A Basal Lithostrotian Titanosaur with a Complete Skull from Patagonia, Argentina

0 comentarios Publicado por Leonardo Filippi en 12:05

 
 

Rubén D. F. Martínez, Matthew C. Lamanna, Fernando E. Novas, Ryan C. Ridgely, Gabriel A. Casal, Javier E. Martínez, Javier R. Vita & Lawrence M. Witmer

We describe Sarmientosaurus musacchioi gen. et sp. nov., a titanosaurian sauropod dinosaur from the Upper Cretaceous (Cenomanian - Turonian) Lower Member of the Bajo Barreal Formation of southern Chubut Province in central Patagonia, Argentina. The holotypic and only known specimen consists of an articulated, virtually complete skull and part of the cranial and middle cervical series. Sarmientosaurus exhibits the following distinctive features that we interpret as autapomorphies: (1) maximum diameter of orbit nearly 40% rostrocaudal length of cranium; (2) complex maxilla-lacrimal articulation, in which the lacrimal clasps the ascending ramus of the maxilla; (3) medial edge of caudal sector of maxillary ascending ramus bordering bony nasal aperture with low but distinct ridge; (4) ‘tongue-like’ ventral process of quadratojugal that overlaps quadrate caudally; (5) separate foramina for all three branches of the trigeminal nerve; (6) absence of median venous canal connecting infundibular region to ventral part of brainstem; (7) subvertical premaxillary, procumbent maxillary, and recumbent dentary teeth; (8) cervical vertebrae with ‘strut-like’ centroprezygapophyseal laminae; (9) extremely elongate and slender ossified tendon positioned ventrolateral to cervical vertebrae and ribs. The cranial endocast of Sarmientosaurus preserves some of the most complete information obtained to date regarding the brain and sensory systems of sauropods. Phylogenetic analysis recovers the new taxon as a basal member of Lithostrotia, as the most plesiomorphic titanosaurian to be preserved with a complete skull. Sarmientosaurus provides a wealth of new cranial evidence that reaffirms the close relationship of titanosaurs to Brachiosauridae. Moreover, the presence of the relatively derived lithostrotian Tapuiasaurus in Aptian deposits indicates that the new Patagonian genus represents a ‘ghost lineage’ with a comparatively plesiomorphic craniodental form, the evolutionary history of which is missing for at least 13 million years of the Cretaceous. The skull anatomy of Sarmientosaurus suggests that multiple titanosaurian species with dissimilar cranial structures coexisted in the early Late Cretaceous of southern South America. Furthermore, the new taxon possesses a number of distinctive morphologies such as the ossified cervical tendon, extremely pneumatized cervical vertebrae, and a habitually downward facing snout that have rarely, if ever, been documented in other titanosaurs, thus broadening our understanding of the anatomical diversity of this remarkable sauropod clade. The latter two features were convergently acquired by at least one penecontemporaneous diplodocoid, and may represent mutual specializations for consuming low-growing vegetation.

Martínez RDF, Lamanna MC, Novas FE, Ridgely RC, Casal GA, Martínez JE, et al. (2016) A Basal Lithostrotian Titanosaur (Dinosauria: Sauropoda) with a Complete Skull: Implications for the Evolution and Paleobiology of Titanosauria. PloS ONE 11(4): e0151661. doi:10.1371/journal. pone.0151661

 

A Norian lagerpetid dinosauromorph from the Quebrada del Barro Formation, Argentina

0 comentarios Publicado por Leonardo Filippi en 13:34



Ricardo N. Martínez, Cecilia Apaldetti, Gustavo A. Correa, And Diego Abelín

The early evolution of Ornithodira the clade including pterosaurs and dinosaurs is poorly known. Until a decade ago, the basal radiation of Dinosauromorpha, the clade including dinosaurs and birds, was poorly understood because of the poor fossil record restricted to specimens known from the Ladinian Chañares Formation in Argentina. Over the last years the discovery of several non-dinosaurian dinosauromorphs dramatically expanded this record and also demonstrated that this group –previously restricted to de Middle Triassic survived at least well into the Norian. Although Norian non-dinosaurian dinosauromorphs have been reported from several regions around the world, the only known Norian non-dinosauriform dinosauromorphs Dromomeron romeri Irmis, Nesbitt, Padian, Smith, Turner, Woody, and Downs and Dromomeron gregorii Nesbitt, Irmis, Parker, Smith, Turner, and Rowe come from North America. We report here the first record from the Southern Hemisphere of a non-dinosauriform dinosauromorph, Dromomeron gigas sp. nov., from the Norian Quebrada del Barro Formation, northwestern Argentina. A phylogenetic analysis recovers Dromomeron gigas nested into the monophyletic group Lagerpetidae, and as the sister taxon to Dromomeron romeri. The inclusion of D. gigas within Lagerpetidae suggests that body size increased in this lineage over time, as was previously demonstrated for Dinosauriformes as a whole, and that lagerpetids reached a larger size than previously thought. Finally, the new finding provides new information on the basal radiation of Dinosauromorpha constituting the first record of a Norian association of dinosaurs with non-dinosauriform dinosauromorphs outside North America.

