C&aacute;scaras de huevos de dinosaurios de la Formaci&oacute;n Allen (Campaniano-Maastrichtiano), en Salitral Moreno, provincia de R&iacute;o Negro, Argentina  <span class="so-article-trans-title" dir="auto"> Translated title: Dinosaur eggshells from the Allen Formation (Campanian-Maastrichtian), at Salitral Moreno, R&iacute;o Negro Province, Argentina </span>

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Abstract

En el presente trabajo se describen en detalle dos morfotipos de cáscaras de huevos de dinosaurios hallados en Salitral Moreno (Formación Allen, Cretácico Superior), en la provincia de Río Negro. En cuanto a su determinación parataxonómica, se crea Patagoolithus salitralensis un nuevo oogénero et ooespecie nov., correspondiente a la oofamilia Megaloolithidae y el otro morfotipo se asigna a ?Faveoloolithidae oogen. et oospec. indet. Se realiza una detallada descripción ultraestructural de ambos morfotipos, como así también el análisis químico y mineralógico de ?Faveoloolithidae oogenero et oospecie indet. En las secciones estudiadas se reconocieron tres niveles con cáscaras de huevos. En el inferior (NH1) las cáscaras correspondientes a Patagoolithus salitralensis están asociadas a una diversa fauna de dinosaurios, quelonios e invertebrados. Los fragmentos de cáscaras son muy escasos y dispersos, lo que podría indicar paleollanuras aluviales o huevos desintegrados. En los niveles NH2 y NH3 sólo se encontraron cáscaras correspondientes a ?Faveoloolithidae oogen. et oospec. indet. El NH2 presenta variaciones laterales importantes en las distintas columnas, en el grado de transporte y en la densidad de los fragmentos. El NH3 presenta pequeños fragmentos de cáscaras que se hacen más escasos hacia la parte superior. En este nivel, como en el NH1, se observan rizolitos y estructuras alveolares características de calcretes, lo cual podría indicar la presencia de un paleosuelo.

Translated abstract

A detailed description of two morphotypes of dinosaur eggshells from Salitral Moreno, Rio Negro Province (Allen Formation, Upper Cretaceous) is presented. One of them is described as Patagoolithus salitralensis, a new oogenus et oospecies nov. belonging to the Megaloolithidae, and the second is referred as ?Faveoloolithidae, oogenus et oospecies indet. A detailed ultrastructural description of both morphotypes is provided, as well as, the chemical and mineralogical analysis of ?Faveoloolithidae oogen. et oospec. indet. In the studied sections, three eggshell-bearing levels were recognized. In the lower one (NH1) Patagoolithus salitralensis is associated to a diverse fauna of dinosaurs, chelonians and invertebrates, and the few shell fragments are dispersed, suggesting deposition in an alluvial plain or disintegrated eggs. In NH2 and NH3, only eggshells of ?Faveoloolithidae oogenus et oospecies indet. were found. NH2 shows lateral variations in the inferred degree of transport and density of the shell fragments in different sections. NH3 bears small shell fragments of the same morphotype decreasing in number towards the top. NH1 and NH3 bear rizolithes and alveolar structures, characteristic of calcretes, which could be indicative of palaeosoils.

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Sauropod dinosaur embryos from the Late Cretaceous of Patagonia

Frankie Jackson, Marilyn D. Fox, Anusuya Chinsamy … (1998)

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Models for fossil concentrations: paleobiologic implications

Susan Kidwell (1986)

Four basic types of skeletal concentrations are modeled in terms of changes in sedimentation rate alone. The model categorizes fossil concentrations on the relatively objective basis of their bed contacts, and uses this criterion to infer directional shifts in net sedimentation. This radical simplification of accumulation histories, in which hardpart input is held constant, yields a surprisingly powerful model capable of predicting a broad spectrum of taphonomic and paleobiologic phenomena. Type I concentrations grade from less fossiliferous sediments and terminate in omission surfaces; if hardpart supply is held constant, they record a slowdown from positive to zero net sedimentation. Type II concentrations are the same as Type I but terminate in erosion surfaces (slowdown to negative net sedimentation), and Type III and IV concentrations are characterized by basal erosion or omission surfaces, respectively, grade upward into less fossiliferous sediments, and record increases in net sedimentation from negative or zero rates to positive rates. According to the model, samples collected from successive horizons within any of these shell beds will differ in the degree and type of post-mortem bias owing to differing histories of hardpart exposure at the depositional interface. Moreover, because rates of sediment accumulation govern the abundance of hardparts at the depositional interface and thus many of the physical characteristics of the benthic habitat, the dynamics of fossil accumulation have direct consequences for the structure of benthic communities (taphonomic feedback) and for ecologically controlled species morphometry. The model is highly robust to fluctuations in hardpart input, as judged by its ability to correctly infer modes of formation of concentrations in synthetic stratigraphic sections. In addition, field examples of Type I–IV concentrations show independent evidence of formation during intervals of reduced net sedimentation, and many exhibit trends in taphonomic and paleobiologic features expected from the postulated changes in net sedimentation. The model thus provides a testable working hypothesis for the accumulation of fossil material in a wide range of environments, and should be applicable to concentrations of any taxonomic composition, state of preservation, or geologic age. The power and robustness of this heuristic model in fact argue that fossil-rich and fossil-poor strata provide fundamentally different records of past conditions, and that sedimentation rather than hardpart input is the primary control on the nature of the fossil record.