Abstract: In the last two decades, the number of phylogenetically informative anatomical characters recognized in the appendicular skeleton of titanosaurian sauropod dinosaurs has increased dramatically with the discovery of new and comparatively complete specimens. Here we provide an overview of the appendicular skeletal morphology of South American titanosaurs and discuss its significance for phylogenetic reconstruction. The appendicular skeletal diversity of South American titanosaurs is substantially greater than was initially appreciated. Moreover, some regions of the appendicular skeleton, such as the pes, exhibit remarkable variability in form. Multiple synapomorphies of Titanosauria and the less inclusive clades Lithostrotia and Saltasauridae consist of characters of the girdles and limbs. Although the phylogenetic definitions of titanosaurian clades such as Saltasaurinae and Lognkosauria are stable, the taxonomic content of these clades has varied in recent analyses depending on the phylogenetic topology recovered. Within Titanosauria, the results of four recent, largely independent analyses support the existence of a derived titanosaurian lineage distinct from the ‘Saltasaurinae line,’ which is herein termed Colossosauria. At present, this clade is mainly comprised by taxa within Lognkosauria and Rinconsauria, and is useful in discussions of titanosaurian lower-level relationships.

Abstract We describe a dentary of a new titanosaur sauropod, Baalsaurus mansillai, gen. et sp. nov. from the Late Cretaceous of Patagonia, Argentina. The material comes from the Portezuelo Formation, Neuquén Group. Titanosaur sauropods lower jaws are scarce and only nine taxa with dentaries have been described. There are two types of morphology in titanosaur dentaries; “L” shaped or “U” shaped based on the shape, without a phylogenetic issue. In this paper; we recognize a new taxa, Baalsaurus mansillai, represented by an “L” shaped dentary with three apomorphic characters that are not present in other taxa: dentary alveoli with 10 teeth in the anterior ramus, a ventrally and anteriorly inclined symphysis and a wide ventral Meckelian groove surrounded by a thin lamina that forms a keel on the ventral border of the dentary.

Rests of Aeolosaurus colhuehuapensis, a titanosaur from the Colhué Huapi lake, in the southern Chubut Province, Argentina, were analyzed. The materials under study include twenty one caudal vertebrae and seven haemal arches. They were recovered articulated in overbankfacies related to deposits of multi-channel fluvial systems of high sinuosity in the informally called "strata of the Colhué Huapi lake" of Campanian-Maastricthian age. These systems displayed important seasonal fluctuations in the paleodischarge and they were encompassed in a semi-arid climate. The taphonomic history was inferred from the analysis of several taphonomic characteristics present in the bones and macro- and microscopic sedimentologic observations. The presence of tenuous longitudinal striation, the absence of bone exfoliation, the articulate condition of the materials and the dorsal bow of the caudal series, support a short period of subaerial exposure with a rapid burial episode. The absence of abrasion marks in the materials indicates that they had scarce or null transport; therefore, they could be considered as autochthonous. The dorsal bow of the tail shows an opisthotonus posture, also exhibited by some theropod and sauropod dinosaurs, but undocumented in the Chubut Group. The recent fluctuant climatic conditions, with variations of extreme humidity and drought, strongly affected the preservation of the materials. The present work is the first detailed taphonomic study of a dinosaur preserved in proximal floodplain facies for the Chubut Group. Finally, the preservation of sauropod bones in those facies is relevant because this type of sub-environment possess a high rate of sediment input as well as scarce or null re-working of the skeletal remains, which favor the conservation of articulated skeletal elements. These findings are very important for the taphonomic andphylogenetic analysis of the titanosaur clade, in which the majority of the taxa are represented by isolated and unarticulated remains.

