Marianella Talevi, Marta S. Fernández, e Ignacio Cerda

Los mosasaurios fueron un grupo de escamados que habitaron los océanos y mares epicontinentales de todo el mundo durante el Cretácico Tardío. Su registro fósil abarca todos los continentes, incluyendo Antártida. En la cuenca James Ross (Península Antártica) los restos atribuibles a mosasaurios han sido reportados desde hace más de un cuarto de siglo. La mayor parte del material, excepto por el holotipo del tylosaurino Taniwhasaurus antarcticus (Novas, Fernández, Gasparini, Lirio, Nuñez y Puerta, 2002) Martin y Fernández, 2007 corresponde principalmente a dientes y vértebras. Con base en este material se ha podido documentar la presencia de tylosaurinos en el Campaniano tardío (Formación Santa Marta, Isla James Ross), en el Maastrichtiano temprano (Formación Snow Hill Island, Isla Vega), y en el Maastrichtiano tardío (Formación López de Bertodano, Isla Marambio/Seymour Island); y de plioplatecarpinos y mosasaurinos en el Maastrichtiano tardío (Formación López de Bertodano, Isla Marambio/ Seymour Island). Los mosasaurios de la Península Antártica han sido estudiados principalmente desde un punto de vista sistemático y paleobiogeográfico. No obstante, la exploración de la microestructura ósea a menudo ofrece una fuente de información sobre hábitos de vida. Los estudios enfocados en aspectos osteohistológicos de los mosasaurios son relativamente escasos en comparación con otros grupos taxonómicos. Sheldon (1997) efectuó unanálisis microestructural de costillas pertenecientes a diversos géneros de mosasaurios, relacionando los diferentes patrones de microestructura ósea con los hábitos de vida que habrían tenido los diferentes mosasaurios. Recientemente, Houssaye (2008, 2009) y Houssaye et al. (2008) han estudiado la histología y, más específicamente, la microanatomía de diferentes taxones de mosasauroideos, discutiendo sus implicancias evolutivas y su relación con el hábito acuático de estos escamados. En el caso particular de los mosasaurios antárticos, el único antecedente publicado corresponde a una breve descripción de la microestructura de una vértebra de un mosasaurio maastrichtiano indeterminado recuperado de la Formación López de Bertodano en la Isla Marambio. En esta contribución, ampliando el conocimiento de mosasaurios de la cuenca James Ross, se realiza una descripción microanatómica y osteohistológica de dos vértebras pertenecientes a dos mosasaurios mosasaurinos exhumados de una misma formación, Formación López de Bertodano (Maastrichtiano tardío, Cretácico Tardío), de la Isla Marambio (Península Antártica) con el objeto de inferir algunos de sus hábitos de vida.

Talevi, M., Fernández, M. S, e Cerda, I. 2011.Osteohistología en Mosasaurios (Squamata: Mosasauridae) del Cretácico Tardío de la Cuenca James Ross (Península Antártica) Ameghiniana 48 (4): 668 – 673.

Gerald Grellet-Tinner,Lucas E. Fiorelli, y Rodrigo Brincalepe Salvador.

The water vapor conductance (GH2O) of the neosauropod eggs from the Lower Cretaceous Sanagasta nesting site in La Rioja Province, Argentina, was examined and compared with other Cretaceous Argentinean oological material. The 2900 mgH2O/day?Torr GH2O of the Sanagasta eggshells confirms an extremely moist nesting environment and supports field observations of dug-out nests in a geothermal setting. The observed thinning of the outer eggshell surface during incubation increases gas conductance and concomitantly decreases eggshell mechanical resistance during the late ontogenetic stages, thus facilitating embryonic development and hatching. The Sanagasta and Entre Ríos Province faveoloolithid eggs display the highest and comparable GH2O values and share several morphological and diagenetic characters, indicating comparable nesting strategy in geothermal settings. However, the faveoloolithid Yaminue´ and La Pampa Province specimens cluster together with lower GH2O values closer to the megaloolithid eggs. The GH2O of the megaloolithid egg Megaloolithus patagonicus was reconsidered and new results are now congruent with other reported megaloolithid GH2O values. Additionally, we hypothesize that Y-shaped pore canals of M. patagonicus, which upper sections reach only the top third or half eggshell thickness and, a wider section in the middle would not compromise the overall egg mechanical resistance like vertical pores connecting directly the outer to the inner eggshell surfaces. Such pore spatial arrangement and geometry would enhance, as the eggshell thins during incubation, a greater GH2O, GO2 and GCO2 and facilitate embryonic development in high moisture nesting contents. Overall, data suggests that neosauropod nesting and brooding behaviors were dependent on elevated moisture nesting environments.

Grellet-Tinner, G, Fiorelli, L. E., and Brincalepe Salvador, R. 2012. Water vapor conductance of the Lower Cretaceous Dinosaurian eggs from Sanagasta, La Rioja, Argentina: Paleobiological and Paleocological implications dor South American Faveloolithid and Megaloolithid eggs. PALAIOS, 27:35–47.

Alejandro Otero, Juan I. Canale, Alejandro Haluza y Jorge O. Calvo.

