS-Pv 65) in lateral view. Scale bar = 5cm. and a centrodiapophyseal lamina. In contrast to this taxon, the centropre The parapophyses, located in the anterior half of zygapophyseal laminae are absent in Rinconsaurus. the vertebral body, are laminar and subtriangular Small accessoiy centrodiapophyseal laminae are born in shape. In contrast to Rinconsaurus, the ventral on the base of the diapoparapophyseal laminae and face is narrow and strongly concave at levei of the are connected to the centrodiapophyseal laminae. parapophysis. Other cervicais (MRS-Pv 121, 391, Therefore two deep depressions are developed below 392, 420, 422, 229, 428, and 279) are crusted and the diapophysis. In posterior view a centro damaged, but have a similar size to the cervical postzygapophyseal lamina is present. The single vertebra described. In contrast, one cervical (MRS- neural spine is directed posteriorly around 45 degree Pv 122) is assigned to a larger specimen (centrum with respect to the vertical, in contrast to length: 43cm). It shows a tall neural spine that Rinconsaurus that reaches 60 degree. The prespinal have a subtriangular contour in lateral view. Other lamina is present and transverse processes are cervicais of large size, but fragmentary preserved, directed dorsolaterally. Fig.6- Muyelensaurus pecheni gen. et sp.nov., anterior dorsal vertebra (MRS-Pv 404) in anterior (A), lateral (B), and posterior (C) views. Scale bar = 5cm. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 A NEW TITANOSAUR SAUROPOD FROM THE LATE CRETACEOUS OF NEUQUÉN, PATAGÔNIA, ARGENTINA 491 Posterior dorsal vertebrae - Several disarticulated lateral faces of the centrum (Fig.8A) show deep posterior dorsal vertebrae (MRS-Pv 67, 68, 412, eye-shaped pleurocoels with acuminate and 224) and incomplete posterior dorsal arch posterior contour, a synapomorphy of (MRS-Pv 421) were preserved. The posterior Titanosauria (sensu Salgado et al, 1997a). They lack dorsais have opisthocoelous and subcircular hyposphene-hypantrum articulations. Post centra, as wide as high (Fig.7). The lateral and zygapophyseal facets are elongated, narrow, ventral faces are anteroposteriorly concave. The relativelly small and directed ventromedially (Fig.8B). Fig.7- Muyelensauruspecheni gen. et sp.nov., stereophotographs of the posterior dorsal vertebra (MRS-Pv 412) in anterior view. Scale bar = 5cm. Fig.8- Muyelensaurus pecheni gen. et sp.nov., posterior dorsal vertebra (MRS-Pv 412) in lateral (B) and posterior (B) views. Scale bar = 5cm. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 492 J.O.CALVO, B J.GONZÁLEZ-RIGA & J.D.PORFIRI They are connected to the centropostzygapophyseal have been collected (MRS-Pv 355). They are fused laminae. In contrast to Rinconsaums caudamirus and have neural spines United each other by an (MRS-Pv 17, 18), the most posterior dorsais lack interspinal medial lamina. The sacral ribs are postzygodiapophyseal lamina. The diapophyses are laminar and dorsally expanded reaching the levei supported by posterior and anterior centro of the neural spines. diapophyseal laminae. These laminae delimit a Caudal vertebrae - Numerous caudal vertebrae subtriangular infradiapophyseal depression in corresponding to several individuais of different some dorsais (MRS-Pv 67 and 68) and a true sizes were recovered. All caudais have strongly infradiapophyseal fossa in the dorsal MRS-Pv 412. procoelous centra, in contrast to Rinconsaurus that A less developed infradiapophyseal depression is is characterized by the intercalation of present in posterior dorsal of Rinconsaurus amphicoelous-biconvex or amphicoelous- caudamirus (MRS-Pv 13). The prespinal lamina is opisthocoelous-biconvex centra. large anteroposteriorly and reaches the base of the neural arch. There are two small accessory The most anterior caudal recovered (Fig.9; MRS- prespinal laminae bifurcated close to the base of Pv 200) is large and have a centrum slightly inclined the neural arch (Fig.7). This character has not been anteriorly less than Gondwanatitan (Kellner & described in any other posterior dorsal vertebrae Azevedo, 1999) and Aeolosaurus Powell, 1986. The of titanosaurs and is considered herein as a anterior face of the centrum is as wide as high. probable autapomorphy of Muyelensaurus. In The neural arch is located over the anterior border Mendozasaurus, anterior dorsais have a similar of the centrum, like Aeolosaurini species. The structure but they are small spinoprezy neural spine is ticker distally, and has a gapophyseal laminae that are directed to the quadrangular contour in dorsal view. It is prezygapophysis (González Riga, 2003). Other supported by the prespinal and postspinal laminae. peculiar