Majungasaurus
Encyclopedia
Majungasaurus is a genus
of abelisaurid theropod dinosaur
that lived in Madagascar
from 70 to 65.5 million years ago, at the end of the Cretaceous
Period. Only one species
(M. 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 biped
al 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 continent
al 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
.
s (2400 lb
), although the largest animals would have weighed more. Its 8–9 meter (26–30 ft) relative Carnotaurus
has been estimated to weigh 1500 kilograms (3300 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 bone
s 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 bone
s 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 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
.
The postcrania
l 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 rib
s that interlocked for strength. Ossified
tendon
s 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, with only two very short external fingers and no claws. 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.
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.
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
. 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.
As with many dinosaur families, the systematics
(evolution
ary relationships) within the family Abelisauridae are confused. Several cladistic studies have indicated that Majungasaurus shares a close relationship with Carnotaurus from South America, while others were unable to firmly place it in the phylogeny. 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
. Detailed description of known abelisaurids like Aucasaurus as well as future discoveries and analyses may help to resolve the phylogenetic picture.
paleontologist Charles Depéret
described the first theropod remains from northwestern Madagascar in 1896. 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. crenatissimus. 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. Depéret later reassigned the species to the North American genus Dryptosaurus
, another poorly known taxon.
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
. In 1955, René Lavocat
described a theropod dentary with teeth from the Maevarano Formation
in the same region where the original material was found. The teeth matched those first described by Depéret, but the strongly curved jaw bone was very different from both Megalosaurus and Dryptosaurus. Lavocat renamed the genus Majungasaurus, using an older spelling of Mahajanga as well as the Greek
word σαυρος/sauros (meaning "lizard"), and made this jaw bone (MNHN
.MAJ 1) the type specimen. Hans-Dieter Sues
and Philippe Taquet
described a dome-shaped skull fragment (MNHN.MAJ 4) as a new genus of pachycephalosaur (Majungatholus atopus) in 1979. This was the first report of a pachycephalosaur in the Southern Hemisphere.
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 Mahajanga Province. Among these scientists was paleontologist David W. Krause
of Stony Brook. The first expedition turned up hundreds of theropod teeth identical to those of Majungasaurus, some of which were attached to an isolated premaxilla that was described in 1996. The following seven expeditions would turn up tens of thousands of fossils, many of which belonged to species new to science. The Mahajanga Basin Project claims credit for quintupling the known diversity of fossil taxa in the region.
Fieldwork in 1996 turned up a spectacularly complete theropod skull preserved in exquisite detail (FMNH
PR 2100). On top of this skull was a dome-shaped swelling nearly identical to the one described by Sues and Taquet as Majungatholus atopus. Majungatholus was redescribed as an abelisaurid rather than a pachycephalosaur in 1998. Although the name Majungasaurus crenatissimus was older than Majungatholus atopus, the authors judged the type dentary of Majungasaurus too fragmentary to confidently assign to the same species as the skull. 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. Project members also collected hundreds of isolated bones and thousands of shed Majungasaurus teeth. Taken together, these remains represent nearly all the bones of the skeleton, although most of the forelimbs, most of the pelvis
and the tip of the tail are still unknown. 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. The papers are in English
, although each has an abstract
written in Malagasy
. In this volume, the dentary described by Lavocat was re-evaluated and determined to be diagnostic for this species. Therefore, the name Majungatholus was replaced by the older name Majungasaurus. Although the monograph is comprehensive, the editors noted that it describes only material recovered from 1993 through 2001. A significant quantity of specimens, some very complete, were excavated in 2003 and 2005 and await preparation and description in future publications.
itself bore crests on the head. These structures are likely to have played a role in intraspecific competition
, although their exact function within that context is unknown. The hollow cavity inside the frontal horn of Majungasaurus would have weakened the structure and probably precluded its use in direct physical combat, although the horn may have served a display
purpose. While there is variation in the ornamentation of Majungasaurus individuals, there is no evidence for sexual dimorphism
.
(twisting). 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.
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. Majungasaurus had an even broader snout than other abelisaurids, and other aspects of its anatomy may also support the bite-and-hold hypothesis. The neck was strengthened, with robust vertebrae, interlocking ribs and ossified tendons, as well as reinforced muscle attachment sites on the vertebrae and the back of the skull. These muscles would have been able to hold the head steady despite the struggles of its prey. Abelisaurid skulls were also strengthened in many areas by bone mineralized
out of the skin
, creating the characteristic rough texture of the bones. This is particularly true of Majungasaurus, where the nasal bones were fused and thickened for strength. On the other hand, the lower jaw of Majungasaurus sported a large fenestra (opening) on each side, as seen in other ceratosaurs, as well as synovial joint
s between certain bones that allowed a high degree of flexibility in the lower jaw, although not to the extent seen in snake
s. This may have been an adaptation to prevent the fracture of the lower jaw when holding onto a struggling prey animal. The front teeth of the upper jaw were more robust than the rest, to provide an anchor point for the bite, while the low crown height of Majungasaurus teeth prevented them from breaking off during a struggle. Finally, unlike the teeth of Allosaurus
and most other theropods, which were curved on both the front and back, abelisaurids like Majungasaurus had teeth curved on the front edge but straighter on the back (cutting) edge. This structure may have served to prevent slicing, and instead holding the teeth in place when biting.
