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| color = pink
| color = pink
| name = ''Majungasaurus''
| name = ''Majungasaurus''
| status = fossil
| fossil_range = [[Late Cretaceous]]
| fossil_range = [[Late Cretaceous]]
| image = Majungatholus -1.jpg
| image = Majungatholus -1.jpg
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| familia = [[Abelisaur]]idae
| familia = [[Abelisaur]]idae
| genus = '''''Majungasaurus'''''
| genus = '''''Majungasaurus'''''
| subdivision_ranks = [[Species]]
| binomial = ''Majungasaurus crenatissimus''
| binomial_authority = Lavocat, 1955
| subdivision = *'''''M. crenatissimus'''''<br/><small>Lavocat, 1955</small>
| synonyms =
| synonyms =
''Majungatholus atopus'' <small>Sues and Taquet, 1979</small><br>
''Megalosaurus crenatissimus''<br/><small>Depéret, 1896</small><br/>
''Dryptosaurus crenatissimus''<br/><small>Depéret & Savornin, 1928</small><br/>
''Majungatholus atopus''<br/> <small>Sues and Taquet, 1979</small>
}}
}}


'''''Majungasaurus''''' (meaning "Majunga lizard") was an [[abelisaur]] of the infraorder [[Ceratosauria]]. Named for the [[Mahajunga]] district in [[Madagascar]] in which it was found, the ''Majungasaurus'' is known from a partial lower jaw uncovered from the [[Maevarano Formation]]. It appears to be similar to ''[[Abelisaurus]]'' and ''[[Carnotaurus]]''.
'''''Majungasaurus''''' ([[IPA chart for English|pronounced]] {{IPA|/məˌdʒungə'sɔɹəs/}} or mah-JOON-gah-''SAWR''-us; meaning 'Mahajanga lizard') is a [[genus]] of [[abelisaurid]] [[theropod]] [[dinosaur]] that lived in what is now [[Madagascar]] from 70 to 65 [[million years ago]], at the end of the [[Cretaceous]] [[Period (geology)|Period]]. Only one [[species]] (''M. crenatissimus'') has been identified. This dinosaur was briefly referred to the genus ''Majungatholus'', which is now considered a [[junior synonym]].


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.
More well-preserved specimens discovered between [[1993]] and [[1996]] were originally considered examples of ''Majungasaurus'' as well, but researchers later placed them in another genus, named ''[[Majungatholus]]''. One particularly good ''Majungatholus'' specimen had an unusually thick skull; thus, when its skull cap was first discovered in [[Madagascar]], scientists thought that it was the skull of a [[pachycephalosaur]]. (Hence its name, which meant "Majunga dome"). Several years later, when a full skull and more complete skeleton were found, scientists realized it was an abelisaurid theropod, and probably even synonymous with the previously known dinosaur ''Majungasaurus''. The supposed dome, for example, now appears to be the round and hollow horn of the [[theropod]].


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 [[biogeography|biogeographical]] implications. ''Majungasaurus'' was the [[apex predator]] in its [[ecosystem]], preying on [[sauropod]]s like ''[[Rapetosaurus]]'', but is also the only dinosaur for which direct evidence of [[Cannibalism (zoology)|cannibalism]] is known.
The ''Majungasaurus'' is believed by some scientists to have been [[cannibal]]istic, due to fossil specimens featuring tooth marks that appear to have been inflicted by members of their own species.


===References===
==Description==
''Majungasaurus'' was a medium-sized theropod that typically measured 6–7&nbsp;[[meter]]s (20–23&nbsp;[[foot (unit of length)|ft]]) in length, including its tail.<ref name=krauseetal2007>{{cite_book |last=Krause |first=David W. |coauthors=Sampson, Scott D.; Carrano, Matthew T.; & O'Connor, Patrick M. |year=2007 |chapter=Overview of the history of discovery, taxonomy, phylogeny, and biogeography of ''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |editor=Sampson, Scott D.; & Krause, David W. (eds.) |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=1-20 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282007%2927%5B1%3AOOTHOD%5D2.0.CO%3B2}}</ref> Fragmentary remains of larger individuals indicate that some adults reached lengths of more than 8&nbsp;meters (26&nbsp;ft).<ref name=sampsonwitmer2007>{{cite_book |last=Sampson |first=Scott D. |coauthors=& Witmer, Lawrence M. |year=2007 |chapter=Cranofacial anatomy of ''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar|editor=Sampson, Scott D.; & Krause, David W. (eds.) |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=32-102 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282007%2927%5B32%3ACAOMCT%5D2.0.CO%3B2}}</ref> There has been no published estimation of its mass, although its 8–9&nbsp;meter (26–30&nbsp;ft) relative ''[[Carnotaurus]]'' has been estimated to weigh 1500&nbsp;[[kilogram]]s (3300&nbsp;[[Pound (mass)|lb]]).<ref name=mazettaetal1998>{{cite_journal |last=Mazzetta |first=Gerardo V. |coauthors=Fariña, Richard A.; & Vizcaíno, Sergio F. |year=1998 |title=On the paleobiology of the South American horned theropod ''Carnotaurus sastrei'' Bonaparte |journal=Gaia |volume=15 |pages=185-192 |url=http://www.mnhn.ul.pt/geologia/publicageo.htm}}</ref>
* Lavocat, R. (1955). "Sur une portion de mandibule de Théropode provenant du Crétacé supérieur de Madagascar." ''Bull. Mus. Hist. Nat. Paris'', '''27''': 256-259.

