UPPER CRETACEOUS DINOSAUR EGGS AND EGGSHELLS FROM SANAGASTA (LA RIOJA, ARGENTINA): TAXONOMIC IMPLICATIONS AND INFERENCES FOR THE OOLOGICAL PARAPHYLETIC CLASSIFICATION

LUCAS FIORELLI; GERALD GRELLET-TINNER

Teruel, España

Simposio; 10th Mesozoic Terrestrial Ecosystems Symposium; 2009

Universidad Autónoma de Madrid

The Sanagasta dinosaur nesting site in La Rioja Province (Argentina) has recently yielded an impressive amount of eggs and egg clutches, perhaps only paralleled in concentration by the famous Auca Mahuevo locality (Argentina). However, no embryo in ovo has been recovered to date to insure a positively taxonomic identification of these eggs. The present investigation centers on these egg morphology and eggshell microstructure for taxonomic identification purposes and paleobiological interpretations. Taxonomic identification of these specimens was sought by comparison with other identified dinosaur eggs and also with the established oological parataxonomic classification. Although the eggshells display considerable variations in their thickness and morphology, observations support that pristine specimens display only one single structural layer that consists of acicular calcitic crystals. This character would place the parent lineage within Sauropoda. Regarding the parataxonomic oological classification, several morphotypes are noted within a single egg according to the topological position and thickness of the eggshell on the specimen. The thin shells display features similar to those assigned to “megaloolithid” eggs, conversely thicker specimens with elongated eggshell units and pore channels that exhibit complex different ramifications, resemble “faveoloolithid” eggs. Other eggshells characters, namely the external and internal surface morphologies, pore apertures, and eggshell units, which exhibit convex growth lines, are also taken in consideration and support the previously stated observations. Although this research is in its infancy, preliminary conclusions advocate that 1) the dinosaurs that laid the eggs at Sanagasta were likely sauropods and 2) two oofamilies of the parataxonomic classification are expressed concomitantly in several eggs. The latter supports previous observations that many categories of the egg parataxonomy are artificial groups. More investigations are planned for 2009 and 2010 to refine our results.