Majungasaurus was the largest predator in its environment, while the only known large herbivores at the time were sauropods like Rapetosaurus. Scientists have suggested that Majungasaurus, and perhaps other abelisaurids, 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. This hypothesis may also be supported by the hindlegs of Majungasaurus, which were short and stocky, as opposed to the longer and more slender legs of most other theropods. While Majungasaurus would not have moved as fast as other similar-sized theropods, it would have had no trouble keeping up with slow-moving sauropods. The robust hindlimb bones suggest very powerful legs, and their shorter length would have lowered the animal's center of gravity. Thus Majungasaurus may have sacrificed speed for power. Majungasaurus tooth marks on Rapetosaurus bones confirm that it at least fed on these sauropods, whether or not it actually killed them.
Coelophysis
was a cannibal have been recently disproven, leaving Majungasaurus as the only non-avian theropod with confirmed cannibalistic tendencies, although there is some evidence that cannibalism may have occurred in other species as well.
It is unknown if Majungasaurus actively hunted their own kind or only scavenged
their carcasses. However, some researchers have noted that modern Komodo monitors sometimes kill each other when competing for access to carcasses. The lizard
s will then proceed to cannibalize the remains of their rivals, which may suggest similar behavior in Majungasaurus and other theropods.
of Majungasaurus based on a superbly preserved series of vertebrae (UA
8678) recovered from the Maevarano Formation. Most of these vertebrae and some of the ribs contained cavities (pneumatic foramina) that may have resulted from the infiltration of avian
-style lungs and air sacs. In birds, the neck vertebrae and ribs are hollowed out by the cervical air sac, the upper back vertebrae by the lung
, and the lower back and sacral
(hip) vertebrae by the abdominal air sac. Similar features in Majungasaurus vertebrae imply the presence of these air sacs. These air sacs may have allowed for a basic form of avian-style 'flow-through ventilation,' where air flow through the lungs is one-way, so that oxygen
-rich air inhaled from outside the body is never mixed with exhaled air laden with carbon dioxide
. This method of respiration, while complicated, is highly efficient.
The recognition of pneumatic foramina in Majungasaurus, besides providing an understanding of its respiratory biology, also has larger-scale implications for evolutionary biology. The split between the ceratosaur line, which led to Majungasaurus, and the tetanuran
line, to which birds belong, occurred very early in the history of theropods. The avian respiratory system, present in both lines, must therefore have evolved before the split, and well before the evolution of birds themselves. This provides further evidence of the dinosaurian origin of birds.
, 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-coelurosauria
n theropods, with a very conservative form closer to modern crocodilia
ns than to birds. One difference between Majungasaurus and other theropods was its smaller flocculus, a region of the cerebellum
that helps to coordinate movements of the eye
with movements of the head. 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.
Inferences about behavior can also be drawn from examination of the inner ear. The semicircular canals within the inner ear aid in balance, and the lateral semicircular canal is usually parallel to the ground when the animal holds its head in an alert posture. When the skull of Majungasaurus is rotated so that its lateral canal is parallel to the ground, the entire skull is nearly horizontal. This contrasts with many other theropods, where the head was more strongly downturned when in the alert position. 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.
in the bones of Majungasaurus. Scientists examined the remains of at least 21 individuals and discovered four with noticeable pathologies. While pathology had been studied in large tetanuran
theropods like allosaurid
s and tyrannosaurids, this was the first time an abelisauroid had been examined in this manner. No wounds were found on any skull elements, in contrast to tyrannosaurids where sometimes gruesome facial bites were common. One of the specimens was a phalanx
(toe bone) of the foot, which had apparently been broken and subsequently healed.
Most of the pathologies occurred on the vertebrae. For example, a dorsal (back) vertebra from a juvenile animal showed an exostosis
(bony growth) on its underside. The growth probably resulted from the conversion of cartilage
or a ligament
to bone during development, but the cause of the ossification was not determined. Hypervitaminosis A
and bone spur
s were ruled out, and an osteoma
(benign bone tumor) was deemed unlikely. Another specimen, a small caudal (tail) vertebra, was also found to have an abnormal growth, this time on the top of its neural spine
, which projects upwards from the vertebrae, allowing muscle attachment. Similar growths from the neural spine have been found in specimens of Allosaurus
and Masiakasaurus, probably resulting from the ossification of a ligament running either between the neural spines (interspinal ligament
) or along their tops (supraspinal ligament).