* Sampson, S.D., Krause, D.W, Dodson, P. and Forster, C.A. (1996). "The premaxilla of ''Majungasaurus'' (Dinosauria; Theropoda), with implications for Gondwanan palaeobiogeography." ''Journal of Vertebrate Paleontology'', '''16''': 601-605.
The skull of ''Majungasaurus'' is exceptionally well-known compared to most other theropods and generally similar to that of other abelisaurids. Like most 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&nbsp;[[centimeter]]s (24–28&nbsp;[[inch|in]]) long. The tall [[premaxilla]] (upper jaw bone), making 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 (anatomy)|sinus]] cavities, perhaps to reduce weight.<ref name=sampsonwitmer2007/> The teeth were typical of abelisaurids in having short [[Crown (tooth)|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]]''.<ref name=smith2007>{{cite_book |last=Smith |first=Joshua B. |year=2007 |chapter=Dental morphology and variation in ''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |editor=Sampson, Scott D.; & Krause, David W. (eds.) |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=103-126 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282007%2927%5B103%3ADMAVIM%5D2.0.CO%3B2}}</ref>
* Sampson, S., Witmer, L., Forster, C., Krause, D., O’Connor, P., Dodson, P. and Ravoavy, F. (1998). "Predatory dinosaur remains from Madagascar: Implications for the Cretaceous Biogeography of Gondwana." ''Science'', '''280''': 1048-1051.

* Sues, H., and Taquet, P. (1979). "A pachycephalosaurid dinosaur from Madagascar and a Laurasia-Gondwanaland connection in the Cretaceous." ''Nature''m '''279'''(5714): 633-635.
The [[postcrania]]l skeleton of ''Majungasaurus'' closely resembles that 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]]) [[vertebra]]e 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. [[Ossification|Ossified]] [[tendon]]s attached to the cervical ribs gave 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.<ref name=oconnor2007>{{cite_book |last=O'Connor |first=Patrick M. |year=2007 |chapter=The postcranial axial skeleton of ''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |editor=Sampson, Scott D.; & Krause, David W. (eds.) |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=127-162 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282007%2927%5B127%3ATPASOM%5D2.0.CO%3B2}}</ref> The [[humerus]] (upper arm bone) is the only preserved bone of the forelimb, but it was short and curved, closely resembling those of ''Aucasaurus'' and ''Carnotaurus''. This may indicate that ''Majungasaurus'' had similar very short forelimbs with four digits. The hindlimbs of all abelisaurids were stocky and short compared to body length, but the [[tibia]] (lower leg bone) of ''Majungasaurus'' was even stockier than that of its relative ''Carnotaurus''. 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.<ref name=carrano2007>{{cite_book |last=Carrano |first=Matthew T. |year=2007 |chapter=The appendicular skeleton of ''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |editor=Sampson, Scott D.; & Krause, David W. (eds.) |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=163-179 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282007%2927%5B163%3ATASOMC%5D2.0.CO%3B2}}</ref>

==Classification and systematics==
''Majungasaurus'' is classified as a member of the theropod [[clade]] Abelisauridae, which is considered a family in [[Linnaean taxonomy]]. Along with the family [[Noasauridae]], abelisaurids are included in the superfamily [[Abelisauroidea]], which is in turn a subdivision of the [[infraorder]] [[Ceratosauria]].<ref name=krauseetal2007/><ref name=serenoetal2004>{{cite_journal |last=Sereno |first=Paul C. |authorlink=Paul Sereno |year=2007 |title=New dinosaurs link southern landmasses in the Mid-Cretaceous |journal=Proceedings of the Royal Society of London B: Biological Sciences |volume=271 |issue=1546 |pages=1325-1330 |doi=10.1098/rspb.2004.2692}}</ref> Abelisaurids are known for their tall skulls with blunt snouts, extensive sculpturing on the outer surfaces of the facial bones ([[convergent evolution|convergent]] with [[carcharodontosaurid]]s), [[atrophy|atrophied]] forelimbs (convergent with [[tyrannosaurid]]s), and stocky hindlimb proportions, among other features.<ref name=tykoskirowe2004>{{cite_book |last=Tykoski |first=Ronald B. |coauthors=& Rowe, Timothy. |year=2004 |chapter=Ceratosauria |editor=[[David Weishampel|Weishampel, David B.]]; [[Peter Dodson|Dodson, Peter]]; & & Osmólska, Halska (eds.) |title=The Dinosauria |edition=Second Edition |publisher=University of California Press |location=Berkeley |pages=47-70 |isbn=0-520-24209-2}}</ref>

