Name:
Majungasaurus
(Majunga dome).
Phonetic: Ma-jung-ah-thole-us.
Named By: Ren� Lavocat - 1955.
Synonyms: Majungatholus atops,
Megalosaurus crenatissimus.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Abelisauridae, Carnotaurinae.
Species: M. crenatissimus (type).
Type: Carnivore.
Size: 6-7 meters long, some fragmentary remains
suggest 8 meters long.
Known locations: Madagascar - Maevarano
Formation.
Time period: Maastrichtian of the Cretaceous.
Fossil representation: Several skulls and post
cranial material, allowing for Majungasaurus to be reconstructed
piece by piece.
When
first discovered only the top part of the skull of Majungasaurus
was
known. This fragment revealed a dome like structure which was taken
to be indicative of a pachycephalosaur.
Further fossil material would
reveal the truth about Majungasaurus being a
carnivorous theropod,
although this was not the first time that a carnivorous dinosaur was
mistaken for a pachycephalosaur, with the same thing happening to
Troodon.
Majungasaurus
is notable among abelisaurids,
as while it shares the
same characteristic short, deep skull, it has a single small horn
that rises from the top of its skull above where the eyes would be.
In fact it was a poorly preserved spike that led to the
misidentification of Majungasaurus in the first
place. This spike has
been found to made from porous material indicating that it almost
certainly was just for show, and too fragile for combat.
The
skull is short and tall with a blunt snout and features with a
rough texture. Inside, reconstruction of the brain has revealed
that Majungasaurus that had an underdeveloped
floccus. The Floccus
controls balance coordination, and when examined along with the inner
ear structure, suggests that Majungasaurus was
not capable of sudden
or repeated side to side movements of the head. This may not have
been a a problem however as Majungasaurus is
thought to have preyed
upon larger and slower dinosaurs. The inner ear orientation has also
revealed that Majungasaurus most likely held its
head straight and
horizontal to the ground.
Another
characteristic that Majungasaurus shares with other
members of
the abelisauridae are the underdeveloped forelimbs. These also appear
puny in Majungasaurus, with the fingers fused
together. The only
possible conceivable use for such arms would be to grip another
dinosaur perhaps during mating. The flip side to the arms however are
the legs which appear to be very powerful with strong muscle attachment.
Study
of some of the vertebrae of Majungasaurus has
revealed the very
exciting possibility of a respiratory system that is very similar to
modern birds. The vertebrae are shaped to allow for the inclusion of
special air sacs that increase the amount of oxygen available for
respiration by making sure exhaled air is removed from the lungs in a
kind of one way system. This differs from respiration in humans as
inhaled and exhaled air travel though the same system meaning some
mixing between the two.
The
evolutionary implications for this discovery are quite significant
as while it is known in birds, birds are thought to have descended
from the tetanurian line of dinosaurs that includes the maniraptors of
the coelurosauria, the most direct ancestors for birds.
Majungasaurus is not tetanurian, it is
ceratosaurian, although
both groups have their origins with a common ancestral group. While
you could argue for a case of convergent evolution, the fact that
this respiratory system appears in both lines that diverged from the
same source indicates that it evolved before the split. This means
that the origin of the system was dinosaurian, not avian, and
further establishes the evolutionary link between dinosaurs and birds.
The
prey item usually referred to Majungasaurus is the
titanosaur
Rapetosaurus.
The connection between these two dinosaurs has been
made upon the grounds that not only is Rapetosaurus
the only known
large herbivore for that time and location, but also Rapetosaurus
fossils have been found with tooth marks that match the dentition of
Majungasaurus, including teeth shape and spacing
in the jaw. It may
well be that Majungasaurus specialised in large
prey like Rapetosaurus
given that its robust legs would have not allowed for great speed,
but would have provided great stability and support when tackling
large prey.
Majungasaurus
is considered to be a cannibal as well as a predator of
other dinosaurs on the evidence of Majungasaurus
fossils that show the
teeth marks that match the teeth that are found in Majungasaurus
as
well as the Majungasaurus teeth marks on Rapetosaurus
fossils. An
animal actively hunting another of its species is unlikely unless a
larger member of the species attacks a smaller one. However it is
also quite possible that the Majungasaurus in
question was simply
scavenging the remains of another of its species. Another explanation
could be a Majungasaurus killing another in
competition over territory
for the right to feed at a carcass, with the loser also being
subsequently eaten. Whatever the exact explanation, you should not
put too much stock into the claims that Majungasaurus
is the 'only'
dinosaur to be a cannibal as similar evidence can also be found for
other large theropods including Allosaurus
and Tyrannosaurus.