The most serious pathology discovered was in a series of five large tail vertebrae. The first two vertebrae showed only minor abnormalities with the exception of a large groove that extended along the left side of both bones. However, the next three vertebrae were completely fused together at many different points, forming a solid bony mass. There is no sign of any other vertebrae after the fifth in the series, indicating that the tail ended there prematurely. From the size of the last vertebrae, scientists judged that about ten vertebrae were lost. 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. Alternatively, the infection may have come first and led to the end of the tail becoming necrotic
and falling off. This is the first example of tail truncation known in a non-avian theropod dinosaur.
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 65.5 Ma (million years ago). Majungasaurus teeth are found up until the very end of the Maastrichtian, when all non-avian dinosaurs went 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 10–15°
more southerly in latitude
than it is today. The prevailing climate
of the time was semi-arid, with pronounced season
ality 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 flow
s through 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 marine
environment.
Besides Majungasaurus, fossil taxa recovered from the Maevarano include fish
, frog
s, 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of abelisaurid theropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
that lived in Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
from 70 to 65.5 million years ago, at the end of the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period. Only one species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
(M. 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 biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...
al 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
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
, 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
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
. It appears to be most closely related to abelisaurids from India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
rather than South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
or continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
al Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, a fact which has important biogeographical
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
implications. Majungasaurus was the apex predator
Apex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
in its ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
, mainly preying on sauropods like Rapetosaurus
Rapetosaurus
Rapetosaurus is a genus of sauropod dinosaur that lived in Madagascar from 70 to 65 million years ago, at the end of the Cretaceous Period. Only one species Rapetosaurus is a genus of sauropod dinosaur that lived in Madagascar from 70 to 65 million years ago, at the end of the Cretaceous Period....
, and is also one of the few dinosaurs for which there is direct evidence of cannibalism
Cannibalism (zoology)
In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...
.
Description
Majungasaurus was a medium-sized theropod that typically measured 6–7 meters (20–23 ft) in length, including its tail. Fragmentary remains of larger individuals indicate that some adults reached lengths of more than 8 meters (26 ft). Scientists estimate that an average adult Majungasaurus weighed more than 1100 kilogramKilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
s (2400 lb
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
), although the largest animals would have weighed more. Its 8–9 meter (26–30 ft) relative Carnotaurus
Carnotaurus
Carnotaurus was a large predatory dinosaur. Only one species, Carnotaurus sastrei has been described so far.Carnotaurus lived in Patagonia, Argentina during the Campanian or Maastrichtian stage of the Late Cretaceous...
has been estimated to weigh 1500 kilograms (3300 lb).
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
(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 bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s 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 bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
s on top of the skull as well. In life, these structures would have been covered with some sort of integument, possibly made of keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
. Computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
(CT scanning) of the skull shows that both the nasal structure and the frontal horn contained hollow sinus
Sinus (anatomy)
Sinus is Latin for "bay", "pocket", "curve", or "bosom". In anatomy, the term is used in various contexts.A sinus is a sack or cavity in any organ or tissue, or an abnormal cavity or passage caused by the destruction of tissue...
cavities, perhaps to reduce weight. The teeth were typical of abelisaurids in having short crowns
Crown (tooth)
In dentistry, crown refers to the anatomical area of teeth, usually covered by enamel. The crown is usually visible in the mouth after developing below the gingiva and then erupting into place.-References:...
, although Majungasaurus bore 17 teeth in both the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
of the upper jaw and the dentary of the lower jaw, more than in any other abelisaurid except Rugops
Rugops
Rugops is a genus of theropod dinosaur which inhabited what is now Africa approximately 95 million years ago...
.
The postcrania
Postcrania
Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...
l skeleton of Majungasaurus closely resembles those of Carnotaurus and Aucasaurus
Aucasaurus
Aucasaurus was a genus of medium-sized theropod dinosaur from Argentina that lived during the Santonian stage . It was smaller than the related Carnotaurus, although more derived in some ways, such as its extremely reduced arms and almost total lack of fingers.The type skeleton is complete to the...
, 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
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
over the hips. Although the cervical (neck
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
) vertebrae had numerous cavities and excavations (pleurocoels) to reduce their weight, they were robust, with exaggerated muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
attachment sites and rib
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
s that interlocked for strength. Ossified
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
s 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
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
(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. 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.
Like other abelisaurids, the hindlimbs were stocky and short compared to body length. The tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
(lower leg bone) of Majungasaurus was even stockier than that of its relative Carnotaurus, with a prominent crest on the knee. The astragalus
Talus bone
-External links:* *...
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.
Classification and systematics
Majungasaurus is classified as a member of the theropod cladeClade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Abelisauridae, which is considered a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
in Linnaean taxonomy
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
. Along with the family Noasauridae
Noasauridae
Noasaurids were a group of theropod dinosaurs from the Cretaceous Period . They were generally small in size...
, abelisaurids are included in the superfamily Abelisauroidea, which is in turn a subdivision of the infraorder Ceratosauria
Ceratosauria
Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is presently no universally agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived...
. Abelisaurids are known for their tall skulls with blunt snouts, extensive sculpturing on the outer surfaces of the facial bones (convergent
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
with carcharodontosaurids), very reduced (atrophied
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
) forelimbs (convergent with tyrannosaurids), and stocky hindlimb proportions, among other features.
