Análisis Tafonómico de un Dinosaurio Pico de Pato (Familia Hadrosauridae) de la Formación Cerro del Pueblo (Cretácico Superior, Campaniano), Coahuila: Implicaciones Preservacionales y Paleoecológicas

The Cerro del Pueblo Formation is worldwide recognized due to the high abundance and diversity of its fossil material. Most vertebrate studies (dinosaurs, turtles, crocodiles and fish) that have been performed in this formation are of taxonomic nature. Particularly in the case of dinosaurs, taphonomic analyses have not been conducted which generates a great limitation in understanding the biostratinomic processes and fossildiagenesis stages that are present within this lithostratigraphic unit. In this research, we identified and interpreted the taphonomic signature of a dinosaur belonging to the family Hadrosauridae collected in this formation. In addition, we performed a facies analysis of the outcrop in order to extend the stratigraphic and paleoenvironmental knowledge of the Cerro del Pueblo Formation within the study area at General Cepeda Municipality. The hadrosaur skeleton was mostly disarticulated and it was represented by several skull bones (endocranium, left maxillary, right postorbital, right quadrate and isolated teeth), some vertebrae and ribs, right scapula, both humeri, left ulna and radius, left pubis, left femur, both tibiae and fibulae, and a pair of metatarsals. For taphonomic evaluation, the following parameters were considered: (1) Bone representativeness; (2) Disarticulation degree; (3) Weathering; (4) Teeth marks; (5) Breakage; (6) Abrasion; and (7) Hydraulic equivalence. The weathering degree of the specimen was low (stage 1), as only few desiccation marks parallel to bone structure were observed in some ribs and long bones, which are indicative of a short time of subaerial exposure. Furthermore, a lower abrasion (stage 1) indicates that the hadrosaur experienced a short transport toward its final depositional place; whereas the lack of hydraulic equivalence with the rock matrix, suggests that it was transported as a "water carcass", this coupled with the high disarticulation of the skeleton and the chaotic distribution of the bones inside the fossiliferous bed. The presence of different types of teeth marks suggests the acting of scavengers on the specimen. Also, an almost vertical position of the bones suggests that some of them were trampled by other animals. The fractures present on the fossil material were produced in two different stages, during biostratinomy (longitudinal and spiral fractures) and when the fossildiagenesis took place (transversal fractures). Finally, the facies analysis indicates that the final depositional environment corresponded to a lagoonal system interconnected with a proximal marsh.