Majungasaurus (/məˌdʒʌŋɡəˈsɔːrəs/; lit. 'Mahajanga lizard') is a genus of abelisauridtheropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period, making it one of the last-known non-avian dinosaurs that went extinct during the Cretaceous–Paleogene extinction event. The genus contains a single species, Majungasaurus crenatissimus. This dinosaur is also called Majungatholus, a name which is 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 hind limbs 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.
The genus is one of the first abelisaurs to be discovered, first being found in 1896 (although it was thought to be a species of Megalosaurus) and being named in 1955. 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.
Description[]
Majungasaurus was a medium-sized theropod that typically reached 5.6–7 m (18–23 ft) in length and weighed 750–1,100 kg (1,650–2,430 lbs).Fragmentary remains of larger individuals indicate that some adults could have been similar in size to its relative Carnotaurus, possibly exceeding 8 m (26 ft) in length.
The skull of Majungasaurus is exceptionally well known compared to most theropods and generally similar to that of other abelisaurids. Like other abelisaurid skulls, its length was proportionally short for its height, although not as short as in Carnotaurus. The skulls of large individuals measured 60–70 centimeters (24–28 in) long. The tall premaxilla (frontmost upper jaw bone), which made the tip of the snout very blunt, was also typical of the family. However, the skull of Majungasaurus was markedly wider than in other abelisaurids. All abelisaurids had a rough, sculptured texture on the outside faces of the skull bones, and Majungasaurus was no exception. This was carried to an extreme on the nasal bones of Majungasaurus, which were extremely thick and fused together, with a low central ridge running along the half of the bone closest to the nostrils. A distinctive dome-like horn protruded from the fused frontal bones on top of the skull as well. In life, these structures would have been covered with some sort of integument, possibly made of keratin. Computed tomography (CT scanning) of the skull shows that both the nasal structure and the frontal horn contained hollow sinus cavities, perhaps to reduce weight. The teeth were typical of abelisaurids in having short crowns, although Majungasaurus bore seventeen teeth in both the maxilla of the upper jaw and the dentary of the lower jaw, more than in any other abelisaurid except Rugops.
Madagascar, Maastrichtian Stage of the Late Cretaceous, 70-66 Million Years Ago[]
All specimens of Majungasaurus have been recovered from the Maevarano Formation in the Mahajanga Province in northwestern Madagascar. Most of these, including all of the most complete material, came from the Anembalemba Member, although Majungasaurus teeth have also been found in the underlying Masorobe Member and the overlying Miadana Member. While these sediments have not been dated radiometrically, evidence from biostratigraphy and paleomagnetism suggest that they were deposited during the Maastrichtian stage, which lasted from 70 to 66 Ma (million years ago). Majungasaurus teeth are found up until the very end of the Maastrichtian, when all non-avian dinosaurs became extinct.
Then as now, Madagascar was an island, having separated from the Indian subcontinent less than 20 million years earlier. It was drifting northwards but still 10 to 15 degrees more southerly in latitude than it is today. The prevailing climate of the time was semi-arid, with pronounced seasonality in temperature and rainfall. Majungasaurus inhabited a coastal flood plain cut by many sandy river channels.Strong geological evidence suggests the occurrence of periodic debris flowsthrough these channels at the beginning of the wet season, burying the carcasses of organisms killed during the preceding dry season and providing for their exceptional preservation as fossils. Sea levels in the area were rising throughout the Maastrichtian, and would continue to do so into the Paleocene Epoch, so Majungasaurus may have roamed coastal environments like tidal flats as well. The neighboring Berivotra Formation represents the contemporaneous marineenvironment.
Besides Majungasaurus, fossil taxa recovered from the Maevarano include fish, frogs, lizards, snakes, seven distinct species of crocodylomorphs, five or six species of mammals, Vorona and several other birds, the possibly flighted dromaeosaurid Rahonavis, the noasaurid Masiakasaurus and two titanosaurian sauropods, including Rapetosaurus. Majungasaurus was by far the largest carnivore and probably the dominant predator on land, although large crocodylomorphs like Mahajangasuchus and Trematochampsa might have competed with it closer to water.