Los restos de un Aeolosaurus colhuehuapensis, un titanosaurio procedente del lago Colhué Huapi, en el sur de Chubut, Argentina, fueron analizados. Los materiales estudiados incluyen veintiún vértebras caudales y siete hemapófisis, y se hallaron articulados en facies correspondientes a depósitos de desbordamientos vinculados a sistemas fluviales multicanalizados y de alta sinuosidad presentes en los aquí denominados "estratos del lago Colhué Huapi" de edad Campaniano-Maastrichtiano. Estos sistemas poseían importantes fluctuaciones estacionales en la paleodescarga y estaban enmarcados en un clima semiárido. La historia tafonómica fue inferida a partir del análisis de diversas características presentes en los restos estudiados y de observaciones sedimentológicas macro y microscópicas. La presencia tenue de estriamiento longitudinal, la escasa exfoliación, el grado de articulación y el arqueamiento dorsal de la serie caudal, sugieren un corto tiempo de exposición subaérea y rápido sepultamiento. La falta de marcas de abrasión en los elementos conservados indica escaso o nulo transporte, por lo que los restos podrían ser considerados autóctonos. El curvamiento dorsal de la cola muestra un arqueamiento opistótono, también presente en algunos terópodos y saurópodos, pero aun no documentado en el Grupo Chubut. Las condiciones climáticas actuales, con variaciones de extrema humedad y sequía, afectaron marcadamente los elementos fósiles preservados. El presente trabajo constituye el primer caso de estudio tafonómico en detalle de un dinosaurio preservado en facies de planicie de inundación proximal para el Grupo Chubut. Finalmente, el hallazgo de saurópodos en estas facies es relevante, dado que este tipo de subambiente posee una alta tasa de aporte sedimentario y reducido a nulo retrabajo de los restos óseos, favoreciendo la preservación de elementos esqueletales articulados. Esto es de suma importancia para el análisis taxonómico y filogenético del ciado de los titanosaurios, en el cual la mayoría de los taxones están representados por restos desarticulados y aislados.

Estimativas de velocidade a partir de trilhas de Titanopodus mendozensis González Riga e Calvo fornecem informações a respeito da locomoção de saurópodes titanossaurianos que viveram na América do Sul durante o Cretáceo Superior.Icnitos de Titanopodus foram encontrados em Agua del Choique, sendo este um sítio de pegadas recentemente descoberto na Formação Loncoche, Campaniano Superior-Maastrichiano Inferior de Mendonza, Argentina. Este estudo de velocidade segue a hipótese de similaridade dinâmica proposta por Alexander. Como um refinamento deste método, uma equação complementar é aqui apresentada tomando como base um espécime titanossauriano articulado coletado em estratos que são tidos como correlativos àqueles que forneceram as pegadas de Titanopodus (Formação Allen, Bacia Neuquén). Esta análise indica que a altura da bacia pode ser estimada como tendo 4,586 vezes o comprimento da pegada do pé em titanossauros derivados. A velocidade é calculada com uma estimativa da altura da bacia e as medidas da passada. O estudo de duas trilhas de medidas amplas indica que os icnitos de Titanopodus foram produzidos por titanossauros de tamanho mediano (altura da bacia de 211-229 cm) que caminhavam a 4,7-4,9 km/hem direção ao sul e sudeste, seguindo, em parte, um caminho sinuoso. Estas velocidades e algumas características tafonômicas das pegadas (margens proeminentes, formatos alongados distorcidos) apontam para a capacidade de titanossauros derivados de caminhar efetivamente sobre um substrato muito úmido e escorregadio. No registro icnológico, as velocidades de caminhada dos geradores de Titanopodus são um pouco mais rápidas do que aquelas previamente inferidas para a maioriados saurópodes.

Speed estimations from trackways of Titanopodus mendozensis González Riga and Calvo provide information about the locomotion of titanosaurian sauropods that lived in South America during the Late Cretaceous. Titanopodus ichnites were found at Agua del Choique, a newly discovered track site in the Loncoche Formation, Late Campanian-Early Maastrichtian of Mendoza, Argentina. This speed study follows the hypothesis of dynamic similarity proposed by Alexander. As a refinement of this method, a complementary equation is presented here based on an articulated titanosaurian specimen collected in strata that are regarded as correlative to those that have yielded Titanopodus tracks (Allen Formation, Neuquén Basin). This analysis indicates that hip height can be estimated as 4.586 times the length of the pes track in derived titanosaurs. With an estimation of the hip height and the stride measurements, the speed is calculated. The study of two wide-gauge trackways indicates that Titanopodus ichnites were produced by mediumsized titanosaurs (hip height of 211-229 cm) that walked at 4.7-4.9 km/h towards the south and southwest, following, in part, a sinuous pathway. These speeds and some taphonomic features of tracks (prominent rims, distorted elongated shapes)indicate the capacity of derived titanosaurs for walking effectively over a very wet and slippery substrate. In the ichnological record, the walking speeds of Titanopodustrackmakers are somewhat faster than those previously inferred for most sauropods.

