Registro fósil de la Formación Bajo de la Carpa (Cretácico superior) en el Área natural protegida de Paso Córdoba (Río Negro, Argentina): implicancias paleoecológicas y paleobiológicas e inferencias paleoambientales

Abstract

The Natural Protected Area "Paso Córdoba" (ANPPC) is located at 15 km from General Roca city, province of Río Negro, Argentina, and has aroused scientific interest since the beginning of the last century, with the discovery of the first dinosaur in the area, Antarctosaurus wichmannianus von Huene, 1929. The Mesozoic of ANPPC is represented by three formations belonging to the Neuquén Basin: Bajo de la Carpa (Santonian), Anacleto (middle-lower Campanian), and Allen (upper Campanian-lower Maastrichtian). The Cretaceous continental tetrapod record of these units is notable, highlighting the herpetological repertoire of Bajo de la Carpa Formation, particularly in the region known as “Cañadón de los Cocodrilos” (CDC). To date, this record consists of theropods, snakes, and crocodiles. Despite the previous knowledge, there are no integrative contributions that seek to understand the composition and variability in space, time, and environmental context of this paleofauna. This final degree thesis (TFG) intends to review the vertebrate paleofauna registered at the CDC with an integrating and multidisciplinary perspective, which main objective is to contribut to the knowledge of the paleoecological, paleobiological, and paleoenvironmental context of this area. The components of the paleofauna and the paleoedaphological characteristics of the CDC deposits represent a very interesting case. First of all, the abundance and diversity of the fossil remains is remarkable, particularly the fossil traces of roots and complex structures identified as burrows. One type of them resembles the specimens of the ichnogenus Camborygma isp., associated with freshwater crayfish, while the others correspond to specimens of Daimonelix isp., identified as burrows used for nesting or reproduction of small mammals and reptiles. These ichnotaxons, as well as the burrows, reflect specific behaviors related to the characteristics of the substrate and the anatomy and lifestyle of their producers. To give rise to a population of infaunal decapods that build galleries of moderate complexity associated with plants, such as the CDC specimens, it is inferred close distance to a channel with a high availability of nutrients and oxygen in the substrate and underground. On the other hand, the abundance and distribution of the specimens assigned to Daimonelix isp. allows us to infer that the producers had a fossorial behavior and were gregarious. Based on the topological and architectural attributes of the CDC rhizoliths, two different types of preservation are distinguished: rhizohalos and rhizocretions. The rhizohalos of the lower levels of the paleo-edaphosequence allows us to infer poorly drained paleosols with seasonal saturation, while the levels near the middle section, which contain the highest density of long roots, suggest a seasonally dry environment. Calcareous horizons with a high density of rhizoconcretions indicate an environment with high density of vegetation adapted to drained soils, but with a seasonally high water table or the influence of ephemeral flows. In contrast, the bone remains found at the CDC are poorly preserved, fragmentary, and scarce, most of them concentrated on a single surface. The exception is the materials identified in this work as Notosuchus terrestris Woodward, 1896 from the upper portion of the CDC and two other fragmentary remains identified as Sauropoda indet.