As with many dinosaur families, the systematics
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
(evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary relationships) within the family Abelisauridae are confused. Several cladistic studies have indicated that Majungasaurus shares a close relationship with Carnotaurus from South America, while others were unable to firmly place it in the phylogeny. The most recent analysis, using the most complete information, instead recovered Majungasaurus in a clade with Rajasaurus
Rajasaurus
Rajasaurus is a genus of carnivorous abelisaurian theropod dinosaur with an unusual head crest. Between 1982 and 1984, its fossilized bones were discovered by Suresh Srivastava of the Geological Survey of India...
and Indosaurus
Indosaurus
Indosaurus is a genus of theropod dinosaur once living in what is now India. It lived approximately 69 million years ago, in the Maastrichtian division of the Late Cretaceous...
from India, but excluding South American genera like Carnotaurus, Ilokelesia
Ilokelesia
Ilokelesia is a primitive abelisaur found in 1991, preserved in the layers of the earliest Late Cretaceous of the Río Limay Formation, Neuquén Group, located near Plaza Huincul, Neuquén Province, Argentina. The specimen, consisting of very fragmentary elements of the skull, the axial and the...
, Ekrixinatosaurus
Ekrixinatosaurus
Ekrixinatosaurus is a genus of dinosaur which lived during the Late Cretaceous. It was a theropod believed to be one of the abelisaurs. Its fossils have been found in Argentina...
, Aucasaurus and Abelisaurus
Abelisaurus
Abelisaurus is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Period of what is now South America. It was a bipedal carnivore that probably reached 7 to 9 meters in length, although it is known from only one partial skull.The generic name recognizes Roberto Abel as the...
, as well as Rugops from mainland Africa. This leaves open the possibility of separate clades of abelisaurids in western and eastern Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
. Detailed description of known abelisaurids like Aucasaurus as well as future discoveries and analyses may help to resolve the phylogenetic picture.
Discovery and naming
FrenchFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
paleontologist Charles Depéret
Charles Depéret
Charles Jean Julien Depéret was a French geologist and paleontologist. He was a member of the French Academy of Sciences, the Société géologique de France and dean of the Science faculty of Lyon....
described the first theropod remains from northwestern Madagascar in 1896. These included two teeth, a claw, and some vertebrae discovered along the Betsiboka River
Betsiboka River
Betsiboka River is a long river in central-north Madagascar. It flows northwestward and empties to Bombetoka Bay, forming a large delta. The river is distinct for its red-coloured water, which is caused by river sediments. The river carries an enormous amount of reddish-orange silt to the sea...
by a French army officer and deposited in the collection of what is now the Université Claude Bernard Lyon 1
Université Claude Bernard Lyon 1
The Université Claude Bernard Lyon 1, also known as Université Lyon 1 or UCBL, is one of the three public universities of Lyon, France. The dominant areas of study covered by the university are science and medicine. The main administrative, teaching and research facilities are located in...
. Depéret referred these fossils to the genus Megalosaurus
Megalosaurus
Megalosaurus is a genus of large meat-eating theropod dinosaurs of the Middle Jurassic period of Europe...
, which at the time was a wastebasket taxon containing any number of unrelated large theropods, as the new species M. crenatissimus. This name is derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
word crenatus ("notched") and the suffix
Suffix
In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns or adjectives, and verb endings, which form the conjugation of verbs...
-issimus ("most"), in reference to the numerous serrations on both front and rear edges of the teeth. Depéret later reassigned the species to the North American genus Dryptosaurus
Dryptosaurus
Dryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
, another poorly known taxon.
Numerous fragmentary remains from Mahajanga Province
Mahajanga Province
Mahajanga is a former province of Madagascar with an area of 150,023 km². It had a population of 1,896,000 . Its capital was Mahajanga.Except for Fianarantsoa, Mahajanga Province bordered all of the country's other provinces:...
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
Muséum national d'histoire naturelle
The Muséum national d'Histoire naturelle is the National Museum of Natural History in Paris, France.- History :The museum was formally founded on 10 June 1793, during the French Revolution...
in Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
. In 1955, René Lavocat
René Lavocat
René Lavocat is a French paleontologist who described several genera of African dinosaurs including the sauropod Rebbachisaurus.-References:...
described a theropod dentary with teeth from the Maevarano Formation
Maevarano Formation
The Maevarano Formation is an Upper Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age, and records a seasonal, semiarid environment with rivers that had greatly varying discharges...
in the same region where the original material was found. The teeth matched those first described by Depéret, but the strongly curved jaw bone was very different from both Megalosaurus and Dryptosaurus. Lavocat renamed the genus Majungasaurus, using an older spelling of Mahajanga as well as the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word σαυρος/sauros (meaning "lizard"), and made this jaw bone (MNHN
Muséum national d'histoire naturelle
The Muséum national d'Histoire naturelle is the National Museum of Natural History in Paris, France.- History :The museum was formally founded on 10 June 1793, during the French Revolution...
