site of discovery is uncertain, the specimen most probably stems from the Romualdo Formation (previously designated the Romualdo Member of the then Santana Formation). This assignment was confirmed by microfossils of the ostracod Pattersoncypris, and fish scales from the ichthyodectid Cladocyclus, both found in the Romualdo Formation. Questioning of local fossil dealers hinted at a locality near the village of Buxexé close to Santana Do Cariri at the flank of the Chapada do Araripe, at a height of approximately . Since the Romualdo Formation is indeed exposed there, and the matrix encasing the holotype has the same color and texture as those rocks, this locality can be regarded as the probable site of the discovery of the fossil. Irritator challengeri was the first dinosaur described from the Romualdo Formation, and its holotype specimen represents the most completely preserved spinosaurid skull known. Synonymy with Angaturama Angaturama limai, another spinosaurid from the same time and place as Irritator challengeri, was described by the Brazilian paleontologists Alexander W. A. Kellner and Diogenes de Almeida Campos in February 1996. Kept today under specimen number USP GP/2T-5 at the University of São Paulo, the holotype specimen consists of an isolated snout tip from the Romualdo Formation. It was extracted from a calcareous nodule using a technique originally developed for pterosaur fossils. The generic name is in reference to Angaturama, a protective spirit in the aboriginal Tupi Indian culture of Brazil. The specific name honors the late Brazilian paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991. In 1997, British paleontologists Alan J. Charig and Angela C. Milner considered Angaturama a likely junior synonym of Irritator, noting that both genera had retracted nostrils, long jaws, and characteristic spinosaurid dentition. Paul Sereno and colleagues in 1998 agreed with this possibility, and additionally observed that the holotype of Angaturama seems to complete that of Irritator (meaning that they could belong to the same specimen). Authors including Éric Buffetaut and Mohamed Ouaja in 2002, Cristiano Dal Sasso and colleagues in 2005, Tor G. Bertin in 2010, Darren Naish in 2013, and Madani Benyoucef and colleagues in 2015 supported this conclusion. In their redescription of Irritator, Sues and colleagues pointed out that both holotypes are equally as narrow, and share transversely round teeth with defined yet unserrated edges. They also noted that a sagittal crest on Angaturamas premaxillae may correspond with that of Irritators nasal bones.