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,<ref name=serenoetal2004/><ref name=tykoskirowe2004/> while others were unable to firmly place it in the [[phylogeny]].<ref name=coriaetal2002>{{cite_journal |last=Coria |first=Rodolfo A. |authorlink=Rodolfo Coria |coauthors=Chiappe, Luis M.; & Dingus, Lowell. |year=2002 |title=A new close relative of ''Carnotaurus sastrei'' Bonaparte 1985 (Theropoda: Abelisauridae) from the Late Cretaceous of Patagonia |journal=Journal of Vertebrate Paleontology |volume=22 |issue=2 |pages=460-465 |url=http://www.bioone.org/perlserv/?request=get-document&doi=10.1671%2F0272-4634%282002%29022%5B0460%3AANCROC%5D2.0.CO%3B2}}</ref> 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 [[Gondwanaland]].<ref name=krauseetal2007/> Detailed description of known abelisaurids like ''Aucasaurus'' as well as future discoveries and analyses may help to resolve the phylogenetic picture.

==Discovery and naming==
[[France|French]] [[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''.<ref name=deperet1896>{{cite_journal |last=Depéret |first=Charles. |year=1896 |title=Note sur les Dinosauriens Sauropodes et Théropodes du Crétacé supérieur de Madagascar |language=French |journal=Bulletin de la Société Géologique de France |volume=21 |pages=176–194}}</ref> This name is derived from the [[Latin]] word ''crenatus'' ('notched') and the [[suffix]] ''-issimus'' ('most'), in reference to the numerous [[serration]]s on both front and rear edges of the teeth.<ref name=krauseetal2007/> Depéret later reassigned the species to the North American genus ''[[Dryptosaurus]]''.<ref name=deperetsavornin1928>{{cite_journal |last=Depéret |first=Charles |coauthors=& Savornin, Justin. |year=1928 |title=La faune de Reptiles et de Poissons albiens de Timimoun (Sahara algérien) |journal=Bulletin de la Societé Géologique de France |volume=27 |pages=257–265}}</ref>
[[Image:MG-Mahajanga.png|right|125px|thumb|All ''Majungasaurus'' fossils have been found in the [[Mahajanga Province]] of [[Madagascar]], most within 50&nbsp;kilometers (30&nbsp;miles) to the southeast of the provincial capital, [[Mahajanga]] (marked with a red dot on the map).]]
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]].<ref name=krauseetal2007/> 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 language|Greek]] word ''σαυρος/sauros'' ('lizard'), and made this jaw bone ([[Muséum National d'Histoire Naturelle|MNHN]].MAJ 1) the [[type specimen]].<ref name=lavocat1955>{{cite_journal |last=Lavocat |first=René |year=1955 |title=Sur une portion de mandibule de Théropode provenant du Crétacé supérieur de Madagascar |journal=Bulletin du Muséum National d’Histoire Naturelle |volume=27 |pages=256-259}}</ref> [[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.<ref name=suestaquet1979>{{cite_journal |last=Sues |first=Hans-Dieter |coauthors=& Taquet, Phillipe. |year=1979 |title=A pachycephalosaurid dinosaur from Madagascar and a Laurasia−Gondwanaland connection in the Cretaceous |journal=Nature |volume=279 |issue=5714 |pages=633-635 |doi=10.1038/279633a0}}</ref>

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.<ref name=krauseetal2007/> 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.<ref name=sampsonetal1996>{{cite_journal |last=Sampson |first=Scott D. |coauthors=Krause, David W.; [[Peter Dodson|Dodson, Peter]]; & Forster, Catherine A. |year=1996 |title=The premaxilla of Majungasaurus (Dinosauria: Theropoda), with implications for Gondwanan paleobiogeography |journal=Journal of Vertebrate Paleontology |volume=16 |issue=4 |pages=601-605 |url=http://www.vertpaleo.org/publications/jvp/contents-16-4.cfm}}</ref> 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.<ref name=krauseetal2007/>

