Majungasaurus (“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, 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 and this dinosaur was briefly called Majungatholus, a name which is now considered a junior synonym of Majungasaurus.
Majungasaurus was a medium-sized theropod that typically measured 6–7 meters (19.7–23.0 ft) in length, including its tail. Fragmentary remains of larger individuals indicate that some adults reached lengths of more than 8 meters (26.2 ft). An allometric study in 2016 found it to be 5.6 meters (18.4 ft) long. Sampson and Witmer estimated an average weight for an adult Majungasaurus of 1,100 kilograms (2,400 lb). The specimen they based it on (FMNH PR 2100) was not the largest one discovered. Larger specimens of Majungasaurus crenatissimus could have been similar in size to its relative Carnotaurus, which has been estimated to weigh 1,500 kilograms (3,300 lb).
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.
The postcranial skeleton of Majungasaurus closely resembles those of Carnotaurus and Aucasaurus, the only other abelisaurid genera for which complete skeletal material is known. Majungasaurus was bipedal, with a long tail to balance out the head and torso, putting the center of gravity over the hips. Although the cervical (neck) vertebrae had numerous cavities and excavations (pleurocoels) to reduce their weight, they were robust, with exaggerated muscle attachment sites and ribs that interlocked for strength. Ossified tendons attached to the cervical ribs, giving them a forked appearance, as seen in Carnotaurus. All of these features resulted in a very strong and muscular neck. Uniquely, the cervical ribs of Majungasaurus had long depressions along the sides for weight reduction. The humerus (upper arm bone) was short and curved, closely resembling those of Aucasaurus and Carnotaurus. Also like related dinosaurs, Majungasaurus had very short forelimbs with four extremely reduced digits, first reported with only two very short external fingers and no claws. The hand and finger bones of Majungasaurus, like other majungasaurines, lacked the characteristic pits and grooves where claws and tendons would normally attach, and its finger bones were fused together, indicating that the hand was immobile. In 2012, a better specimen was described, showing that the lower arm was robust, though short, and that the hand contained four metatarsals and four, probably inflexible and very reduced, fingers, with small claws on the second and third finger. The phalanx formula was 1-2-2-1-0.
Like other abelisaurids, the hindlimbs were stocky and short compared to body length. The tibia (lower leg bone) of Majungasaurus was even stockier than that of its relative Carnotaurus, with a prominent crest on the knee. The astragalus and calcaneum (ankle bones) were fused together, and the feet bore three functional digits, with a smaller first digit that did not contact the ground.
Majungasaurus was one of the last dinosaurs to walk earth, replaced its teeth as fast as sharks.
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