We describe new fossil vertebrates from the Loncoche Formation in the Calmu-Co area of Mendoza Province, Argentina. At this site the lower section of the formation corresponds to lacustrine and meandering fluvial environments (facies associations A and B, respectively), whereas the middle levels of the formation are assigned to marginal marine deposits (facies association C). The vertebrates were found in facies association C and include fishes (i.e., Chondrichthyes, Teleostei, Lepisosteidae and Dipnoi), Chelidae turtles (cf. Yaminuechelys, cf. Prochelidella), dinosaurs (Titanosauria) and plesiosaurs (Elasmosauridae). The remains, found in clastic and calcareous facies (mudstones and grainstones), are interpreted to reflect channel and deltaic plain environments. The diverse ecology (terrestrial, fresh water, marine) and the fragmentary character of these skeletal concentrations suggest mixing of fossil remains from littoral environments and fluvial systems. Our findings indicate that the Atlantic marine ingression that covered northern Patagonia reached Calmu-Co, in the western part of the Neuquén basin. Vertebrates from Calmu-Co area are assigned to the late Campanian-early Maastrichtian on the basis of similarities with vertebrates assemblages found in other sites within Mendoza (Ranquil-Có) and northern Patagonia (Río Negro and Chubut provinces, Allen, La Colonia and Los Alamitos formations).

Se dan a conocer nuevos vertebrados fósiles procedentes de la Formación Loncoche aflorante en el área de Calmu-Co, provincia de Mendoza, Argentina. En esta localidad los niveles inferiores de la formación corresponden a ambientes lacustres y fluviales meandriformes (asociaciones de facies A y B, respectivamente) mientras que los niveles suprayacentes se asignan a depósitos marino-marginales (asociación de facies C). Los vertebrados, procedentes de la asociación de facies C, comprenden peces (por ej. Chondrichthyes, Teleostei, Lepisosteidae y Dipnoi) tortugas Chelidae (cf. Yaminuechelys, cf. Prochelidella), dinosaurios (Titanosauria) y plesiosaurios (Elasmosauridae). Provienen de facies clásticas y calcáreas (mudstones y grainstones) asignadas a canales y planicie deltaica. El carácter fragmentario de estas concentraciones esqueletales constituidas por taxa de requerimientos ecológicos diversos (terrestres, dulceacuícolas y marinos), sugiere la mezcla de restos de ambientes litorales con los provenientes de sistemas fluviales. Estas evidencias indican que la ingresión marina procedente del Atlántico que cubrió el norte de Patagonia, se extendió hasta Calmu-Co, área occidental de la Cuenca Neuquina. Los vertebrados de Calmu-Co se asignan al Campaniano tardío-Maastrichtiano temprano en base a similitudes con asociaciones de vertebrados halladas en otros sitios de Mendoza (Ranquil-Có) y norte de Patagonia (provincias de Río Negro y Chubut, formaciones Allen, La Colonia y Los Alamitos).

This paper deals with the first mammal remains found in the Mariño Formation outcropping in the Divisadero Largo area, Mendoza, Argentina. The Cenozoic levels in this zone are well known by the faunal assemblage of the Divisadero Largo Formation, which allowed the establishment of the Divisaderan Land Mammal Age (Late Eocene-Early Oligocene), but until now no vertebrate fossils had been described from the overlying Mariño Formation (Miocene). This formation also outcrops in the localities of Potrerillos and Cacheuta, Southwest Mendoza city, where some paleobotanical remains and ichnites have been recently found. The specimen studied in this paper is the first accurate datum of fossil mammals from the Mariño Formation, and it could probably constitutes a new taxon for Argentina within the notoungulates Mesotheriidae Mesotheriinae. The specimen consists of a maxillary fragment with right M3 and, separated from the maxillary, the almost complete M2, a labial fragment of M1, the P4 and a P3 fragment. These teeth belong to an adult individual and are characterized by their small size, clearly lesser than that of known Miocene genera Eutypotherium , Typotheriopsis , and Pseudotypotherium . This material presents size similarities with the genus Microtypotherium from Bolivia and the very recently described species from the Chucal Formation (Chile).