Fieldwork in 1996 turned up a spectacularly complete theropod skull preserved in exquisite detail ([[Field Museum of Natural History|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.<ref name=sampsonetal1998>{{cite_journal |last=Sampson |first=Scott D. |coauthors=Witmer, Lawrence M.; Forster, Catherine A.; Krause, David W.; O'Connor, Patrick M.; [[Peter Dodson|Dodson, Peter]]; & Ravoavy, Florent. |year=1998 |title=Predatory dinosaur remains from Madagascar: implications for the Cretaceous biogeography of Gondwana |journal=Science |volume=280 |issue=5346 |pages=1048-1081 |doi=10.1126/science.280.5366.1048}}</ref> 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.<ref name=krauseetal2007/> This fieldwork culminated in a 2007 [[monograph]] consisting of seven [[scientific paper]]s on all aspects of the animal's biology, published in the ''[[Society of Vertebrate Paleontology]] Memoirs''. The papers are in [[English language|English]], although each has an [[abstract (summary)|abstract]] written in [[Malagasy]].<ref name=majungamemoir>{{cite_book |last=Sampson |first=Scott D. |coauthors=& Krause, David W. (eds.). |year=2007 |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=184pp |url=http://www.bioone.org/perlserv/?request=get-toc&issn=0272-4634&volume=27&issue=sp8}}</ref> 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.<ref name=krauseetal2007/>

==Paleobiology==
The abundance of ''Majungasaurus'' remains and their excellent preservation have given scientists an extremely detailed knowledge of its anatomy and allowed educated discussion of other aspects of its biology that are not always able to be analyzed in less completely known theropods.

''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 ''[[Ceratosaurus]]'' 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 unkown. 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 (zoology)|display]] purpose.<ref name=tykoskirowe2004/> While there is variation in the ornamentation of ''Majungasaurus'' individuals, there is as yet no evidence for [[sexual dimorphism]].<ref name=sampsonwitmer2007/>

===Feeding behavior===
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.<ref name=sampsonwitmer2007/> The narrow skulls of other theropods were well-equipped to withstand the vertical stress of a powerful bite, but not as good at withstanding [[Torsion (mechanics)|torsion]] (twisting).<ref name=rayfieldetal2001>{{cite_journal |last=Rayfield |first=Emily |coauthors=[[David B. Norman|Norman, David B.]]; Horner, Celeste C.; [[Jack Horner (paleontologist)|Horner, John R.]]; Smith, Paula M.; Thomason, Jeffrey J.; & Upchurch, Paul. |year=2001 |title=Cranial design and function in a large theropod dinosaur |journal=Nature |volume=409 |issue=6823 |pages=1033-1037 |doi=10.1038/35059070}}</ref> In comparison to modern [[carnivora|mammalian predators]], most theropods may have used a strategy similar in some ways to that of long- and narrow-snouted [[canid]]s, with the delivery of many bites weakening the prey animal.<ref name=vanvalkenburghmolnar2002>{{cite_journal |last=Van Valkenburgh |first=Blaire |coauthors=& [[Ralph Molnar|Molnar, Ralph E.]] |year=2002 |title=Dinosaurian and mammalian predators compared |journal=Paleobiology |volume=28 |issue=4 |pages=527-543 |url=http://paleobiol.geoscienceworld.org/cgi/content/abstract/28/4/527}}</ref>

Abelisaurids, especially ''Majungasaurus'', may instead have been adapted for a feeding strategy more similar to modern [[felid]]s, 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 [[mineralization|mineralized]] out of the [[skin]], creating the characteristic rough texture of the bones. Especially in ''Majungasaurus'', 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. The teeth of ''[[Allosaurus]]'' and most other theropods were curved on both front and back edges, a design which allowed them to slice quickly through flesh. Abelisaurids like ''Majungasaurus'' had teeth curved on the front edge but straighter on the back (cutting) edge, which may have served to prevent slicing and instead hold the teeth in place.<ref name=sampsonwitmer2007/>

''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.<ref name=sampsonwitmer2007/> ''Majungasaurus'' tooth marks on ''Rapetosaurus'' bones confirm that it at least fed on these sauropods, whether or not it actually killed them.<ref name=rogersetal2003>{{cite_journal |last=Rogers |first=Raymond R. |coauthors=Krause, David W.; & [[Kristina Curry Rogers|Curry Rogers, Kristina]]. |year=2007 |title=Cannibalism in the Madagascan dinosaur ''Majungatholus atopus'' |journal=Nature |volume=422 |issue=6931 |pages=515-518 |doi=10.1038/nature01532}}</ref>

