Oldest Cretaceous sauropods eggs from Patagonia, Chubut, Argentina (Cerro Barcino Formation, Aptian-Albian)

ELOISA ARGAÑARAZ; GERALD GRELLE-TINNER; LUCAS FIORELLI; MARCELO KRAUSE

San Juan

Congreso; IV Congreso Latinoamericano Paleontologia de Vertebrados; 2011

The Late Cretaceous of South America has yielded several important nesting sites and isolated dinosaur eggs and eggshells. However, the record of Early Cretaceous eggs is not yet well represented on this continent, besides the Hauterivian?Aptian nesting site from Sanagasta in La Rioja Province, Argentina. We present, here, the oldest Cretaceous sauropod eggs from Patagonia. These two dinosaur eggs, the first ones from Chubut (Patagonia), were discovered in the Cerro Castaño Member of the Aptian?Albian Cerro Barcino Formation that outcrops at Huanimán. The specimens were preserved in a fine, pedogenized, tuffaceous sandstone in proximal floodplain facies and multiepisodic channel facies. Sedimentary analyses suggest the presence of an anastomosing fluvial system, probably related to sub humid to semiarid paleoclimatic conditions. The eggshells morphology is similar to other megaloolithid eggs (a paraphyletic egg parataxonomic group) from Patagonia, namely Auca Mahuevo (Neuquén), positively identified as sauropods titanosaurs by embryos in ovo, and Salitral Moreno (Río Negro). However, this new Chubut material exhibits a structural eggshell feature not previously reported. A horizontal pore canal network is clearly visible near and under the outer nodular eggshell surface, differently from the Neuquén eggs where it overlays the membrana testacea. This morphological feature and the 1.5 mm thick eggshell illustrate a novel adaptation to this specific nesting environment. Although only two isolated eggs were found in Huanimán, this discovery may imply the existence of a more substantial nesting site with several eggs clutches like other sauropods nesting sites.