Irritator challengeri is a spinosaurid dinosaur connected to Spinosaurus. It is thought to have lived in the early Cretaceous time, around 110 million years ago. Current estimations indicate a length of 8 meters (26 feet) and a height of 3 meters (9 feet).

It was named by paleontologists Martill, Cruikshank, Frey, and Small & Clarke in 1996. Its only known fossil, a 80cm skull exposed in Brazil, was badly covered by plaster added by the amateurs who exposed it, and required a great deal of work to restore - hence the name. The species name challengeri comes from the nature of Professor Challenger in Arthur Conan Doyle's The Lost World

It is almost certainly synonymous with Angaturama limai, another spinosaurid from the same time and place, whose remains inquisitively seem to complete Irritator's skull, meaning that they could belong to the same specimen.