.MAJ 1) the type specimen. Hans-Dieter Sues
Hans-Dieter Sues
Hans-Dieter Sues is a German-born paleontologist who is Senior Scientist and Curator of Vertebrate Paleontology at the National Museum of Natural History of the Smithsonian Institution in Washington, DC. He received his education at Johannes Gutenberg-Universität Mainz , University of Alberta, and...
and Philippe Taquet
Philippe Taquet
Philippe Taquet is a French paleontologist who specializes in dinosaur systematics of finds primarily in northern Africa.He is a member of the French Academy of Sciences since November 30, 2004...
described a dome-shaped skull fragment (MNHN.MAJ 4) as a new genus of pachycephalosaur (Majungatholus atopus) in 1979. This was the first report of a pachycephalosaur in the Southern Hemisphere.
In 1993, scientists from the State University of New York at Stony Brook
State University of New York at Stony Brook
The State University of New York at Stony Brook, also known as Stony Brook University, is a public research university located in Stony Brook, New York, on the North Shore of Long Island, about east of Manhattan....
and the University of Antananarivo
University of Antananarivo
University of Antananarivo is the primary public university of Madagascar, located in the capital Antananarivo.The school traces its founding to 16 December 1955 and the formation of the Institute for Advanced Studies in Antananarivo. It quickly established itself as the main center for higher...
began the Mahajanga Basin Project, a series of expeditions to examine the fossils and geology of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
sediments near the village of Berivotra, in Mahajanga Province. Among these scientists was paleontologist David W. Krause
David W. Krause
David W. Krause is a Canadian-born vertebrate paleontologist currently working as a Distinguished Service Professor at the Stony Brook University Department of Anatomical Sciences. His work primarily focuses on fossils from the Cretaceous period of Madagascar, and he often travels to the island to...
of Stony Brook. The first expedition turned up hundreds of theropod teeth identical to those of Majungasaurus, some of which were attached to an isolated premaxilla that was described in 1996. The following seven expeditions would turn up tens of thousands of fossils, many of which belonged to species new to science. The Mahajanga Basin Project claims credit for quintupling the known diversity of fossil taxa in the region.
Fieldwork in 1996 turned up a spectacularly complete theropod skull preserved in exquisite detail (FMNH
Field Museum of Natural History
The Field Museum of Natural History is located in Chicago, Illinois, USA. It sits on Lake Shore Drive next to Lake Michigan, part of a scenic complex known as the Museum Campus Chicago...
PR 2100). On top of this skull was a dome-shaped swelling nearly identical to the one described by Sues and Taquet as Majungatholus atopus. Majungatholus was redescribed as an abelisaurid rather than a pachycephalosaur in 1998. Although the name Majungasaurus crenatissimus was older than Majungatholus atopus, the authors judged the type dentary of Majungasaurus too fragmentary to confidently assign to the same species as the skull. 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. Project members also collected hundreds of isolated bones and thousands of shed Majungasaurus teeth. Taken together, these remains represent nearly all the bones of the skeleton, although most of the forelimbs, most of the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
and the tip of the tail are still unknown. This fieldwork culminated in a 2007 monograph
Monograph
A monograph is a work of writing upon a single subject, usually by a single author.It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself...
consisting of seven scientific papers on all aspects of the animal's biology, published in the Society of Vertebrate Paleontology
Society of Vertebrate Paleontology
The Society of Vertebrate Paleontology was founded in 1940 for individuals with an interest in vertebrate paleontology. SVP now has almost 2,000 members. The society's website states that SVP "is organized exclusively for educational and scientific purposes...
Memoirs. The papers are in English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
, although each has an abstract
Abstract (summary)
An abstract is a brief summary of a research article, thesis, review, conference proceeding or any in-depth analysis of a particular subject or discipline, and is often used to help the reader quickly ascertain the paper's purpose. When used, an abstract always appears at the beginning of a...
written in Malagasy
Malagasy language
Malagasy is the national language of Madagascar, a member of the Austronesian family of languages. Most people in Madagascar speak it as a first language as do some people of Malagasy descent elsewhere.-History:...
. In this volume, the dentary described by Lavocat was re-evaluated and determined to be diagnostic for this species. Therefore, the name Majungatholus was replaced by the older name Majungasaurus. Although the monograph is comprehensive, the editors noted that it describes only material recovered from 1993 through 2001. A significant quantity of specimens, some very complete, were excavated in 2003 and 2005 and await preparation and description in future publications.
Skull ornamentation
Majungasaurus is perhaps most distinctive for its skull ornamentation, including the swollen and fused nasals and the frontal horn. Other ceratosaurs, including Carnotaurus, Rajasaurus, and CeratosaurusCeratosaurus
Ceratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
itself bore crests on the head. These structures are likely to have played a role in intraspecific competition
Intraspecific competition
Intraspecific competition is a particular form of competition in which members of the same species vie for the same resource in an ecosystem...