Further reading
- Sur une portion de mandibule de Th�ropode provenant du Cr�tac�
sup�rieur de Madagascar - Ren� Lavocat - 1955.
- The premaxilla of Majungasaurus (Dinosauria:
Theropoda), with
implications for Gondwanan paleobiogeography - Scott D. Sampson, David
W. Krause, Peter Dodson, & Catherine A. Forster - 1996.
- Cannibalism in the Madagascan dinosaur Majungatholus atopus
- Raymond
R. Rogers, David W. Krause, & Kristina Curry Rogers. - 2007.
- Overview of the history of discovery, taxonomy, phylogeny, and
biogeography of Majungasaurus crenatissimus
(Theropoda: Abelisauridae)
from the Late Cretaceous of Madagascar". In Sampson, Scott D.;
&
Krause, David W. (eds.). Majungasaurus crenatissimus
(Theropoda:
Abelisauridae) from the Late Cretaceous of Madagascar - David W.
Krause, Scott D.Sampson, Matthew T. Carrano, & patrick M.
O'Connor
- 2007.
- Craniofacial anatomy of Majungasaurus crenatissimus
(Theropoda:
Abelisauridae) from the Late Cretaceous of Madagascar". In Sampson,
Scott D.; & Krause, David W. (eds.). Majungasaurus
crenatissimus
(Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar -
Scott D. Sampson & Lawrence M. Witmer - 2007.
- Dental morphology and variation in Majungasaurus
crenatissimus
(Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar". In
Sampson, Scott D.; & Krause, David W. (eds.). Majungasaurus
crenatissimus (Theropoda: Abelisauridae) from the Late
Cretaceous of
Madagascar - Joshua B. Smith - 2007.
- The postcranial axial skeleton of Majungasaurus
crenatissimus
(Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar". In
Sampson, Scott D.; & Krause, David W. (eds.). Majungasaurus
crenatissimus (Theropoda: Abelisauridae) from the Late
Cretaceous of
Madagascar - Patrick M, O’Connor - 2007.
- The appendicular skeleton of Majungasaurus crenatissimus
(Theropoda:
Abelisauridae) from the Late Cretaceous of Madagascar". In Sampson,
Scott D.; & Krause, David W. (eds.). Majungasaurus
crenatissimus
(Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar -
Matthew T. Carrano - 2007.
- Pathology in Majungasaurus crenatissimus
(Theropoda: Abelisauridae)
from the Late Cretaceous of Madagascar". In Sampson, Scott D.;
&
Krause, David W. (eds.). Majungasaurus crenatissimus
(Theropoda:
Abelisauridae) from the Late Cretaceous of Madagascar. - Andrew A.
Farke & Patrick M. O'Connor - 2007.
- Paleoenvironment and Paleoecology of Majungasaurus
crenatissimus
(Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar". In
Sampson, Scott D.; & Krause, David W. (eds.). Majungasaurus
crenatissimus (Theropoda: Abelisauridae) from the Late
Cretaceous of
Madagascar. - Raymond R. Rogers, David W. Krause, Kristina Curry
Rogers, Armand H. Rasoamiaramanana & Lydia Rahantarisoa. - 2007.
- Abelisaurid forelimb evolution: New evidence from Majungasaurus
crenatissimus (Abelisauridae: Theropoda) from the late
Cretaceous of
Madagascar - S. Burch & M. Carrano - 2008.
- Case 3487: Megalosaurus crenatissimus Dep�ret, 1896 (currently
Majungasaurus crenatissimus; Dinosauria, Theropoda):
proposed
replacement of the holotype by a neotype. - The Bulletin of Zoological
Nomenclature. 66 (3): 261–264. - Matthew T. Carrano, David W. Krause,
Patrick M. O'Connor & Scott D. Sampson - 2009.
- An articulated pectoral girdle and forelimb of the abelisaurid
theropod Majungasaurus crenatissimus from the Late
Cretaceous of
Madagascar. - Journal of Vertebrate Paleontology. 32 (1): 1–16. - S. H.
Burch & M. T. Carrano - 2012.
- Ontogenetic changes in the craniomandibular skeleton of abelisaurid
dinosaur Majungasaurus crenatissimus from the Late
Cretaceous of
Madagascar. - Acta Palaeontologica Polonica. 61. - Patrick O’Connor,
Nirina Ratsimbaholison & Ryan Felice - 2016.
- Paleopathology in a nearly complete skeleton of Majungasaurus
crenatissimus (Theropoda: Abelisauridae). - Cretaceous
Research. 115:
104553. - Samuel B. Gutherz, Joseph R. Groenke, Joseph J. W. Sertich,
Sara H. Burch & Patrick M. O’Connor - 2020.