Majungasaurus

***Majungasaurus*** (/məˌdʒʌŋɡəˈsɔrəs/ mah-JUNG-gə-SOR-əs; "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. Only one species (*Majungasaurus crenatissimus*) has been identified. 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 which 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 measured 6–7 meters (20–23 ft) in length, including its tail.[1] Fragmentary remains of larger individuals indicate that some adults reached lengths of more than 8 meters (26 ft).[2] Sampson and Witmer estimated an average weight for an adult *Majungasaurus* of 1130 kilograms (2400 lb).[2] The specimen they based it on (FMNH PR 2100) was not the largest one discovered. Larger specimen suggest that *Majungasaurus crenatissimus* could have reached similar sizes to its relative *Carnotaurus*,[2] which has been estimated to weigh 1500 kilograms (3300 lb).

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.[5] 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, with only two very short external fingers and no claws.[6] The hand and finger bones of *Majungasaurus*, like other carnotaurines, 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.[7]

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.

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.[2] The teeth were typical of abelisaurids in having short crowns, although *Majungasaurus* bore 17 teeth in both the maxilla of the upper jaw and the dentary of the lower jaw, more than in any other abelisaurid except *Rugops*.

## Classifications and Systematics

*Majungasaurus* is classified as a member of the theropod clade Abelisauridae, which is considered a family in Linnaean taxonomy. Along with the family Noasauridae, abelisaurids are included in the superfamily Abelisauroidea, which is in turn a subdivision of the infraorder Ceratosauria.[1][9] Abelisaurids are known for their tall skulls with blunt snouts, extensive sculpturing on the outer surfaces of the facial bones (convergent with carcharodontosaurids), very reduced (atrophied) forelimbs (convergent with tyrannosaurids), and stocky hindlimb proportions, among other features.[10]

As with many dinosaur families, the systematics (evolutionary relationships) within the family Abelisauridae are confused. Several cladistic studies have indicated that *Majungasaurus* shares a close relationship with *Carnotaurus* from South America,[9][10] while others were unable to firmly place it in the phylogeny.[11] The most recent analysis, using the most complete information, instead recovered *Majungasaurus* in a clade with *Rajasaurus* and *Indosaurus* from India, but excluding South American genera like *Carnotaurus*, *Ilokelesia*, *Ekrixinatosaurus*, *Aucasaurus* and *Abelisaurus*, as well as *Rugops* from mainland Africa. This leaves open the possibility of separate clades of abelisaurids in western and eastern Gondwana.[1] Detailed description of known abelisaurids like *Aucasaurus* as well as future discoveries and analyses may help to resolve the phylogenetic picture.