Ricardo N. Martínez, Cecilia Apaldetti, Gustavo A. Correa, Diego Abelín (2016). A Norian lagerpetid dinosauromorph from the Quebrada del Barro Formation, northwestern Argentina. Ameghiniana 53: 1–13.

 

A new specimen of Velocisaurus unicus from Río Negro Province, Argentina

0 comentarios Publicado por Leonardo Filippi en 14:05


Federico Brissón Egli, Federico L. Agnolín, And Fernando Novas

Abelisauroids are the most abundant theropods in the Cretaceous beds of Patagonia. They are traditionally subdivided into large-sized Abelisauridae and smaller Noasauridae. Here, we describe a new specimen of the small enigmatic abelisauroid Velocisaurus unicus Bonaparte, 1991, which was previously known from a single incomplete specimen from Neuquén City, Neuquén Province, Patagonia. The new material comes from the Santonian Bajo de la Carpa Formation (Late Cretaceous) at the Paso Córdoba locality, Río Negro Province. It comprises an almost complete left hind limb and offers novel information about the anatomy of this poorly known abelisauroid. The new material shows that Velocisaurus is remarkable in having a very short, stout, and anteriorly bowed femur, which has a notably subtriangular cross-section at its proximal end. The tibia is long and slender, and the anterior surface of the distal end is anteroposteriorly flat and transversely expanded, with an enlarged surface for the ascending process of the astragalus. The pes has a stout third metatarsal, rod-like metatarsals II and IV, and highly modified phalanges of digit IV. The unique combination of characters of Velocisaurus indicates that this taxon belongs to a still poorly understood radiation of gracile-limbed abelisauroids. The inclusion of Velocisaurus in a comprehensive phylogenetic analysis recovers a monophyletic Noasauridae, but with only very weak support. Detailed analysis of features supporting the inclusion of Velocisaurus within Noasauridae is discussed, and their implications for abelisauroid phylogeny are revisited.
Federico Brissón Egli, Federico L. Agnolín & Fernando Novas 2016. A new specimen of Velocisaurus unicus (Theropoda, Abelisauroidea) from the Paso Córdoba locality (Santonian), Río Negro, Argentina, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2016.111915

 

Presentan un nuevo dinosaurio en el MAU: Viavenator exxoni

0 comentarios Publicado por Leonardo Filippi en 20:26


En el día de ayer, se llevó adelante la presentación formal del nuevo dinosaurio del MAU, Museo Municipal Argentino Urquiza, Rincón de los Sauces, Neuquén: Viavenator exxoni, un nuevo género y especie de abelisaurio que aporta información relevante que permite avanzar en el conocimiento de este grupo de terópodos.
Este ejemplar, corresponde al primer dinosaurio carnívoro de la colección del MAU, por lo que todo el equipo del trabajo del museo y los colegas que han participado de su estudio, se encuentran muy satisfechos. Si bien el potencial del área La Invernada, en el cual se viene trabajando desde hace un poco más de tres años, es inmenso, la publicación de este dinosaurio, representa el primero de una serie de otros ejemplares que han sido recuperados allí, entre los que se mencionan, varios dinosaurios titanosaurios, una descena de ejemplares de tortugas y peces.
Los huesos orginales de Viavenator se encontrarán temporalmente exhibidos al público en el laboratorio del Museo hasta fines de Marzo.