, although their exact function within that context is unknown. The hollow cavity inside the frontal horn of Majungasaurus would have weakened the structure and probably precluded its use in direct physical combat, although the horn may have served a display
Display (zoology)
Display is a form of animal behaviour, linked to survival of the species in various ways. One example of display used by some species can be found in the form of courtship, with the male usually having a striking feature that is distinguished by colour, shape or size, used to attract a female...
purpose. While there is variation in the ornamentation of Majungasaurus individuals, there is no evidence for sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
.
Feeding
Scientists have suggested that the unique skull shape of Majungasaurus and other abelisaurids indicate different predatory habits than other theropods. Whereas most theropods were characterized by long, low skulls of narrow width, abelisaurid skulls were taller and wider, and often shorter in length as well. The narrow skulls of other theropods were well-equipped to withstand the vertical stress of a powerful bite, but not as good at withstanding torsionTorsion (mechanics)
In solid mechanics, torsion is the twisting of an object due to an applied torque. In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius....
(twisting). In comparison to modern mammalian predators
Carnivora
The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...
, 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.
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. Majungasaurus had an even broader snout than other abelisaurids, and other aspects of its anatomy may also support the bite-and-hold hypothesis. The neck was strengthened, with robust vertebrae, interlocking ribs and ossified tendons, as well as reinforced muscle attachment sites on the vertebrae and the back of the skull. These muscles would have been able to hold the head steady despite the struggles of its prey. Abelisaurid skulls were also strengthened in many areas by bone mineralized
Mineralization (biology)
In biology, mineralization refers to the process where an organic substance is converted to an inorganic substance.This may also be a normal biological process which takes place during the life of an organism such as the formation of bone tissue or egg shells, largely with calcium.This term may...
out of the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, creating the characteristic rough texture of the bones. This is particularly true of Majungasaurus, where the nasal bones were fused and thickened for strength. On the other hand, the lower jaw of Majungasaurus sported a large fenestra (opening) on each side, as seen in other ceratosaurs, as well as synovial joint
Synovial joint
A Synovial joint, also known as a diarthrosis, is the most common and most movable type of joint in the body of a mammal. As with most other joints, synovial joints achieve movement at the point of contact of the articulating bones....
s between certain bones that allowed a high degree of flexibility in the lower jaw, although not to the extent seen in snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s. This may have been an adaptation to prevent the fracture of the lower jaw when holding onto a struggling prey animal. The front teeth of the upper jaw were more robust than the rest, to provide an anchor point for the bite, while the low crown height of Majungasaurus teeth prevented them from breaking off during a struggle. Finally, unlike the teeth of Allosaurus
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...
and most other theropods, which were curved on both the front and back, abelisaurids like Majungasaurus had teeth curved on the front edge but straighter on the back (cutting) edge. This structure may have served to prevent slicing, and instead holding the teeth in place when biting.
Cannibalism
Although sauropods may have been the prey of choice for Majungasaurus, recent discoveries in Madagascar indicate another surprising component of its diet: other Majungasaurus. Numerous bones of Majungasaurus have been discovered bearing tooth marks identical to those found on sauropod bones from the same localities. These marks have the same spacing as teeth in Majungasaurus jaws, are of the same size as Majungasaurus teeth, and contain smaller notches consistent with the serrations on those teeth. As Majungasaurus is the only large theropod known from the area, the simplest explanation is that it was feeding on other members of its own species. Suggestions that the TriassicTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
Coelophysis
Coelophysis
Coelophysis , meaning "hollow form" in reference to its hollow bones , is one of the earliest known genera of dinosaur...
was a cannibal have been recently disproven, leaving Majungasaurus as the only non-avian theropod with confirmed cannibalistic tendencies, although there is some evidence that cannibalism may have occurred in other species as well.
It is unknown if Majungasaurus actively hunted their own kind or only scavenged
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
their carcasses. However, some researchers have noted that modern Komodo monitors sometimes kill each other when competing for access to carcasses. The lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s will then proceed to cannibalize the remains of their rivals, which may suggest similar behavior in Majungasaurus and other theropods.
Respiratory system
Scientists have reconstructed the respiratory systemRespiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
of Majungasaurus based on a superbly preserved series of vertebrae (UA
University of Antananarivo
University of Antananarivo is the primary public university of Madagascar, located in the capital Antananarivo.The school traces its founding to 16 December 1955 and the formation of the Institute for Advanced Studies in Antananarivo. It quickly established itself as the main center for higher...
8678) recovered from the Maevarano Formation. Most of these vertebrae and some of the ribs contained cavities (pneumatic foramina) that may have resulted from the infiltration of avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
-style lungs and air sacs. In birds, the neck vertebrae and ribs are hollowed out by the cervical air sac, the upper back vertebrae by the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
, and the lower back and sacral
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
(hip) vertebrae by the abdominal air sac. Similar features in Majungasaurus vertebrae imply the presence of these air sacs. These air sacs may have allowed for a basic form of avian-style 'flow-through ventilation,' where air flow through the lungs is one-way, so that oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
-rich air inhaled from outside the body is never mixed with exhaled air laden with carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. This method of respiration, while complicated, is highly efficient.
