Bone microstructure and diagenesis of saurischian dinosaurs from the Upper Cretaceous (Neuquén Group), Argentina

Elena Previtera

doi:10.5027/andgeov44n1-a03

Abstract

The Neuquén Basin in northwestern Patagonia, Argentina, holds the most important record of Cretaceous dinosaurs in South America.The Neuquén Group (Upper Cretaceous) is the richest dinosaur-bearing unit of the basin. It comprises the Río Limay, the Río Neuquén and the Río Colorado subgroups. In this study, dinosaur remains from the Río Neuquén and the Río Colorado subgroups outcropping in Mendoza are examined. In this group, isolated, disarticulated or partially articulated sauropods and theropods are abundant. However, little is known about the diagenetic history of fossil assemblages. In southern Mendoza, three fossiliferous sites were found in the areas of Paso de las Bardas (Quebrada Norte) and Cerro Guillermo (CG1, CG2). This study aims to add to the knowledge of diagenetic processes involving dinosaur remains from the Neuquén Group, as well as their relation to the depositional environment. Histologic features and diagenetic processes of dinosaur bones were analyzed through thin sections in order to interpret the degree of taphonomic alteration. The fossil-diagenetic processes inferred include substitution, fracturing, plastic deformation and different permineralization events. Combined analyses through X-ray diffractometry (XRD) and petrographic studies reveal the substitution of hydroxyapatite by francolite. The presence of fluorine -in one of the cases- suggests a link between the elemental composition and depositional environments: floodplain and fluvial channel. Permineralization stages include infilling of vascular canals, trabeculae and fractures with iron oxides and iron carbonate minerals during the burial history. This contribution represents an integral approach to the study of Cretaceous dinosaurs for assessing the diagenetic changes in the bone microstructure and the differential preservation of fossil remains in fluvial environments.

Highlights

The Neuquén Basin, located in the northwestern Patagonia, Argentina, bears the most important record of Cretaceous dinosaurs in South America
This study aims to add to the knowledge of diagenetic processes involving dinosaur remains from the Neuquén Group, as well as their relation to the depositional environment
These processes are the result of differences in burial depth, temperature and geostatic pressure suffered by the fossils in each burial environment

Summary

Introduction

The Neuquén Basin, located in the northwestern Patagonia, Argentina, bears the most important record of Cretaceous dinosaurs in South America. Most dinosaur species from Argentina have been found in Upper Cretaceous strata of the Neuquén Group, northern Patagonia These findings comprise numerous sauropods and theropods and have significance from both systematic and phylogenetic viewpoints (e.g., Bonaparte, 1991; Novas, 1996; Novas, 1997; Novas and Puerta, 1997; Salgado et al, 1997; Powell, 2003; González Riga, 2003; Wilson, 2002; Calvo and González Riga, 2003; Calvo et al, 2004; Curry Rogers, 2005; Coria and Currie, 2006; Calvo et al, 2007; González Riga et al, 2008; González Riga et al, 2009). Theropod bones of Aerosteon riocoloradensis (Sereno et al, 2008) were collected in the same area

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