Se dan a conocer los primeros restos de mamíferos hallados en sedimentitas de la Formación Mariño, aflorantes en el área de Divisadero Largo, provincia de Mendoza, Argentina. Los niveles cenozoicos de esta zona son conocidos por la asociación faunística de la Formación Divisadero Largo, la cual ha permitido establecer la Edad-mamífero Divisaderense (Eoceno superior-Oligoceno inferior). No obstante, hasta el presente hallazgo no se habían registrado fósiles en las sedimentitas de la Formación Mariño suprayacente asignada al Mioceno. Esta formación aflora también en otras localidades situadas al sudoeste de la ciudad de Mendoza (Cacheuta, Potrerillos), donde recientemente se han encontrado algunos restos vegetales e icnitas. El hallazgo del ejemplar estudiado en este trabajo es de gran importancia, tanto por ser el primer dato fehaciente de mamíferos fósiles provenientes de esta formación como por constituir probablemente un taxón nuevo para Argentina, dentro del grupo de los notoungulados Mesotheriidae Mesotheriinae. El ejemplar consta de un resto maxilar derecho con el M3, el M2 casi completo, un fragmento del M1, el P4 y un fragmento del P3. Estos dientes pertenecen a un individuo adulto y se caracterizan por su pequeño tamaño, significativamente menor que el de los géneros miocenos conocidos, Eutypotherium , Typotheriopsis y Pseudotypotherium . Presenta semejanzas de talla con Microtypotherium de Bolivia y las especies descriptas recientemente de la Formación Chucal de Chile.

In South America, most titanosaur species are represented by incomplete skeletal elements lacking well-preserved cervical vertebrae. In this context, the discovery of cervical remains assigned to Mendozasaurus neguyelap González Riga is relevant from a systematic viewpoint. The fossils were found in the paleontological site and assemblage of the holotype, Río Neuquén Subgroup, late Turonian - late Coniacian from Mendoza Province, Argentina. The cervical vertebrae of Mendozasaurus exhibit differences with those of most titanosaurs; however, they share with Isisaurus colberti (Jain and Bandyopadhyay) from Maastrichthian of India the presence of: a) short vertebral centra (ratio: total length/height of cotyle less than 2.5), b) large and deep supradiapophyseal fossa, and c) relatively tall neural spines (ratio: vertebral height / centrum length more than 1.5). The fossils recovered show an autapomorphic character that enlarges the diagnosis of Mendozasaurus : tall, laminar and transversally expanded mid-posterior cervical neural spines that are wider than vertebral centra and ‘fan-like' or ‘subrhomboid' in shape due to lateral expansions and a subrounded dorsal border. The fossil record of titanosaurs shows a notable morphologic diversity in the cervical series. In particular, Mendozasaurus neguyelap and Isisaurus colberti possess tall neural spines associated with the proportionally shortest cervical centra of any titanosaur. This unusual morphology suggests the development of relatively wide, robust and short necks in Late Cretaceous sauropods from Argentina and India.

En América del Sur la mayoría de las especies de titanosaurios están representadas por restos esqueletales incompletos que no tienen preservadas sus vértebras cervicales. En este contexto, el hallazgo de restos cervicales de Mendozasaurus neguyelap González Riga es relevante desde el punto de vista sistemático. Los restos provienen del mismo sitio paleontológico y asociación fósil del holotipo, Subgrupo Río Neuquén, Turoniano tardío - Coniaciano tardío de la provincia de Mendoza, Argentina. Las vértebras cervicales de Mendozasaurus exhiben caracteres novedosos con respecto a las de otros titanosaurios, si bien comparten con Isisaurus colberti (Jain y Bandyopadhyay) del Maastrichthiano de la India la presencia de: 1) centros vertebrales relativamente cortos (relación longitud del centro/altura del cótilo: inferior a 2,5), 2) profunda y amplia fosa supradiapofisial y 3) altas espinas neurales (relación altura vertebral/longitud del centro: mayor a 1,5). Los restos hallados muestran un carácter que amplía la diagnosis de Mendozasaurus : vértebras cervicales medias/posteriores con espinas neurales altas, laminares y transversalmente expandidas (más anchas que los centros) de contorno anterior en "abanico" o sub-romboidal por el desarrollo de expansiones laterales y un extremo dorsal sub-redondeado. El registro fósil de titanosaurios exhibe una notable diversidad morfológica en la serie cervical. En particular Mendozasaurus neguyelap e Isisaurus colberti se encuentran entre los titanosaurios que poseen los centros cervicales proporcionalmente más cortos asociados con altas espinas neurales. Esta inusual morfología evidencia el desarrollo de cuellos relativamente gruesos, robustos y cortos en saurópodos del Cretácico Tardío de Argentina y la India.

