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Last updated on April 19, 2014 at 21:20 EDT

Majungasaurus

Majungasaurus, meaning “Mahajanga lizard,” is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Period of what is now Madagascar (70 to 65.5 million years ago). The type species is M. crenatissimus.

Majungasaurus was first described by French paleontologist Charles Depéret in 1896 from a fossil that included two teeth, a claw, and some vertebrae discovered along the Betsiboka River by a French army officer. Depéret referred to these fossils as belonging to Megalosaurus, which at the time was a wastebasket taxon containing numerous other large theropod. He later reassigned the specimen to the North American genus Dryptosaurus, another poorly known category.

Over the next hundred years numerous fragments were found from the Mahajanga Province in northwestern Madagascar, many of which were donated to the Muséum National d’Histoire Naturelle (National Museum of Natural History) in Paris.

In 1955, René Lavocat described theropod teeth fossils found in the Maevarano Formation in the same region where the original material was found. The teeth matched those first described by Depéret, but the jawbone was very different from both Megalosaurus and Dryptosaurus. Lavocat renamed the genus Majungasaurus.

In 1993, scientists from the State University of New York at Stony Brook and the University of Antananarivo began the Mahajanga Basin Project, a series of expeditions to examine the fossils and geology of the Late Cretaceous sediments near the village of Berivotra, in the Mahajanga Province. The first study turned up hundreds of theropod teeth identical to those of Majungasaurus. Seven more expeditions to the region turned up thousands of fossils, many of which belonged to new species to science.

Further fieldwork has turned up fossils of possible Majungasaurus in 1996, 2003 and 2005. The latter dates still await official descriptions.

Majungasaurus was a medium-sized bipedal predator measuring 20 to 23 feet long, including its tail. Some remains have been found of individuals that may have been up to 26 feet long. The average weight of an adult was more than 2,400 pounds, with some weighing up to 3,300 pounds.

This bipedal abelisaurid had very short forelimbs and longer, stocky hindlimbs. It is 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. However, it appears to be more closely related to abelisaurids from India rather than South America of continental Africa. Majungasaurus would have been the apex predator in its ecosystem, mainly preying on sauropods. It is also one of the few dinosaurs for which there is direct evidence of cannibalism.

The skull of Majungasaurus is exceptionally well-known compared to most theropod. Like other abelisaurid skulls, its length was proportionally short for its height. Large individuals had a skull that measured 24 to 28 inches long. The front-most upper jaw bone was also typical of abelisaurids. However, the skull of Majungasaurus was much wider than other abelisaurids. All abelisaurids had a rough, sculptured texture on the outside faces of the skull bones, and Majungasaurus was no exception; the nasal bones proved most so, which were extremely thick and fused together, with a low central ridge running along half of the bone closest to the nostrils. There was a distinctive dome-like horn protruding from the fused frontal bones on top of the skull as well.

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 17 teeth in both the upper jaw and the lower jaw, more than in any other abelisaurid except Rugops.

Majungasaurus had a long tail that balanced out the head and torso, placing the center of gravity on the hips. It had a very strong, muscular neck. The upper arm bone was short and curved, and it had short forelimbs with four extremely reduced digits, with two very short external fingers and no claws. The finger bones were fused together, indicating the hand would have been immobile.

The hindlimbs were stocky and short compared to body length. The lower leg bone was relatively short as well, with a prominent crest on the knee. The ankle bones were also fused together, and the feet bore three functional digits, with a smaller first digit that did not contact the ground.

It has been theorized, based on Majungasaurus’ skull anatomy, that this abelisaurid dinosaur used a bite and hold feeding strategy. Its short and broad snout allowed it to bite once and hold onto its prey until subdued. Other parts of Majungasaurus’ anatomy may support the bite-and-hold theory as well. The neck was strengthened, with robust vertebrae, interlocking ribs and ossified tendons, as well as reinforced muscle attachment sites on the vertebrae and back of the skull. These muscles would have been able to hold the head steady while prey struggles.

The lower jaw also had a high degree of flexibility, an adaptation to prevent fracture when holding onto a struggling prey animal. The front teeth of the jaw were more robust than the rest, to provide an anchor point for the bite, while the low crown height of teeth prevented them from breaking off during a struggle. Majungasaurus also had teeth curved on the front edge but straighter on the back (cutting) edge. This structure may have served to prevent slicing, holding the teeth in place when biting.

Majungasaurus was the largest predator in its environment and perhaps specialized on hunting sauropods. Adaptations to strengthen the head and neck for a bite-and-hold type of attack might have been very useful against sauropods, which would have been tremendously powerful animals. The hindlimbs of Majungasaurus, which were short and stocky, as opposed to the longer and more slender legs of most other theropod, would have had no trouble keeping up with slow-moving sauropods.

Majungasaurus’ tooth marks on Rapetosaurus bones confirm that it at least fed on sauropods, whether or not it actually killed them.

Majungasaurus