===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.<ref name=rogersetal2003/> Suggestions that the [[Triassic]] ''[[Coelophysis]]'' was a cannibal have been recently disproven, leaving ''Majungasaurus'' as the only non-avian theropod with confirmed cannibalistic tendencies.<ref name="nesbittetal2006">{{cite_journal |last=Nesbitt |first=Sterling J. |coauthors=Turner, Alan H.; Erickson, Gregory M.; & Norell, Mark A. |year=2006 |title=Prey choice and cannibalistic behavior in the theropod ''Coelophysis'' |journal=Biology Letters |volume=2 |issue=4 |pages=611-614 |doi=10.1098/rsbl.2006.0524}}</ref>

It is unknown if ''Majungasaurus'' actively hunted its own kind or only [[scavenger|scavenged]] their carcasses.<ref name=rogersetal2003/> However, some researchers have noted that modern [[Komodo monitor]]s 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''.<ref name=roachbrinkman2007>{{cite_journal |last=Roach |first=Brian T. |coauthors=& Brinkman, Daniel T. |year=2007 |title=A reevaluation of cooperative pack hunting and gregariousness in ''Deinonychus antirrhopus'' and other non-avian theropod dinosaurs |journal=Bulletin of the Peabody Museum of Natural History |volume=48 |issue=1 |pages=103-138 |url=http://www.peabody.yale.edu/scipubs/abstracts/abs_b48-1b.html}}</ref>

===Pathology===
A 2007 report described [[pathology|pathologies]] in the bones of ''Majungasaurus''. Scientists examined the remains of at least 21 individuals and discovered four with noticeable pathologies.<ref name=farkeoconnor2007>{{cite_book |last=Farke |first=Andrew A. |coauthors=& O'Connor, Patrick M. |year=2007 |chapter=Pathology in ''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |editor=Sampson, Scott D.; & Krause, David W. (eds.) |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=180-184 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282007%2927%5B180%3APIMCTA%5D2.0.CO%3B2}}</ref> While pathology had been studied in large [[Tetanurae|tetanuran]] theropods like [[allosaurid]]s and [[tyrannosaurid]]s,<ref name=rothschildtanke2005>{{cite_book |last=Rothschild |first=Bruce |coauthors=& [[Darren Tanke|Tanke, Darren H.]] |year=2005 |chapter=Theropod paleopathology: state-of-the-art review |editor=[[Ken Carpenter|Carpenter, K.]] (ed.) |title=The Carnivorous Dinosaurs |location=Bloomington |publisher=Indiana University Press |pages=351-365 |isbn=978-0253345394}}</ref> 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 quite common. One of the specimens was a [[Phalanx bones|phalanx]] of the foot, which had apparently been broken and subsequently healed.<ref name=farkeoconnor2007/>

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 [[endochondral ossification|ossification of cartilage]] or a [[ligament]] 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 [[spinous process|neural spine]].<ref name=farkeoconnor2007/> Similar growths have been found in specimens of ''Allosaurus''<ref name=hanna2002>{{cite_journal |last=Hanna |first=Rebecca R. |year=2002 |title=Multiple injury and infection in a sub-adult theropod dinosaur ''Allosaurus fragilis'' with comparisons to allosaur pathology in the Cleveland-Lloyd Dinosaur Quarry collection |journal=Journal of Vertebrate Paleontology |volume=22 |issue=1 |pages=76-90 |url=http://www.vertpaleo.org/publications/jvp/22-076-090.cfm}}</ref> and ''Masiakasaurus'', probably resulting from the ossification of an [[interspinal ligament]] or the [[supraspinal ligament]].<ref name=farkeoconnor2007/>

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 an articulation or attachment to another 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 [[necrosis|necrotic]] and falling off. This is the first example of tail truncation known in a non-[[avian]] theropod dinosaur.<ref name=farkeoconnor2007/>

==Environment==
All specimens of ''Majungasaurus'' have been recovered from the Maevarano Formation in the province of Mahajanga 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 [[radiometric dating|radiometrically]], evidence from [[biostratigraphy]] and [[paleomagnetism]] suggest that they were deposited during the [[Maastrichtian]] [[faunal stage|stage]], which lasted from 70 to 65 Ma (million years ago). ''Majungasaurus'' teeth are found up until the very end of the Maastrichtian, when all non-avian dinosaurs [[Cretaceous–Tertiary extinction event|went extinct]].<ref name=rogersetal2007>{{cite_book |last=Rogers |first=Raymond R. |coauthors=Krause, David W.; [[Kristina Curry Rogers|Curry Rogers, Kristina]]; Rasoamiaramanana, Armand H.; & Rahantarisoa, Lydia. |year=2007 |chapter=Paleoenvironment and Paleoecology of ''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |editor=Sampson, Scott D.; & Krause, David W. (eds.) |title=''Majungasaurus crenatissimus'' (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar |series=Society of Vertebrate Paleontology Memoir '''8''' |pages=21-31 |url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282007%2927%5B21%3APAPOMC%5D2.0.CO%3B2}}</ref>