The recognition of pneumatic foramina in Majungasaurus, besides providing an understanding of its respiratory biology, also has larger-scale implications for evolutionary biology. The split between the ceratosaur line, which led to Majungasaurus, and the tetanuran
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
line, to which birds belong, occurred very early in the history of theropods. The avian respiratory system, present in both lines, must therefore have evolved before the split, and well before the evolution of birds themselves. This provides further evidence of the dinosaurian origin of birds.
Brain and inner ear structure
Computed tomographyComputed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
, also known as CT scanning, of a complete Majungasaurus skull (FMNH PR 2100) allowed a rough reconstruction of its brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
and inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
structure. Overall, the brain was very small relative to body size, but otherwise similar to many other non-coelurosauria
Coelurosauria
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
n theropods, with a very conservative form closer to modern crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns than to birds. One difference between Majungasaurus and other theropods was its smaller flocculus, a region of the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
that helps to coordinate movements of the eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
with movements of the head. This suggests that Majungasaurus and other abelisaurids like Indosaurus
Indosaurus
Indosaurus is a genus of theropod dinosaur once living in what is now India. It lived approximately 69 million years ago, in the Maastrichtian division of the Late Cretaceous...
, which also had a small flocculus, did not rely on quick head movements to sight and capture prey.
Inferences about behavior can also be drawn from examination of the inner ear. The semicircular canals within the inner ear aid in balance, and the lateral semicircular canal is usually parallel to the ground when the animal holds its head in an alert posture. When the skull of Majungasaurus is rotated so that its lateral canal is parallel to the ground, the entire skull is nearly horizontal. This contrasts with many other theropods, where the head was more strongly downturned when in the alert position. The lateral canal is also significantly longer in Majungasaurus than in its more basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
relative Ceratosaurus
Ceratosaurus
Ceratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
, indicating a greater sensitivity to side-to-side motions of the head.
Pathology
A 2007 report described pathologiesPathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
in the bones of Majungasaurus. Scientists examined the remains of at least 21 individuals and discovered four with noticeable pathologies. While pathology had been studied in large tetanuran
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
theropods like allosaurid
Allosaurid
Allosauridae was a family of medium to large sized carnivorous theropod dinosaurs. Members included Saurophaganax, Allosaurus, and the poorly known Epanterias, which could well be a specimen of Allosaurus...
s and tyrannosaurids, this was the first time an abelisauroid had been examined in this manner. No wounds were found on any skull elements, in contrast to tyrannosaurids where sometimes gruesome facial bites were common. One of the specimens was a phalanx
Phalanx bones
In anatomy, phalanx bones are those that form the fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three. Phalanges are classified as long bones.The phalanges do not have individual names...
(toe bone) of the foot, which had apparently been broken and subsequently healed.
Most of the pathologies occurred on the vertebrae. For example, a dorsal (back) vertebra from a juvenile animal showed an exostosis
Exostosis
An exostosis is the formation of new bone on the surface of a bone. Exostoses can cause chronic pain ranging from mild to debilitatingly severe, depending on where they are located and what shape they are....
(bony growth) on its underside. The growth probably resulted from the conversion of cartilage
Endochondral ossification
Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...
or a ligament
Ligament
In anatomy, the term ligament is used to denote any of three types of structures. Most commonly, it refers to fibrous tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.Ligament can also refer to:* Peritoneal...
to bone during development, but the cause of the ossification was not determined. Hypervitaminosis A
Hypervitaminosis A
Hypervitaminosis A refers to the effects of excessive vitamin A intake.-Presentation:Effects include* Birth defects* Liver problems* Reduced bone mineral density that may result in osteoporosis* Coarse bone growths...
and bone spur
Bone spur
Osteophytes, commonly referred to as bone spurs, are bony projections that form along joint margins. They should not be confused with enthesophytes, which are bony projections which form at the attachment of a tendon or ligament.-Pathophysiology:...
s were ruled out, and an osteoma
Osteoma
An osteoma is a new piece of bone usually growing on another piece of bone, typically the skull. It is a benign tumor.When the bone tumor grows on other bone it is known as "homoplastic osteoma"; when it grows on other tissue it is called "heteroplastic osteoma".Osteoma represents the most common...
(benign bone tumor) was deemed unlikely. Another specimen, a small caudal (tail) vertebra, was also found to have an abnormal growth, this time on the top of its neural spine
Spinous process
The spinous process of a vertebra is directed backward and downward from the junction of the laminae , and serves for the attachment of muscles and ligaments. In animals without an erect stance, the process points upward and may slant forward or backward...
, which projects upwards from the vertebrae, allowing muscle attachment. Similar growths from the neural spine have been found in specimens of Allosaurus
Specimens of Allosaurus
Allosaurus was not only one of the most abundant Late Jurassic dinosaurs, but also one of the best known. Its brain, anatomy and even behaviour were studied more accurate than those of any dinosaur on Earth. Many of its specimens were found: from Utah, Wyoming, Colorado and Montana to Portugal...
and Masiakasaurus, probably resulting from the ossification of a ligament running either between the neural spines (interspinal ligament
Interspinal ligament
The interspinal ligaments , thin and membranous, connect adjoining spinous processes and extend from the root to the apex of each process.They meet the ligamenta flava in front and the supraspinal ligament behind....
