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.

These included two teeth, a claw, and some vertebrae discovered along the Betsiboka River by a French army officer and deposited in the collection of what is now the Université Claude Bernard Lyon 1.

Depéret referred these fossils to the genus Megalosaurus, which at the time was a wastebasket taxon containing any number of unrelated large theropods, as the new species M.

[1] This name is derived from the Latin word crenatus ("notched") and the suffix -issimus ("most"), in reference to the numerous serrations on both front and rear edges of the teeth.

[3] Numerous fragmentary remains from Mahajanga Province in northwestern Madagascar were recovered by French collectors over the next 100 years, many of which were deposited in the Muséum National d'Histoire Naturelle in Paris.

Based on this dentary, Lavocat created the new genus Majungasaurus, using an older spelling of Mahajanga as well as the Greek word σαυρος sauros (meaning "lizard").

[7] Further fieldwork over the next decade turned up a series of less complete skulls, as well as dozens of partial skeletons of individuals ranging from juveniles to adults.

[2] This fieldwork culminated in a 2007 monograph consisting of seven scientific papers on all aspects of the animal's biology, published in the Society of Vertebrate Paleontology Memoirs.

[2][11][12][13] 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 tall premaxilla (frontmost upper jaw bone), which made the tip of the snout very blunt, was also typical of the family.

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.

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.

[17] 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, possibly with no claws.

Several cladistic studies have indicated that Majungasaurus shares a close relationship with Carnotaurus from South America,[20][21] while others were unable to firmly place it in the phylogeny.

[22] 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.

[13] Scientists have suggested that the unique skull shape of Majungasaurus and other abelisaurids indicate different predatory habits than other theropods.

[24] In comparison to modern mammalian predators, most theropods may have used a strategy similar in some ways to that of long- and narrow-snouted canids, with the delivery of many bites weakening the prey animal.

[25] Abelisaurids, especially Majungasaurus, may instead have been adapted for a feeding strategy more similar to modern felids, with short and broad snouts, that bite once and hold on until the prey is subdued.

[29] Scientists have reconstructed the respiratory system of Majungasaurus based on a superbly preserved series of vertebrae (UA 8678) recovered from the Maevarano Formation.

[30] Computed tomography, also known as CT scanning, of a complete Majungasaurus skull (FMNH PR 2100) allowed a rough reconstruction of its brain and inner ear structure.

Overall, the brain was very small relative to body size, but otherwise similar to many other non-coelurosaurian theropods, with a very conservative form closer to modern crocodilians than to birds.

This suggests that Majungasaurus and other abelisaurids like Indosaurus, which also had a small flocculus, did not rely on quick head movements to sight and capture prey.

The lateral canal is also significantly longer in Majungasaurus than in its more basal relative Ceratosaurus, indicating a greater sensitivity to side-to-side motions of the head.

One explanation for this pathology is severe physical trauma resulting in the loss of the tail tip, followed by osteomyelitis (infection) of the last remaining vertebrae.

[31] The small number of specimens preserved with pathologies in Majungasaurus suggest that the multitude of injuries that occurred were obtained over the course of the lives of the individuals studied.

Based on studies of the lines of arrested growth in several bones, it was found that Majungasaurus took twenty years to reach maturity, which may have been a result of the harsh environment in which it lived.

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).

[38] 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.

[44] 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.