Then as now, Madagascar was an island, having [[plate tectonics|separated]] from the [[Indian subcontinent]] less than 20 million years earlier. It was drifting northwards but still 10–15[[Degree (angle)|°]] 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]] [[Channel (geography)|channels]].<ref name=rogersetal2007/> 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 proceeding dry season and providing for their exceptional preservation as fossils.<ref name=rogers2005>{{cite_journal |last=Rogers |first=Raymond R. |year=2005 |title=Fine-grained debris flows and extraordinary vertebrate burials in the Late Cretaceous of Madagascar |journal=Geology |volume=33 |issue=4 |pages=297-300 |doi=10.1130/G21036.1}}</ref> 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 (ocean)|marine]] environment.<ref name=rogersetal2007/>

Besides ''Majungasaurus'', fossil taxa recovered from the Maevarano include [[fish]], [[frog]]s, lizards, snakes,<ref name=rogersetal2007/> seven distinct species of [[crocodylomorph]]s,<ref name=krauseetal2006>{{cite_journal |last=Krause |first=David W. |coauthors=O'Connor, Patrick M.; [[Kristina Curry Rogers|Curry Rogers, Kristina]]; Sampson, Scott D.; Buckley, Gregory A.; & Rogers, Raymond R. |year=2006 |title=Late Cretaceous terrestrial vertebrates from Madagascar: implications for Latin American biogeography |journal=Annals of the Missouri Botanical Gardens |volume=93 |issue=2 |pages=178-208 |url=http://www.mbgpress.info/index.php?task=id&id=11002}}</ref> five or six species of [[mammal]]s,<ref name=krauseetal2006/> the possibly flighted [[dromaeosaurid]] ''[[Rahonavis]]'',<ref name=forsteretal1998>{{cite_journal |last=Forster |first=Catherine |coauthors=Sampson, Scott D.; Chiappe, Luis M.; & Krause, David W. |year=1998 |title=The theropod ancestry of birds: new evidence from the Late Cretaceous of Madagascar |journal=Science |volume=279 |issue=5358 |pages=1915-1919 |doi=10.1126/science.279.5358.1915}}</ref><ref name=makovickyetal2005>{{cite_journal |last=Makovicky |first=Peter J. |coauthors=Apesteguía, Sebastian; & Agnolín, Federico L. |year=2005 |title=The earliest dromaeosaurid theropod from South America |journal=Nature |volume=437 |issue=7061 |pages=1007-1011 |doi=10.1038/nature03996}}</ref> the noasaurid ''Masiakasaurus''<ref name=sampsonetal2001>{{cite_journal |last=Sampson |first=Scott D. |coauthors=Carrano, Matthew T.; & Forster, Catherine A. |year=2001 |title=A bizarre predatory dinosaur from the Late Cretaceous of Madagascar |journal=Nature |volume=409 |issue=6819 |pages=504=506 |doi=10.1038/35054046}}</ref> and two [[titanosauria]]n sauropods, including ''Rapetosaurus''.<ref name=curryrogersforster2001>{{cite_journal |last=Curry Rogers |first=Kristina |authorlink=Kristina Curry Rogers |coauthors=& Forster, Catherine A. |year=2001 |title=The last of the dinosaur titans: a new sauropod from Madagascar |journal=Nature |volume=412 |issue=6846 |pages=530-534 |doi=10.1038/35087566}}</ref> ''Majungasaurus'' was by far the largest carnivore and probably the dominant predator on land, although large crocodylomorphs like ''[[Mahajungasuchus]]'' and ''[[Trematochampsa]]'' might have competed with it closer to water.

==References==
{{reflist}}


==External links==
==External links==
*''Majungasaurus'' [http://home.myuw.net/eoraptor/Ceratosauria.htm#Majungasauruscrenatissimus entry] in [http://home.myuw.net/eoraptor/Home.html The Theropod Database].
* http://commcgi.cc.stonybrook.edu/artman/publish/article_1090.shtml
*''Majungasaurus'' [http://www.paleograveyard.com/majungatholus.html skull images] at [http://www.paleograveyard.com/main.html The Grave Yard].
* http://www.dinosauria.com/dml/names/dinom.htm
*[http://commcgi.cc.stonybrook.edu/artman/publish/article_1090.shtml Press release] about the mount of ''Majungasaurus'' mount at SUNY - Stony Brook.