 

A new Upper Cretaceous Titanosaur nesting site from La Rioja, Argentina

0 comentarios Publicado por Leonardo Filippi en 13:24


E. Martin Hechenleitner, Lucas E. Fiorelli, Gerald Grellettinner,  Léa Leuzinger, Giorgio Basilici, Jeremías R. A. Taborda, Sergio R. De La Vega And Carlos A. Bustamante

            Cretaceous titanosaur nesting sites are currently known only from Europe, Asia and South America. In the latter, only the Auca Mahuevo and Sanagasta nesting sites have been confidently assigned to this clade of sauropod dinosaurs. Here we report the discovery of the first eggs and egg clutches found at Tama, a new Upper Cretaceous fossiliferous locality in the Los Llanos Formation, Sierra de Los Llanos (La Rioja, NW Argentina). At least five egg clutches, several partially preserved, isolated eggs and many eggshell fragments were discovered in a single outcrop of a sandstone horizon which represents a cumulative palaeosol profile. Although the mechanical and digital preparation of eggs did not reveal any embryonic remains in ovo, the morphology of the eggs and eggshells closely matches that of titanosaur eggs and eggshells found worldwide. The morphology and spatial grouping of the titanosaur eggs from Tama, along with geological observations support a burrow-nesting strategy for these dinosaurs. Although the Sanagasta and Tama eggs were found in the same stratigraphical unit and share several morphological characters, they clearly differ in shell thickness and egg size. This, coupled with the interpretation of different sedimentary contexts for these nesting sites, strongly suggests that at least two different titanosaur species nested in La Rioja during the Late Cretaceous, using different nesting strategies. The occurrence of this new titanosaur nesting site in a semiarid palaeoenvironment represents an interesting case study for the reproductive biology of the titanosaur dinosaurs, particularly their labile nesting behaviour.

Hechenleitner, EM, Fiorelli, LE, Grellettinner, G,  Leuzinger, L, Basilici, G, Taborda, JRA,  De La Vega, SR And Bustamante, CA. 2016. A new Upper Cretaceous Titanosaur nesting site from La Rioja (Nw Argentina), with implications for Titanosaur nesting strategies. Palaeontology, pp. 1–14.

 

Shell bone histology of the long-necked chelid Yaminuechelys (Testudines: Pleurodira) from the late Cretaceous-early Palaeocene of Patagonia

0 comentarios Publicado por Leonardo Filippi en 6:56

 
 

Juan Marcos Jannello, Ignacio A. Cerda, Marcelo S. de la Fuente

            Yaminuechelys is a long-necked chelid turtle whose remains have been recovered from outcrops of the Santonian- Maastrichtian and Danian of SouthAmerica.With the purpose of providing data about shell sculpturing origin and palaeoecology, the bone histology of several shell elements (including neural, costal, peripheral and plastral plates) of Yaminuechelys is described herein. Histological analysis reveals that Yaminuechelys shares with Chelidae the presence of interwoven structural fibre bundles in the external cortex, and parallel-fibred bone of the internal cortex. The presence of resorption lines in several samples indicates that the particular ornamentation of the external surfaces originated, at least in part, by focalized resorption and new bone deposition. This mechanism for ornamentation origin and maintenance is here described for the first time in a turtle. Compactness of the shell bones is consistent with an aquatic habitat, which supports previous hypothesis based on palaeoenvironmental and morphological data.

Janello, JM, Cerda, IA & de la Fuente, MS. 2016. Shell bone histology of the long-necked chelid Yaminuechelys (Testudines: Pleurodira) from the late Cretaceous—early Palaeocene of Patagonia with comments on the histogenesis of bone ornamentation. Sci Nat. 103:26.DOI 10.1007/s00114-016-1346-3.

 

New Peirosaurid from Cerro Lisandro Formation, Neuquén Group, Patagonia Argentina

0 comentarios Publicado por Leonardo Filippi en 6:36


Francisco Barrios, Ariana Paulina-Carabajal y Paula Bona

Peirosaurids are a group of Cretaceous continental crocodyliforms from Gondwana. Two species are known from the Neuquén Group in Argentina: Lomasuchus palpebrosus (Portezuelo Formation, late Turonian–early Coniacian) and Gasparinisuchus peirosauroides (Bajo de la Carpa and Anacleto formations, Santonian and early Campanian, respectively). Here, we describe the first peirosaurid from the Cerro Lisandro Formation, Bayomesasuchus hernandezi gen. et sp. nov. The material corresponds to a fragmentary skull and mandible. Although fragmentary, this is the most complete crocodyliform specimen recorded for the Cerro Lisandro Formation. In a phylogenetic analysis Bayomesasuchus is depicted in a polytomy together with South American peirosaurids and the African form Hamadasuchus rebouli.

Barrios, F. Paulina-Carabajal, A, y Bona Paula. 2016. A new Peirosaurid (Crocodyliformes, Mesoeucrocodylia) from the Upper Cretaceous of Patagonia, Argentina. Ameghiniana 53 (1):14-25.

 

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