The Neuquén Basin has yielded a highly diverse fauna of sauropod dinosaurs. This group includes diplodocoids and titanosaurs. The plentiful record of titanosaur sauropods in the Upper Cretaceous of northern Patagonia is mostly restricted to derived titanosaurs included in the Titanosauridae (=Lithostrotia sensu Upchurch et al., 2004). Derived titanosaurs were traditionally characterized by the possession of strongly procoelous anterior-middle caudal vertebrae. This feature was used as a diagnostic trait to differentiate them from basal forms of titanosaurs with amphiplatyan or amphicoelous caudal vertebrae However recent discoveries have demonstrated that a great variation exists throughout the titanosaurian caudal series. In this sense, procoely appears to be non-continuous along the tail, implying a very different morphological scenario. In this paper we report a series of sauropod caudal vertebrae collected from the upper levels of the Candeleros Formation (Neuquén Group) near Villa El Chocón, Neuquén Province, Argentina. The materials, previously referred tentatively to Andesaurus, include a discontinuous series of mid- and mid-posterior caudal vertebrae,most of them including their haemal arches. The latter elements present an unusual morphology hitherto not reported in other sauropod dinosaurs.

Otero, A., Canale, J. I., Haluza, A. y Calvo, J. O. 2011 New Titanosaur with unusual haemal arches from the Upper Cretaceous of Neuquén Province, Argentina. Ameghiniana 48 (4): 655 – 661.

Diego Pol y Jaime Powell

A new basal mesoeucrocodylian, Lorosuchus nodosus gen. et sp. nov., from the Palaeocene of north-western Argentina is presented here. The new taxon is diagnosed by the presence of external nares facing dorsally, completely septated, and retracted posteriorly, elevated narial rim, sagittal crest on the anteromedial margins of both premaxillae, dorsal crests and protuberances on the anterior half of the rostrum, and anterior-most three maxillary teeth with emarginated alveolar margins. This taxon is most parsimoniously interpreted as a bizarr and highly autapomorphic basal member of Sebecidae, a position supported (amongst other characters) by the elongated bar-like pterygoid flanges, a laterally opened notch and fossa in the pterygoids located posterolaterally to the choanal opening (parachoanal fossa), base of postorbital process of jugal directed dorsally, and palatal parts of the premaxillae meeting posteriorly to the incisive foramen. Lorosuchus nodosus also shares with basal neosuchians a suite of derived characters that are interpreted as convergently acquired and possibly related to their semiaquatic lifestyle. The phylogenetic analysis used for testing the phylogenetic affinities of L. nodosus depicts Sebecidae as the sister group of Baurusuchidae, forming a monophyletic Sebecosuchia that is deeply nested within Notosuchia. Alternative phylogenetic placements of Sebecidae, such as the recently proposed affinities with peirosaurids, were also evaluated within the context of the present data matrix and found to be only marginally suboptimal.

Pol, D. y Powell, J. 2011. A new sebecid mesoeucrocodylian from the Rio Loro Formation (Palaeocene) of north-western Argentina. Zoological Journal of the Linnean Society, 2011, 163, S7–S36.

Alejandro Haluza, Juan I. Canale, Alejandro Otero, Leandro M. Pérez & Carlos A. Scanferla

The fossil record of rebbachisaurid sauropods has greatly increased recently (Calvo and Salgado, 1995; Bonaparte, 1996; Dalla Vecchia, 1998; Sereno et al., 1999, 2007; Medeiros and Schultz, 2001; Pereda-Suberbiola et al., 2001, 2003; Salgado et al., 2004, 2006; Gallina and Apesteguía, 2005; Apesteguía, 2007; Mannion, 2009). The first fossil remains belonging to this group were described by Nopcsa (1902) but only recently recognized as a rebbachisaurid (Calvo and Salgado, 1995; Apestegu´ıa, 2007). Lavocat (1954) erected Rebbachisaurus garasbae, which has a scapula with broad, ‘racquet’-shaped blade, and a mid-dorsal vertebra with a very tall neural spine. This family is mostly known from rather fragmentary remains, and many specimens are unpublished or only partially described (Gallina and Apestegu´ıa, 2005). In this contribution, we present new materials assignable to Rebbachisauridae, recovered from the Huincul Formation, Neuquén Group, near Villa El Chocón, Neuquén Province. The lowermost section of this geological unit has yielded other dinosaur taxa, such as Skorpiovenator bustingorryi (Canale et al., 2009). The rebbachisaurid remains correspond to a single, partially articulated, and exceptionally preserved skeleton, which includes cervical and dorsal vertebrae, thoracic ribs, scapula, and a humerus. The importance of studying complete serial elements of the skeleton (e.g., vertebral series) lies on the ability to track specific elements (i.e., landmarks), which are useful to unambiguously recognize homologous structures (Wilson, 1999; Otero et al., In press; Wilson et al., 2011). In this regard, the preserved cervicodorsal series described herein gives remarkable anatomical and systematic information, allowing the recognition of the transitional morphology, topology, and extent of the vertebral laminae

Haluza, A., Canale, J. I., Otero, A.,  Pérez, L. M., and Scanferla, C., 2012.Changes in vertebral laminae across the cervicodorsal transition of a well-preserved rebbachisaurid (Dinosauria, Sauropoda) from the Cenomanian of Patagonia, Argentina, Journal of Vertebrate Paleontology, 32:1, 219-224.