The Romualdo Formation (Araripe Basin) is worldwide known for the large number of well-preserved fossils but the dinosaur record is rather scarce. Here we describe a new coelurosaur, which is the first tetrapod recovered from the basal layers of this stratigraphic unit that consist of dark shales. Aratasaurus museunacionali gen. et sp. nov. is known by an incomplete but articulated right hind limb with the distal portion of the femur, proximal half of tibia and incomplete pes. The new species differs from other coelurosaurs by a medial fossa in the tibia and digits II, III and IV being symmetric. The phylogenetic analysis recovered Aratasaurus museunacionali closely related to Zuolong salleei, forming a basal coelurosaur lineage. The paleohistology indicate that the specimen is a juvenile, with an estimated body length around 3.12 m. The new taxon represents the first occurrence of basal coelurosaurians in the Araripe Basin and suggests a widespread distribution of this group during the Lower Cretaceous. The dinosaur record in Brazil is still quite meager compared to the potential of the country 1,2. So far, most specimens were recovered from the Bauru Group, including non-avian theropods 3,4,5,6,7. The latter are less numerous in these deposits than other reptiles 8 , leading to several discussions, including niche partitioning 7. The limited amount of theropod material is not exclusive of Brazil 9. Among the regions where such reptiles are found in the country is the Araripe Basin 10. This tectonic structure is worldwide known for the well preserved and diverse fossil biota 11,12,13,14. The most fossiliferous units are the Lower Cretaceous Crato and Romualdo formations, comprising the majority of fossil vertebrates of this basin 14. As has been reported several times, the most common tetrapod in both units are pterosaurs 15 , while others tend to be rare 16,17,18. Until now all non-avian dinosaur from the Araripe Basin came exclusively from the Romualdo Formation and are represented by the spinosaurids Irritator challengeri 19 and Angaturama limai 1 and the non-avian coelurosaurs Santanaraptor placidus 20,21 and Mirischia assymetrica 22. All were preserved in the level of carbonate concretions from the upper portion of this stratigraphic unit 14,23,24. Here we describe a new theropod dinosaur from the Romualdo Formation that was collected in the lower section. The fossil is preserved in a slab of dark shale, housed at the Museu de Paleontologia Plácido Cidade