CONICET | Buscador de Institutos y Recursos Humanos

The exceptional Konservat Laggerstate ?Loma del Pterodaustro? (Lagarcito Formation,Aptian-Albian) from San Luis Province (Argentina) has yielded hundred?s of fragmentaryand articulated specimens including adults, sub-adults, juveniles and one embryo ofPterodaustro guinazui. Here we present the first 3D fossil egg from Lagarcito Formationfound at the same horizon where the embryos was discovered. The new and incompletespecimen includes the narrow pole and about 1/3 of the entire egg. The eggshellmorphology and composition was analyzed with SEM and EDS and compared with theeggshell associated with the previously discovered embryo. The calcite eggshell is 50μmthick. Layer 1, without noticeable nucleation centers, is formed by horizontal tabularcrystals. Layer 2 is formed by columns of tabular crystals as the layer 1 but shorter andnarrow. The outer most third layer includes amorphous granular material, which iscomparable to the external covering of modern and extinct Phoenicopteriformes andPedicidiformes eggs. The eggshell thickness is not apparently congruent with the eggshellfrom the embryo described in 2004, which structure and thickness matches perfectly withthe second layer of the new specimen. The lack of layer 1 in the embryo could be explainedby calcium reabsorption during embryogenesis and/or a diagenetic process. The absence ofspherulite in a probably pterosaur´s eggshell and their presence in dinosaurian eggshells(including birds) imply that this phylogenetic character may be autapomorphic to thepterosaur and crocodilian clades. Considering the oological congruence, the restrictedvertebrate fauna in the ?Loma del Pterodaustro?, coupled with the particular taphonomicconditions of this site, this new fossil most likely represents the first occurrence of a 3Dpterosaur egg in the fossil record.

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