Micro and ultrastructural characterization of the eggshell in dinosaurs eggs from Sanagasta (Upper Cretaceous), La Rioja Province, Argentina

LUCAS FIORELLI; GERALD GRELLET-TINNER

San Rafael, Mendoza

Jornada; Jornadas Argentinas de Paleontologías de Vertebrados; 2009

Museo de Historia Natural de San Rafael

The preliminary studies of the Sanagasta nesting in La Rioja Province focused on the mapping and distributional patterns and characteristics of the nesting site, with an overview of the egg structural features coupled with primary taphonomic and paleobiologic interpretations. Our present investigation centers on the eggshell microstructure of these eggs to facilitate their comparison with other dinosaur eggs from South America. Although, the eggshells display considerable variationsin their thickness and morphology, observations support that the non-altered eggshells have only one single structural layer consisting of acicular calcitic crystals. Furthermore, the eggshell units show under high magnification convex growth lines formed by rhombohedric crystals. There are several eggshell unit morphotypes (relying on the traditional eggshell parataxonomy) in the same eggshell, according to various factors such as topological position and eggshell thickness. The thin shells display similar units to those present in megaloolithid eggs, whereas thicker specimens exhibitelongated units with morphologically diverse ramifications similar to faveoloolithid eggs, as the pore channels exhibit complex and different morphological structures. Other eggshells characters, such as the eggshell external and internal surfaces, pore-canal network and its apertures are addressed in addition to taphonomic attributes and their paleobiologic implications. The primary conclusion of this study supports previous observations that the egg parataxonomy is paraphyletic and the archosaurian oologic classification consists of unnatural groups.