Both "Irritator" and "Angaturama" belong to the Spinosaurinae subfamily. In 1996, the specimen became the holotype of the type species Irritator challengeri. Dinosaur fauna includes theropods like "Irritator", "Santanaraptor," "Mirischia," and an indeterminate unenlagiine dromaeosaur. "Irritator" shared with crocodilians a stiff secondary palate and reduced antorbital fenestrae. Nevertheless, "Irritator" also bore unserrated teeth, a trait associated with spinosaurines. Even by maximal size estimates, "Irritator" was smaller than other known spinosaurids. "Irritator" had been mistaken initially for a pterosaur, and later a maniraptoran dinosaur.