[[Category:Ceratosaurs]]
[[Category:Ceratosaurs]]

Revision as of 07:19, 3 August 2007

Majungasaurus
Temporal range: Late Cretaceous
200 pixels
Scientific classification
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Genus:
Majungasaurus
Species
  • M. crenatissimus
    Lavocat, 1955
Synonyms

Megalosaurus crenatissimus
Depéret, 1896
Dryptosaurus crenatissimus
Depéret & Savornin, 1928
Majungatholus atopus
Sues and Taquet, 1979

Majungasaurus (pronounced /məˌdʒungə'sɔɹəs/ or mah-JOON-gah-SAWR-us; meaning 'Mahajanga lizard') is a genus of abelisaurid theropod dinosaur that lived in what is now Madagascar from 70 to 65 million years ago, at the end of the Cretaceous Period. Only one species (M. crenatissimus) has been identified. This dinosaur was briefly referred to the genus Majungatholus, which is now considered a junior synonym.

Like other abelisaurids, Majungasaurus was a bipedal predator with a short snout. Although the forelimbs are not completely known, they were very short, while the hindlimbs were longer and very stocky. It can be distinguished from other abelisaurids by its wider skull, the very rough texture and thickened bone on the top of its snout, and the single rounded horn on the roof of its skull, which was originally mistaken for the dome of a pachycephalosaur. It also had more teeth in both upper and lower jaws than most abelisaurids.

Known from several well-preserved skulls and abundant skeletal material, Majungasaurus has recently become one of the best-studied theropod dinosaurs from the Southern Hemisphere. It appears to be most closely related to abelisaurids from India rather than South America or continental Africa, a fact which has important biogeographical implications. Majungasaurus was the apex predator in its ecosystem, preying on sauropods like Rapetosaurus, but is also the only dinosaur for which direct evidence of cannibalism is known.

Description

Majungasaurus was a medium-sized theropod that typically measured 6–7 meters (20–23 ft) in length, including its tail.[1] Fragmentary remains of larger individuals indicate that some adults reached lengths of more than 8 meters (26 ft).[2] There has been no published estimation of its mass, although its 8–9 meter (26–30 ft) relative Carnotaurus has been estimated to weigh 1500 kilograms (3300 lb).[3]

The skull of Majungasaurus is exceptionally well-known compared to most other theropods and generally similar to that of other abelisaurids. Like most 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 (upper jaw bone), making the tip of the snout very blunt, was also typical of the family. However, the skull of Majungasaurus was markedly wider than in other abelisaurids. All abelisaurids had a rough, sculptured texture on the outside faces of the skull bones, and Majungasaurus was no exception. This was carried to an extreme on the nasal bones of Majungasaurus, which were extremely thick and fused together, with a low central ridge running along the half of the bone closest to the nostrils. A distinctive dome-like horn protruded from the fused frontal bones on top of the skull as well. In life, these structures would have been covered with some sort of integument, possibly made of keratin. Computed tomography (CT scanning) of the skull shows that both the nasal structure and the frontal horn contained hollow sinus cavities, perhaps to reduce weight.[2] The teeth were typical of abelisaurids in having short crowns, although Majungasaurus bore 17 teeth in both the maxilla of the upper jaw and the dentary of the lower jaw, more than in any other abelisaurid except Rugops.[4]

The postcranial skeleton of Majungasaurus closely resembles that of Carnotaurus and Aucasaurus, the only other abelisaurid genera for which complete skeletal material is known. Majungasaurus was bipedal, with a long tail to balance out the head and torso, putting the center of gravity over the hips. Although the cervical (neck) vertebrae had numerous cavities and excavations (pleurocoels) to reduce their weight, they were robust, with exaggerated muscle attachment sites and ribs that interlocked for strength. Ossified tendons attached to the cervical ribs gave them a forked appearance, as seen in Carnotaurus. All of these features resulted in a very strong and muscular neck. Uniquely, the cervical ribs of Majungasaurus had long depressions along the sides for weight reduction.[5] The humerus (upper arm bone) is the only preserved bone of the forelimb, but it was short and curved, closely resembling those of Aucasaurus and Carnotaurus. This may indicate that Majungasaurus had similar very short forelimbs with four digits. The hindlimbs of all abelisaurids were stocky and short compared to body length, but the tibia (lower leg bone) of Majungasaurus was even stockier than that of its relative Carnotaurus. 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.[6]

Classification and systematics

Majungasaurus is classified as a member of the theropod clade Abelisauridae, which is considered a family in Linnaean taxonomy. Along with the family Noasauridae, abelisaurids are included in the superfamily Abelisauroidea, which is in turn a subdivision of the infraorder Ceratosauria.[1][7] Abelisaurids are known for their tall skulls with blunt snouts, extensive sculpturing on the outer surfaces of the facial bones (convergent with carcharodontosaurids), atrophied forelimbs (convergent with tyrannosaurids), and stocky hindlimb proportions, among other features.[8]

As with many dinosaur families, the systematics (evolutionary relationships) within the family Abelisauridae are confused. Several cladistic studies have indicated that Majungasaurus shares a close relationship with Carnotaurus from South America,[7][8] while others were unable to firmly place it in the phylogeny.[9] 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 Gondwanaland.[1] Detailed description of known abelisaurids like Aucasaurus as well as future discoveries and analyses may help to resolve the phylogenetic picture.

