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Re: Majungatholus: Apparent Cannibal



George Olshevsky (Dinogeorge@aol.com) wrote:

<If they maintain that there is only one Maevarano abelisaurid, then its
name will have to be Majungasaurus crenatissimus, unless it can be shown
that the known M. crenatissimus material is indistinguishable from at
least two different genera of theropods. The situation is similar to that
of Allosaurus fragilis, whose holotype is not diagnostic but for which
diagnostic topotype  material exists. The holotype of Majungatholus atopus
does seem to be a  topotype of M. crenatissimus (they're not from
different horizons, according  to The Dinosauria), so it can be regarded
as a more diagnostic specimen of  the latter species; likewise the nice
FMNH skull.>

  Not to question the motives of any author, but so far, the UA material
is topotypic only of MHNH MAJ 4, the type of *Majungatholus atopus*. This
is because the type dentary of *Majungasaurus crenatissimus* is distinct
from that of the UA material. Specifically, the uncatalogued type of *M.
crenatissimus* shows a strong dorsal curvature of the ventral margin
reminiscent of *Carnotaurus*, whereas that of the UA material is
relatively straighter; the type of *M. crenatissimus* also bears a
distinct dorsal emargination of the lateral groove, but no ventral
embayment, whereas the opposite is true of both *Carnotaurus* and the UA
material. There is a broader ventral dental shelf than is found in the UA
material, and the jaw lacks the vertical fluting of the external surface
as is found in *Aucasaurus*, *Carnotaurus* and the UA material. The jaws
also show a general taper in the posterior third to half that, if
continued forward, are similar to *Aucasaurus*, but do not occur in the UA
material in which the dentary is much more consistently deep along its
length, and where the UA material has a distinct chin, neither the *M.
crenatissimus* jaw nor *Carnotarus* do.

  Whereas Sampson et al. were right to regard the new material as
belonging to *Majungatholus atopus*, they are not right in designating *M.
crenatissimus* as a nomen dubium and the type unworthy of receipt of any
name. It is rather diagnostic and comparable to other abelisaurid jaw
material, and implies the jaw and skull may have looked more like
*Carnotaurus* than does *Majungatholus*, and that these features imply a
closer relationship.

  I offer here that the conclusion that Rogers et al. offered, that there
is direct evidence of *M. atopus* feeding on its own species, is weaker
when considering there were, in fact, TWO taxa in the Maevarano formation
capable of dealing this level of damage. The problem is is that both
spoecimens are highly distinct in size:

  *M. crenatissimus* has a nearly complete dentary length of 183mm,
reaching from the posterior dentary process just below the surangular
fossa that the surangular articulates onto on the dorsal posterior
dentary, to the mid-height of the symphysis (a complete length would
probably be another 10mm in length, but the jaw was not likely to be any
more than 200mm in length entirely), and the spacing of the teeth was for
5 teeth every 50mm;

  In the UA material, the dentary length is about 275mm for a total jaw
length of 575mm, over twice the the size of the *M. crenatissimus* size,
with a tooth spacing of 5 crowns every 80mm or so. If scaled up to length
with the UA material, this gives *M. crenatissimus* is jaw length of about
 405mm, and a spacing of 5 crowns every 105mm. The gross disparity of
spacing is because the smaller jaw has spacing for 18 crowns (though the
measurements were taken in the posterior half of the jaw where actual
spacing is determinable, and the rostral dentary in *M. crenatissimus*
does not preserve sockets for 40% of its teeth), whereas the larger jaw
has 15. Questions of age may be answered in that the smaller jaw has fully
ossified and fused interdental plates with no traces of immaturity, though
the jaw is less rugose. These are not, based on gross anatomy, not the
same species. Problematically, the spacing issue, an apex every centimeter
in the *M. crenatissimus* jaw and more than this in the UA material
(around 1.6cm between apices of consecutive crowns), matches the spacing
on one transverse process in the Rogers et al. paper (fig. 1, e), slight
larger than on the neural spine of a caudal vertebra (fig. 1, a), and much
smaller than the spacing on a haemal arch (fig. 1, c) but not another
(fig. 1, b) where the spacing is consistent.

  In response to this, I would offer that *M. crenatissimus* is a valid
taxon, and was not conspecific with *M. atopus*, but that it may have
easily made some of the marks on the bones presented. An increase in only
30% of its size would render *M. crenatissimus* capable of making the
larger marks on *M. atopus* bones. This size increase is still merkedly
less than that size reached by the well-featured UA skull, and if smaller
jaws exist, then pardon, but the spacing of the one UA skull published
(1.6cm) gives a spacing more than that shown for the one chevron (fig. 1,
c) which shows well-spaced scoring (1-1.4cm between gouges).

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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