Trabajos de campo confirman el enorme tamaño del nuevo ejemplar

0 comentarios Publicado por Leonardo Filippi en 8:51

Durante la primera mitad del mes de abril, el MAU (Museo Municipal Argentino Urquiza), Rincón de los Sauces, Neuquén, reanudó los trabajos de campo en Cañadón Mistringa. En este sitio fue hallado durante el 2012 un enorme ejemplar de dinosaurio saurópodo titanosaurio. Durante estos trabajos se recuperaron algunos huesos que dan cuenta del gran tamaño del animal: una escápula incompleta que se estima superaría el 1,50 m de longitud y una enorme vértebra cervical (bochón de la foto) cuyas medidas estimadas superarían el 1,20 m de ancho, 0,90 m de largo y 1 m de alto aproximadamente. Las tareas de recuperación de este gigante recién comienzan, por lo que todavía será necesario remover varios metros cúbicos de roca, para así, extraer nuevas piezas que permitan estimar el tamaño real del ejemplar, el cual se cree, estaría entre los 30 y 35 m de longitud.

 

Análisis de cáscaras de huevos de dinosaurio de la Formación Allen, Río Negro, Argentina.

0 comentarios Publicado por Leonardo Filippi en 8:31


Mariela S. Fenández
 
El presente estudio es una contribución más al conocimiento de la parataxonomía de las cáscaras de huevos de dinosaurios procedentes del Salitral de Santa Rosa y Salitral Ojo de Agua de la provincia de Río Negro, Argentina. Para dicho trabajo fueron estudiados 4469 fragmentos de cáscaras de huevos de la Formación Allen, Cretácico Superior (Campaniano-Maastrichtiano). Doce de estas cáscaras fueron sometidas a un Análisis de Componentes Principales, para clasificarlas y analizar las relaciones entre los caracteres utilizados comúnmente en las clasificaciones parataxonómicas. Por otra parte se estudiaron 4264 cáscaras con lupa binocular, 57 cáscaras con microscopio óptico y microscopio de polarización y por último 14 cáscaras con microscopio electrónico de barrido. Fueron identificados dos grandes grupos, cáscaras del tipo 1 afines a la oofamilia Megaloolithidae con cinco subtipos y cáscaras del tipo 2, sin subtipos. Los caracteres relevantes encontrados con el estudio de ACP fueron: el espesor de la cáscara, la anchura de las unidades de cáscara, el diámetro de los nódulos y el diámetro de las mamilas. Los diferentes tipos de cáscaras registrados fueron comparados con diversos ootaxones de América del Sur y del resto del mundo.
 
Fernández, M.S. 2013. Análisis de cáscaras de huevos de Dinosaurios de la Formación Allen, Cretácico Superior de Río Negro (Campaniano-Maastrichtiano): Utilidad de los macrocaracteres de interés parataxonómico. Ameghiniana 50 (1): 79-97.

 

Avian eggs from the Late Cretaceous of Patagonia

0 comentarios Publicado por Leonardo Filippi en 8:22


Mariela S. Fernández, Rodolfo A. García, Lucas Fiorelli, Alejandro Scolaro, Rodrigo B. Salvador, Carlos N. Cotaro, Gary W. Kaiser y Gareth J. Dyke

We report the first evidence for a nesting colony of Mesozoic birds on Gondwana: a fossil accumulation in Late Cretaceous rocks mapped and collected from within the campus of the National University of Comahue, Neuquén City, Patagonia (Argentina). Here, Cretaceous ornithothoracine birds, almost certainly Enanthiornithes, nested in an arid, shallow basinal environment among sand dunes close to an ephemeral water-course. We mapped and collected 65 complete, nearcomplete, and broken eggs across an area of more than 55 m2. These eggs were laid either singly, or occasionally in pairs, onto a sandy substrate. All eggs were found apparently in, or close to, their original nest site; they all occur within the same bedding plane and may represent the product of a single nesting season or a short series of nesting attempts. Although there is no evidence for nesting structures, all but one of the Comahue eggs were half-buried upright in the sand with their pointed end downwards, a position that would have exposed the pole containing the air cell and precluded egg turning. This egg position is not seen in living birds, with the exception of the basal galliform megapodes who place their eggs within mounds of vegetation or burrows. This accumulation reveals a novel nesting behaviour in Mesozoic Aves that was perhaps shared with the non-avian and phylogenetically more basal troodontid theropods.
 
Fernández MS, García RA, Fiorelli L, Scolaro A, Salvador RB, et al. (2013) A Large Accumulation of Avian Eggs from the Late Cretaceous of Patagonia (Argentina) Reveals a Novel Nesting Strategy in Mesozoic Birds. PLoS ONE 8(4): e61030. doi:10.1371/journal.pone.0061030

 

Morfología e histología de los osteodermo de un nuevo crocodyliforme de Rincón de los Sauces, Neuquén.

0 comentarios Publicado por Leonardo Filippi en 14:50



Filippi L. S., Cerda I. A. y Garrido, A. C.
 