Discovery and naming

French 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.[10] 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.[1] Depéret later reassigned the species to the North American genus Dryptosaurus.[11]

All Majungasaurus fossils have been found in the Mahajanga Province of Madagascar, most within 50 kilometers (30 miles) to the southeast of the provincial capital, Mahajanga (marked with a red dot on the map).

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.[1] 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 ('lizard'), and made this jaw bone (MNHN.MAJ 1) the type specimen.[12] 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.[13]

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.[1] 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.[14] 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.[1]

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.[15] 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.[1] 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.[16] 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.[1]

Paleobiology

The abundance of Majungasaurus remains and their excellent preservation have given scientists an extremely detailed knowledge of its anatomy and allowed educated discussion of other aspects of its biology that are not always able to be analyzed in less completely known theropods.

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 Ceratosaurus 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 unkown. 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.[8] While there is variation in the ornamentation of Majungasaurus individuals, there is as yet no evidence for sexual dimorphism.[2]

Feeding behavior

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.[2] The narrow skulls of other theropods were well-equipped to withstand the vertical stress of a powerful bite, but not as good at withstanding torsion (twisting).[17] 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.[18]

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. Especially in Majungasaurus, 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 joints between certain bones that allowed a high degree of flexibility in the lower jaw, although not to the extent seen in snakes. 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. The teeth of Allosaurus and most other theropods were curved on both front and back edges, a design which allowed them to slice quickly through flesh. Abelisaurids like Majungasaurus had teeth curved on the front edge but straighter on the back (cutting) edge, which may have served to prevent slicing and instead hold the teeth in place.[2]

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.[2] Majungasaurus tooth marks on Rapetosaurus bones confirm that it at least fed on these sauropods, whether or not it actually killed them.[19]

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.[19] Suggestions that the Triassic Coelophysis was a cannibal have been recently disproven, leaving Majungasaurus as the only non-avian theropod with confirmed cannibalistic tendencies.[20]

It is unknown if Majungasaurus actively hunted its own kind or only scavenged their carcasses.[19] However, some researchers have noted that modern Komodo monitors sometimes kill each other when competing for access to carcasses. The lizards will then proceed to cannibalize the remains of their rivals, which may suggest similar behavior in Majungasaurus.[21]

Pathology

A 2007 report described pathologies in the bones of Majungasaurus. Scientists examined the remains of at least 21 individuals and discovered four with noticeable pathologies.[22] While pathology had been studied in large tetanuran theropods like allosaurids and tyrannosaurids,[23] 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 quite common. One of the specimens was a phalanx of the foot, which had apparently been broken and subsequently healed.[22]

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 ossification of cartilage or a ligament during development, but the cause of the ossification was not determined. Hypervitaminosis A and bone spurs 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.[22] Similar growths have been found in specimens of Allosaurus[24] and Masiakasaurus, probably resulting from the ossification of an interspinal ligament or the supraspinal ligament.[22]

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 an articulation or attachment to another 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.[22]

Environment

All specimens of Majungasaurus have been recovered from the Maevarano Formation in the province of Mahajanga 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 Ma (million years ago). Majungasaurus teeth are found up until the very end of the Maastrichtian, when all non-avian dinosaurs went extinct.[25]

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 seasonality in temperature and rainfall. Majungasaurus inhabited a coastal flood plain cut by many sandy river channels.[25] Strong geological evidence suggests the occurrence of periodic debris flows through these channels at the beginning of the wet season, burying the carcasses of organisms killed during the proceeding dry season and providing for their exceptional preservation as fossils.[26] 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.[25]

Besides Majungasaurus, fossil taxa recovered from the Maevarano include fish, frogs, lizards, snakes,[25] seven distinct species of crocodylomorphs,[27] five or six species of mammals,[27] the possibly flighted dromaeosaurid Rahonavis,[28][29] the noasaurid Masiakasaurus[30] and two titanosaurian sauropods, including Rapetosaurus.[31] Majungasaurus was by far the largest carnivore and probably the dominant predator on land, although large crocodylomorphs like Mahajungasuchus and Trematochampsa might have competed with it closer to water.

References

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