The first theropod dinosaur (Coelurosauria, Theropoda) from the base of the Romualdo Formation (Albian), Araripe Basin, Northeast Brazil

Abstract

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

Osteohistology and microanatomy of a new specimen of Cearachelys placidoi (Testudines: Pleurodira) a side‐necked turtle from the lower Cretaceous of Brazil

“…Cearachelys placidoi Gaffney, Campos and Hirayama, 2001 was a marine bothremydid found in the Aptian levels of Araripe Basin in northeastern Brazil (Arai & Assine, 2020). This basin is worldwide famous for the well‐preserved fossil vertebrates (Sayão et al, 2020), among which five turtle species were recognised so far (Gaffney, Tong, & Meylan, 2006; Gaffney, Campos, & Hirayama, 2001; Hirayama, 1998; Lapparent de Broin, 2000b; Price, 1973). Within Brazilian bothremydids, Cearachelys is the most common taxon, appearing in the geological record with a higher number of specimens reported.…”

Digging deeper into colonial palaeontological practices in modern day Mexico and Brazil

“…The Palaeontology Museum 'Plácido Cidade Nuvens' at Santana do Cariri, which contains thousands of fossils from the Araripe Basin, was founded in 1985-presumably before most of the Araripe Basin fossils included in this study were collected. Currently, local researchers associated with this museum coordinate controlled excavations in the region [156][157][158], and several scientific publications have been produced based on these materials [159][160][161][162][163][164][165] (see more publications in electronic supplementary material, table S2). This museum would be the logical place to store a number of holotypes and other important fossils that are now in foreign collections.…”

There are rudists in Brazil! Derived examples of cf. Amphitriscoelus Harris and Hodson, 1922, in the Araripe Basin, north-east Brazil: Implications for dating of the fossil Lagerstätten of the Santana and Crato formations

“…e.g. Arai and Assine, 2020;Sayão et al, 2020) of the Araripe Basin in north-east Brazil is extremely well known for a stratigraphic unit, the Romualdo Member, rich in early diagenetic concretions containing exceptionally well preserved vertebrate fossils (Martill, 1988;Maisey, 1991). The contained fossils are commonly fully articulated, often preserved in three-dimensions and frequently preserve soft tissues (Martill, 1988;Brito et al, 2010;Maldanis et al, 2016) and gut contents (Wilby and Martill, 1992).…”