Firts record of dinosaur eggs from La Invernada fossil site (Bajo de la Carpa Formation, Santonian) Rincón de los Sauces, Neuquén, Argentina

ARIELA MENDEZ; MARIELA SOLEDAD FERNÁNDEZ; LEONARDO FILIPPI

General Roca

Congreso; Reunión de comunicaciones de la Asociacion Paleontologica Argentina; 2023

Universidad Nacional de Rio Negro

Several remains of fossil eggs and eggshells assigned to dinosaurs have been found in Argentina in the last decades, being most of them assignable to titanosaur sauropods (Megaloolithidae and Faveoloolithidae oofamilies), few of them to birds and just two cases of non-avian theropod, corresponding to alvarezsaurid eggs and eggshells belonging to Arriagadoolithidae oofamily. In this communication, we present the first theropod eggs recorded from La Invernada locality. The material consists in two partial eggs and several fragments of eggsshells (MAU-Pv-LI-608, 609 and 610). The most complete egg (MAU-Pv-LI-609) has a length axis of 10,62cm ± 0,01, while the short axis (equatorial conserved) diameter is 6,88cm ± 0,01, while the compressed ecuatorial diameter is 5,91cm. The eggs are oval in shape and symmetrical in profile, with both poles having the same curvature. Both eggs were found in situ, with their major axis parallel to the ground. The external ornamentation is linearituberculated which is aligned with the long axis of the egg and it changes near the pole, when its turns in ramotuberculate. The volume of egg was estimated (in MAU-Pv-LI- 609) is 225.98ml. The shell thickness average is 0.79mm. The eggshell is composed of two layers: an inner mammillary layer and an outer prismatic layer. The ratio of the thickness of the mammillary layer to prismatic layer is approximately 1:2. Under SEM we observed in the prismatic layer parts with squamatic ultrastructure and vertical crystals which form the main prismatic layer. La Invernada eggs size is similar to Elongatoolithus excellens (10cm x 4cm). The ornamentation is similar to the alvarezsaurid eggs from Río Negro province. The ratio between ML:PL (1:2) similar to Subtioolithus kachchhensis and Tipoolithus achloujensis. The thickness of the eggshells of Trigonoolithus amoe have a wide range from 0.33mm to 1.04mm, in which our material fit. Spheruprismatoolithus condensus also fit in their thickness range 0.66-0.94mm. The squamatic texture of the prismatic layer is also present in Continuoolithus canadensis and Arriagadoolithus patagoniensis. The presence of shells with two layers distinguishes MAU-Pv-LI-608, 609 and 610 from alvarezsaurid eggs, which have three layers. A preliminary cladistic analysis places eggs from La Invernada most closely related to Prismatoolithids from the Two Medicine Formation. The assignment of these eggs to Prismatoolithidae would indicate that they correspond to a non-alvarezsaurid theropod group. In this scenario, the possibility that they belong to abelisaurids or megaraptorids is the most plausible, since both clades have been previously reported in the area. However, the possibility that they belong to some type of ornithopod cannot be ruled out, a clade also recorded in the area.Proyect funded by CONICET PIP 2021-2023 11220200101108CO (AHM), AGENCIA I+D+i PICT 2021-00024 (AHM), PICT 2021-00513 (LSF)