Majungasaurus (/məˌdʒʌŋɡəˈsɔrəs/; "Mahajanga lizard") is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period. The genus contains a single species, Majungasaurus crenatissimus. This dinosaur was briefly called Majungatholus, a name which is now considered a junior synonym of Majungasaurus.
Like other abelisaurids, Majungasaurus was a bipedal predator with a short snout. Although the forelimbs are not completely known, they were very short, while the hindlimbs were longer and very stocky. It can be distinguished from other abelisaurids by its wider skull, the very rough texture and thickened bone on the top of its snout, and the single rounded horn on the roof of its skull, which was originally mistaken for the dome of a pachycephalosaur. It also had more teeth in both upper and lower jaws than most abelisaurids.
Known from several well-preserved skulls and abundant skeletal material, Majungasaurus has recently become one of the best-studied theropod dinosaurs from the Southern Hemisphere. It appears to be most closely related to abelisaurids from India rather than South America or continental Africa, a fact that has important biogeographical implications. Majungasaurus was the apex predator in its ecosystem, mainly preying on sauropods like Rapetosaurus, and is also one of the few dinosaurs for which there is direct evidence of cannibalism.