Resumen. Se describen osteodermos de un nuevo ejemplar de crocodyliforme hallado en un afloramiento correspondiente a niveles de la Formación Plottier (Coniaciano tardío) de la localidad de Puesto Hernández, en inmediaciones de la localidad de Rincón de los Sauces, Provincia del Neuquén. Los osteodermos estudiados, que son parte del material hallado, están integrados por: región dorso-sacra, osteodermos apendiculares asociados al fémur derecho, región proximoventral de osteodermos caudales articulados y osteodermos aislados. La histología de los osteodermos permitió determinar que están constituidos por una corteza compacta que circunda una región interna más porosa. Fue posible reconocer marcas de crecimiento (annuli) en prácticamente todo el tejido compacto, pudiendo determinarse una edad mínima de 18 años para el espécimen estudiado. Los osteodermos exhiben caracteres que permiten preliminarmente asignar al ejemplar, como un Mesoeucrocodylia cercanamente relacionado con Peirosauridae.

Abstract. Osteoderms of a new crocodyliform specimen recovered from the Puesto Hernández locality are described here, found in sediments of the Plottier Formation (late Coniacian), near Rincón de los Sauces city, Neuquén Province. The studied osteoderms, that are part of the associated material, include: dorso-sacral region, appendicular osteoderms associated to the right femur, proximoventral region of articulated caudal osteoderms, and isolated osteoderms. The histology of the osteoderms allowed determining they have a compact cortex that surrounds a more cancellous internal region. It was possible to recognize growth marks (annuli) in the entire compact tissue, indicating a minimum age of 18 years for the studied specimen. The osteoderms have characters that allow preliminarily assigning the specimen to Mesoeucrocodylia closely related to Peirosauridae.
Filippi, L.S., Cerda, I.A. y Garrido, A. C. 2013 Morfología e histología de los osteodermos de un peirosauridae de la Cuenca Neuquina. Ameghiniana 50 (1):3-13.


 

 

Early basicranial evolution and the origins of Crocodyliformes

0 comentarios Publicado por Leonardo Filippi en 15:06

 

Diego Pol, Oliver W. M. Rauhut, Agustina Lecuona, Juan M. Leardi, Xing Xu and James M. Clark

Extant crocodylians have a limited taxonomic and ecological diversity but they belong to a lineage (Crocodylomorpha) that includes basal and rather generalized species and a highly diverse clade, Crocodyliformes. The latter was among the most successful groups of Mesozoic tetrapods, both in terms of taxonomic and ecological diversity. Crocodyliforms thrived in terrestrial, semiaquatic, and marine environments, and their fossil diversity includes carnivorous, piscivorous, insectivorous, and herbivorous species. This remarkable ecological and trophic diversity is thought only to occur in forms with a completely akinetic skull, characterized by a functionally integrated and tightly sutured braincase-quadrate-palate complex. However, the patterns of evolutionary change that led to the highly modified skull of crocodyliforms and that likely enabled their diversification remain poorly understood. Herein, a new basal crocodylomorph from the Late Jurassic of Patagonia is described, Almadasuchus figarii gen. et sp. nov. The new taxon is known from a well-preserved posterior region of the skull as well as other craniomandibular and postcranial remains. Almadasuchus figarii differs from all other crocodylomorphs in the presence of six autapomorphic features, including the presence of a large lateral notch on the upper temporal bar, an otic shelf of the squamosal that is wider than long, a deep subtriangular concavity on the posterolateral surface of the squamosal, and an elongated pneumatopore on the ventral surface of the quadrate. Phylogenetic analysis focused on the origin of Crocodyliformes places Almadasuchus as the sister group of Crocodyliformes, supported by synapomorphic features of the skull (e.g. subtriangular basisphenoid, absence of basipterygoid process, absence of a sagittal ridge on the frontal, and a flat anterior skull roof with an ornamented dorsal surface). New braincase information provided by Almadasuchus and other crocodylomorphs indicates that most of the modifications on the posterior region of the skull of crocodyliforms, including the strongly sutured braincase, quadrate, and the extensive secondary palate appeared in a stepwise manner, and pre-dated the evolutionary changes in the snout, jaws, and dentition. This indicates that the progressively increased rigidity of the skull provided the structural framework that allowed the great ecological diversification of crocodyliforms during the course of the Mesozoic. The phylogenetic pattern of character acquisition inferred for the strongly sutured (akinetic) skull and the appearance of more diverse feeding behaviours that create high mechanical loads on the skull provides another interesting parallel between the evolution of Mesozoic crocodyliforms and the evolutionary origins of mammals.
Pol, D., Rauhut, O.W.M., Lecuona, A., Leardi, J. M., Xu. X. and Clark, J.M. 2013 A new fossil from the Jurassic of Patagonia reveals the early basicranial evolution and the origins of Crocodyliformes. Biological Reviews. doi: 10.1111/brv.12030
 

 

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