O registro icnológico de Sauropoda (dinosauria) da Bacia do Rio do Peixe, Nordeste do Brasil

Abstract

The ichnological study of trackways and footprints associated with sauropod dinosaurs helps to recognize the trackmaker, understand its biomechanics, recover paleoecological aspects and, above all, understand the macroevolution of the group. The Rio do Peixe Basin, located in Northeast Brazil, includes a group of the same name from the Lower Cretaceous (Berriasian-Hauterivian), which has a great abundance of dinosaur ichnofossils, including ornithischian, theropod and sauropod footprints. There are currently 40 formally described ichnosites in the Rio do Peixe Group, twelve of which contain sauropod footprints. This study carried out a survey of ichnosites with sauropod footprints and trackways in Brazil. It was observed that the Brazilian ichnological record of Sauropoda lacks more detailed descriptions and important information for understanding the distribution and diversity of the group. In addition to the survey of ichnosites, a new locality with sauropod footprints was described in the Rio do Peixe Group, in the Sousa Formation. This locality, called 'Sítio Feijão', situated in the municipality of São João do Rio do Peixe-PB, has a well-preserved trackway (SJFE-A) with seven footprints of a large sauropod dinosaur, as well as five other trackways associated with theropods and undetermined tetrapods (SJFE-B to SJFE-F). The SJFE-A trackway, associated with Sauropoda, showed unique morphological characteristics, which allowed the description of a new ichnogenus and ichnospecies. These include rounded pes with the inner margin straighter than the outer, five digits, the last three facing outwards, low heteropodia (approximately 1:2), narrow gauge, a manus with five callosities and the claw of digit I not apparent. These characteristics allowed the interpretation of a Titanosauriformes trackmaker, although it is not possible to specify a less inclusive group. The SJFE-A trackway, to date, is the only record for the Rio do Peixe Basin with a well-preserved manus associated with its corresponding pes, which allows for a more in-depth discussion of the affinity of the trackmaker. This discovery contributes to the understanding of the morphology and evolution of posture and locomotion in early Titanosauriformes, providing evidence that the loss of the phalanges in the manus occurred before the evolution of robust, arched limbs in derived Titanosauriformes