CONICET | Buscador de Institutos y Recursos Humanos

The Neuquén Basin, located in northwestern Patagonia, Argentina, has the most important record of Cretaceous dinosaurs from South America. Biostratinomic and fossil-diagenetic studies about these vertebrates are scarce since most papers are focus in systematic aspects. Dissarticulated or isolated titanosaur sauropod remains are particularly abundant in the Neuquén Group (Cenomanian-lower Campanian). This indicates that the preservation is conditioned by both the characteristics of the organisms (intrinsic factors) and the sedimentary environments (extrinsic factors). In this context, we focus our study in four main taphonomic aspects: size and behaviour of sauropods, diagenetic features of the sedimentary facies and intervention of the biologic agents. In Mendoza province, we studied three sauropod quarries with different types of preservation: 1) one specimen disarticulated in Quebrada Norte quarry (Malarguesaurus florenciae González Riga et al.), 2) four disarticulated and partially articulated specimens in Arroyo Seco quarry (Mendozasaurus neguyelap González Riga), and 3) one articulated specimen in Cerro Guillermo quarry (unnamed taxon). In the first case, disarticulated bones of Malarguesaurus were preserved in distal floodplain deposits. Biostratinomic processes include a complete disarticulation, absence of preferential orientation, subaerial biodegradation and pre and post-fossilization bone weathering. Fossil-diagenetic processes include a series of permineralization and cementation stages of hematite and calcite. The sedimentary context and the absence of any selection by shape and size, as well as a chaotic spatial distribution, indicate scarce hydraulic transport. The total disarticulation of the carcass can be explained by biologic agents like predators and scavengers. In the second case, an autochthonous-parautochthonous assemblage with 200 articulated and disarticulated bones from Mendozasaurus was preserved in a taphonomic mode named overbank bones assemblages. The main biostratinomic processes include: subaerial biodegradation, disarticulation and necrokynesis, preferential orientation by sporadic water currents (overbank flows), intense brittle and plastic deformation due to lithostatic compression and pre-fossilization bone weathering. Fossil-diagenetic processes comprise permineralization and cementation stages of hematite and calcite. In the third case, an unnamed large titanosaur specimen was discovered in pelitic deposits within floodplain facies with abundant carbonate nodules, trace fossils and paleosols. The specimen includes an incomplete and articulated anterior caudal series and a complete and articulated left pes. The articulated preservation of the specimen without weathering and the sedimentary context suggest the absence of extrinsic factors during the burial history (hydraulic action, biologic intervention). This comparative analysis allows us to recognize different biologic and sedimentary factors that conditioned the preservation of sauropods within the same meandering fluvial system.