character of the dorsais is the presence of accessory spinodiapophyseal lamina. This lamina exhibits a variable morphology: it is extensive in some dorsais (MRS-Pv 67 and 68) whereas it is reduced or absent in other dorsais. Accessory spinodiapophyseal laminae, but with less development, are also present in Argentinosaurus huinculensis (Bonaparte & Coria, 1993). The neural canal is reduced and shows a subtriangular contour. Over the neural canal, there is a deep fossa divided by a medial septum. The neural spines are less posteriorly directed toward the posterior section of the series. The neural spines have lanceolate anterior and posterior contours due to the development of lateral process of the spinodiapophyseal lamina. Other middle and posterior dorsal vertebrae recovered are distorted and considered as refereed material (MRS-Pv 123, 203, 419, and 431). They exhibit a large and very deep infradiapophyseal fossa limited by the anterior and posterior centrodiapophyseal laminae. Finally, in contrast to Muyelensaurus, the posterior dorsal vertebrae of Rinconsaurus have an accessory centroparapophyseal lamina, which is extended from the base of the parapophysis to the base of centrodiapophyseal lamina (MRS-Pv 17 and 18). This structure is absent in other titanosaurs and can be interpreted as an autapomorphy of Rinconsaurus. Fig.9- Muyelensauruspecheni gen. et sp.nov., anterior caudal Sacrum - Five sacral vertebrae partially preserved vertebra (MRS-Pv 200) in lateral view. Scale bar = 5cm. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 A NEW TITANOS AUR SAUROPOD FROM THE LATE CRETACEOUS OF NEUQUÉN, PATAGÔNIA, ARGENTINA 493 In Rinconsaurus the neural spines of the anterior process that is present in Rinconsaurus. In caudais are less thick than they are distally. The contrast, middle and middle-posterior caudais partially preserved transverse processes are wide (MRS-Pv 193, 164, and 135) share with and posteriorly directed. The characteristic Rinconsaurus the presence of a postzygapophyseal process of the postzygapophyseal facets, present process (Figs. 10-11). The neural spines are in Rinconsaurus caudamirus (MRS-Pv 23), is incomplete, but the preserved portion indicates absent in Muyelensaurus. an elongate morphology axially extended, and posterior caudal centra are depressed posteriorly. Other anterior and middle caudal vertebrae The distai caudais (MRS-Pv 170, 171, 190, 189, correspond to a middle-sized specimen (MRS-Pv and 209) are similar to those of Rinconsaurus. 377, 137, 174, 408, 214, 252, and 173) or to a They have very reduced neural spines slightly juvenile specimen (MRS-Pv 164 and 193). In inclined anteriorly that become horizontal toward anterior caudais (MRS-Pv 137) the centra are the distai end of the tail. In contrast to slightly inclined anteriorly, but this character Rinconsaurus, the neural arch of the distai caudal disappears toward the middle section of the tail. are reduced anteroposteriorly since they never All anterior caudais lack the postzygapophyseal reach the half of the centrum length. Fig.10- Muyelensauruspechenigen. et sp.nov., middle caudal vertebra (MRS-Pv 164) in anterior (A), lateral (B) and dorsal (C) views. Scale bar = 2cm. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007 494 J.O.CALVO, B.J.GONZÁLEZ-RIGA& J.D.PORFIRI Appendicular bones - The abundant bones recovered are similar to those of Rinconsaurus and other titanosaurs, but show some differences. They will be described in detail elsewhere. The sternal plate (MRS-Pv 125) exhibits a typical semilunar contour, and its posterior border is not straight as that present in some titanosaurs, like Mendozasaurus and Malawisaurus (González Riga, 2003). A complete right scapula (Fig. 12.A; MRS-Pv 259) and two partial scapular blades (MRS-Pv 396 and 397) were recovered. The scapula, a long and laminar bone, has a thin and slender scapular blade. The distai end is expanded, the diagonal acromion is thin and the supracoracoideus fossa is veiy prominent. The ventral border is slightly concave up to its union with the proximal end, where begins a new concave border. Six humeri were collected (MRS-Pv 70, 132, 212, 352, 357, and 387). One left humerus (Fig.l2B; MRS-Pv 70) is the best preserved. It is relatively slender, since the proximal width Fig.ll- Muyelensaums pecheni gen. et sp.nov., posterior caudal vertebra (MRS-Pv 135) in lateral view. Scale bar = 2cm. reaches the 25 percent of the total length. Fig. 12- Muyelensaums pecheni gen. et sp.nov., right scapula (MRS-Pv 259) in lateral view (A), left humerus (MRS-Pv-70) in anterior view (B). Scale bar = lOcm. Arq. Mus. Nac., Rio de Janeiro, v.65, n.4, p.485-504, out./dez.2007