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Crocodile-eating Majungasaurus?



The hypothesis of aquatic habits for Majungasaurus, and bite marks in
a 3-4 m peirosaurid attributed to some large theropod by Fiorelli
(2010) led me wondering on reliance in crocodile-eating by this
abelisaurid. Majungasaurus was found in seasonally flooded habitats
and the proximity of streams, where the most common animals are
crocodyliforms (Rogers et al., 2007), so crocodiles may have been an
abundant resource. But, I do not know Malagasy crocodiles with
Majungasaurus bite marks, so the case of the peirosaurid does not hold
for Majungasaurus. Majungasaurus bite marks in Rapetosaurus and
Majungasaurus bones counter my hypothesis, but how representative this
is of the proportion of food ingested seems questionable, as it looks
difficult for a species to heavily rely on itself as a resource.

Sampson and Witmer (2007) hypothesized large sauropod killing through
the use of a few holding/cutting bites. To me, it seems difficult that
relatively large (adult?) sauropods would be a sustainable resource to
be exploited by a (numerically safe) Majungasaurus population in such
a small land mass as Madagascar, which was isolated from other land
masses at this time. Also, there is the argument by Michael Habib on
the possibility of dangerous damage at large size when dealing with
gigantic prey. I am speculating about Majungasaurus eating mainly prey
not thicker in cross section than its open jaws, which is suggested by
the intramandibular joint and broad mouth, both of which may help
widening the gape. I doubt cutting with axial movements as the ora,
because only the dorsal neck musculature is strongly developed, thus
suggesting enhanced strenght not for sideways movements, but for
dorsal movements.

There are some similarities with the similarly tall skulled South
American frog Ceratophrys, which swallows prey whole. The relatively
small and straight teeth, as in Ceratophrys, may just help in
swallowing whole by providing points of contact with the prey, as in
some small-toothed frogs and siluriforms which swallow prey large
relative to their heads (possibility which would make expectable the
lack of reported bite marks in Malagasy crocodiles if these were
swallowed whole - however I doubt Ceratophryis hunts cuirassed prey;
and perhaps Ceratophrys' relative Beelzebufo may have been a preferred
prey). The high skull may imply a more vaulted palate, and thus an
increased mouth cavity, useful to swallow whole prey relatively large
in comparison with the head of the predator.

The reforced epaxial musculature of the neck may help raising objects,
for example in swallowing with help of gravity like birds. The strong
epaxial musculature may have helped raising prey which is larger than
a mouthful of teared flesh; other theropods which likely teared flesh
do not have such a developed epaxial musculature. Raising of the prey
may also permit hitting it against the substrate, as in some birds
(and/or, the strong epaxial musculature may be just related to
head-butting, in which it may either help stiffening the neck if it
mostly tended to bend ventralwards at hitting, or imply some kind of
"ascending" head blow).

Citations:

Fiorelli, L. E. 2010. Predation bite-marks on a peirosaurid
crocodyliform from the Upper Cretaceous of Neuquén Province,
Argentina. Ameghiniana 47 (3): 387–400.

Rogers, R. R., Krause, D. W., Curry Rogers, K., Rasoamiaramanana, A.
H. & Rahantarisoa, L. 2007. Paleoenvironment and paleoecology of
Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late
Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir 8.
Journal of Vertebrate Paleontology 27 (Suppl. to Number 2): 21–31.

Sampson, S. D., & Witmer, L. M. 2007. Craniofacial anatomy of
Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late
Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir 8.
Journal of Vertebrate Paleontology 27 (Suppl. to Number 2): 32–102.