a 40-degree angle; similar to Baryonyx, where it enclosed 35 degrees. Unlike in Baryonyx, Irritators lacrimal did not form a bony horn core. The prefrontal bones were large and sturdy, while the thinner bones, situated behind them, were smooth and concave on top; both of these bones formed the upper rim of the orbit. A thin sagittal crest, constructed from the elongate nasal bones, extended along the skull midline before stopping just above the eye in a slightly flattened bulge. Although the complete shape and height of this structure is unknown in Irritator, these head crests were commonplace in spinosaurids, having possibly served a display function when the animal was alive. The preserved part of Irritators crest is deepest above the antorbital fenestra and lacks the vertical ridges seen in the crest of Spinosaurus. Like others in its family, Irritator possessed a long and bony structure on the roof of its mouth called a secondary palate, separating the oral from the nasal cavity. This is a feature observed in extant crocodilians, but absent in most theropod dinosaurs. Also like its relatives, Irritator had two additional openings on the skull roof (called the postnasal fenestrae) as well as long and only partially diverging (bony extensions connecting the braincase with the palate). The back of the lower jaw was deep, its rear upper surface consisting mainly of the large bone, which with the shallower bone below it. The , a sideways-facing opening in the lower jaw, was oval and comparatively large. The (tooth-bearing bone of the mandible) is unknown in Irritator, save for a possible remnant at the front of the surangular. Irritator challengeris holotype is unique in that it is one of the few non-avian (or non-bird) dinosaur fossils found with a preserved stapes. Irritator had straight or only faintly recurved conical teeth, bearing sharply defined but unserrated edges. Flutes (lengthwise ridges) were present on its tooth crowns, a common dental trait among spinosaurids. Both sides of Irritators teeth were fluted, as in Spinosaurus, whereas Baryonyx exhibited them only on the lingual (inward facing) side of its teeth. Irritators teeth were circular in cross section, as opposed to the laterally flattened condition of most theropod teeth. The enamel (first layer of the teeth) was thin, with a finely wrinkled texture also observed in Baryonyx. Both of Irritators maxillae preserve nine teeth, although the left maxilla's tooth crowns are more intact, and