Rinconsaurus caudamirus gen. et sp. nov. (Dinosauria, Sauropoda) is a new and slender Titanosauridae. The specimens come from the Upper Cretaceous strata of the Río Neuquén Formation at Rincón de los Sauces, Neuquén Province, Patagonia, Argentina. The remains include 13 articulated caudal vertebrae and disarticulated cranial, cervical, dorsal and appendicular materials. These fossils belong to three individuals, two adults and one juvenile. This new species is characterized by the following association of autapomorphies: (1) neural spines in mid-anterior dorsal vertebrae inclined posteriorly more than 60 degrees with respect to the vertical, (2) middle caudal vertebrae with bony processes that support the articular surfaces of postzygapophyses, and (3) procoelous posterior caudal centra with intercalation of a series of amphicoelous-biconvex or amphicoelous-opisthocoelous-biconvex centra. A cladistic phylogenetic analysis placed Rinconsaurus in the family Titanosauridae. Within Titanosauridae (Rinconsaurus + Aeolosaurus) is considered a sister group of the clade (Opisthocoelicaudia + (Alamosaurus + (Neuquensaurus + Saltasaurus))). Rinconsaurus caudamirus has preserved short articulated posterior caudal series with amphicoelous, opisthocoelous and biconvex centra. This unusual morphology represents the first such occurrence in sauropod dinosaurs. From the systematic point of view, this discovery is important because Titanosauridae were traditionally defined, among other characters, by strongly developed procoelia in their caudal vertebrae

Rinconsaurus caudamirus gen. et sp. nov., un nuevo titanosáurido (Dinosauria, Sauropoda) del Cretácico Tardío de Patagonia, Argentina. Rinconsaurus caudamirus gen et sp. nov. (Dinosauria, Saurpoda) es un nuevo y esbelto Titanosauridae proveniente de la Formación Río Neuquén, Cretácico Superior de Rincón de los Sauces, Provincia de Neuquén, Patagonia, Argentina. Sus restos están integrados por 13 vértebras caudales articuladas y materiales craneales, cervicales, dorsales y apendiculares desarticulados, que pertenecen a tres individuos, dos adultos y un juvenil. Este nuevo taxón se caracteriza por la siguiente asociación de autapomorfías: (1) vértebras dorsales medioanteriores con espinas neurales inclinadas posteriormente más de 60 grados con respecto a la vertical, (2) vértebras caudales medias con procesos óseos que sostienen las carillas articulares de las poszigapófisis y (3) vértebras caudales procélicas con intercalaciones de series con centros anficélicos y bioconvexos, o con centros anficélicos, opistocélicos y biconvexos. Un análisis filogenético cladista permite incluir a Rinconsaurus en la familia Titanosauridae. Dentro de Titanosauridae (Rinconsaurus +Aeolosaurus) es considerado un grupo hermano del clado (Opisthocoelicaudia + (Alamosaurus + (Neuquensaurus + Saltasaurus))). Rinconsaurus caudamirus presenta dos cortas secuencias caudales posteriores articuladas con centros anficélicos, opistocélicos y biconvexos. Esta inusual morfología se registra por primera vez en dinosaurios saurópodos. Es importante desde el punto de vista sistemático, ya que Titanosauridae ha sido tradicionalmente definido, entre otros caracteres, por la presencia de fuerte procelia en sus vértebras caudales