) or along their tops (supraspinal ligament).
The most serious pathology discovered was in a series of five large tail vertebrae. The first two vertebrae showed only minor abnormalities with the exception of a large groove that extended along the left side of both bones. However, the next three vertebrae were completely fused together at many different points, forming a solid bony mass. There is no sign of any other vertebrae after the fifth in the series, indicating that the tail ended there prematurely. From the size of the last vertebrae, scientists judged that about ten vertebrae were lost. One explanation for this pathology is severe physical trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
resulting in the loss of the tail tip, followed by osteomyelitis
Osteomyelitis
Osteomyelitis simply means an infection of the bone or bone marrow...
(infection) of the last remaining vertebrae. Alternatively, the infection may have come first and led to the end of the tail becoming necrotic
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
and falling off. This is the first example of tail truncation known in a non-avian theropod dinosaur.
Paleoecology
Mahajanga Province
Mahajanga is a former province of Madagascar with an area of 150,023 km². It had a population of 1,896,000 . Its capital was Mahajanga.Except for Fianarantsoa, Mahajanga Province bordered all of the country's other provinces:...
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
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
, evidence from biostratigraphy
Biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period...
and paleomagnetism
Paleomagnetism
Paleomagnetism is the study of the record of the Earth's magnetic field in rocks. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of...
suggest that they were deposited during the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
, which lasted from 70 to 65.5 Ma (million years ago). Majungasaurus teeth are found up until the very end of the Maastrichtian, when all non-avian dinosaurs went extinct.
Then as now, Madagascar was an island, having separated
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
from the Indian subcontinent
Indian subcontinent
The Indian subcontinent, also Indian Subcontinent, Indo-Pak Subcontinent or South Asian Subcontinent is a region of the Asian continent on the Indian tectonic plate from the Hindu Kush or Hindu Koh, Himalayas and including the Kuen Lun and Karakoram ranges, forming a land mass which extends...
less than 20 million years earlier. It was drifting northwards but still 10–15°
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
more southerly in latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
than it is today. The prevailing climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
of the time was semi-arid, with pronounced season
Season
A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...
ality in temperature and rainfall. Majungasaurus inhabited a coastal flood plain cut by many sandy river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
channels
Channel (geography)
In physical geography, a channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks.A channel is also the natural or human-made deeper course through a reef, sand bar, bay, or any shallow body of water...
. Strong geological evidence suggests the occurrence of periodic debris flow
Debris flow
A debris flow is a fast moving, liquefied landslide of unconsolidated, saturated debris that looks like flowing concrete. It is differentiated from a mudflow in terms of the viscosity and textural properties of the flow. Flows can carry material ranging in size from clay to boulders, and may...
s through 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
Berivotra Formation
The Berivotra Formation is an Upper Cretaceous sedimentary rock marine formation found in Madagascar, that is contemporary to the terrestrial Maevarano Formation....
represents the contemporaneous marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
environment.
Besides Majungasaurus, fossil taxa recovered from the Maevarano include fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s, lizards, snakes, seven distinct species of crocodylomorphs, five or six species of mammals, Vorona
Vorona
Vorona is a monotypic genus of prehistoric birds. It was described from fossils found in a Maevarano Formation quarry near the village of Berivotra, Mahajanga Province, Madagascar. The age is Late Cretaceous, probably Campanian . V...
and several other birds, the possibly flighted dromaeosaurid Rahonavis
Rahonavis
Rahonavis is a genus of bird-like dinosaur from the Late Cretaceous of what is now northwestern Madagascar. It is known from a partial skeleton found in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province...
, the noasaurid Masiakasaurus
Masiakasaurus
Masiakasaurus was a small predatory theropod dinosaur from the Late Cretaceous of Madagascar. It was named in 2001 by Scott D. Sampson, Matthew Carrano, and Catherine A. Forster. Unlike most theropods, the front teeth of Masiakasaurus projected forward instead of straight down...
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
Mahajangasuchus
Mahajangasuchus is an extinct genus of crocodyliform which had blunt, conical teeth. The type species, M. insignis, lived during the Late Cretaceous; its fossils have been found in the Maevarano Formation in northern Madagascar.Sereno et al....
and Trematochampsa
Trematochampsa
Trematochampsa is an extinct genus of crocodyliform from the Late Cretaceous In Beceten Formation of Niger. The type species, T. taqueti, was described by Eric Buffetaut in 1974. A second species, T. oblita, was named from Madagascar in 1979...
might have competed with it closer to water.
External links
- Majungasaurus entry in The Theropod Database.
- Press release about the Majungasaurus mount erected in 2006 at SUNY - Stony Brook.