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Re: Validity of *Suchomimus*
Appologies to those who recieve this twice, or thrice: I had some
difficulty with the Mailer Daemon when I tried to send it out earlier.
Marco Mendez wrote:
<Sereno does write this in the description of _S. tenerensis_ :
"However, no distinguishing features or proportions are apprent to us
or to prevous authors, who attributed the premaxillae to an
undeterminate species of Baryonyx. Therefore we regard C. lapparenti as
a nomen dubium">
This is without consideration of what makes *Cristatusaurus*
indistinctive or indifferential from other spinosaurid premaxillae
(*Baryonyx*, *Irritator* [sensu *Angaturama*], and *Spinosaurus
maroccanus* have premaxillae to compare) which is largely how you
determine a _nomen dubium_. The premaxillae are distinctive, in the
position and size of the alveoli (medium, large, large, diastema,
medium, medium, diastema, small, small) in *Baryonyx*, *Suchomimus*,
and *Cristatusaurus*. The premaxillae in *Baryonyx* are unfused, but
those of *Suchomimus* are partially fused, with a midline crest that
is low and robust; *Cristatusaurus* is known from two sets of
premaxillae, one unfused and eroded at the crest, the other completely
fused with a high, narrow crest. I cannot differentiate the premaxillae
based on criteria of longirostrine vs. oreinorostrine or brevirostrine,
prescence of a crest, position and shape and number of alveoli, or
ventral curvature of the premaxillae. The holotype snout of
*Suchomimus* is indifferential from that of *Cristatusaurus,* unless
you observe other differences? Teeth microtexture, for instance, may
distinguish them, or denticle size and position.... Taquet and Russell
do not elaborate, and I have to check Taquet (1984) and Kellner and
Campos (1996) who also described these premaxillae.
<...that Taquet (1984) described two fragements from the Gadoufaoua
formation of Niger ( MNHN GDF 365 and 366). It also states that each
of these fragments are identical to the premaxillae of _Baryonyx
walkeri_, the only difference is the premax teeth ratio 6/7 (_B.
walkeri_) to 7/7(in MNHN GDF 365 and 366). Although younger in age,
both these fragments (premaxillae) are reffered to Baryonyx sp.
These are the type and paratype for *Cristatusaurus*, and they differ
in two degrees from *Baryonyx*, as Taquet and Russell demonstrated when
they raised the form to a genus: hook-shaped premaxillae when viewed
from the side, midline crest.
These may be ontogenetic; if so, they are indistinguishable then
from *Suchomimus* as well, for they exhibit the same range, and
*Suchomimus* lacks autapomorphies to distinguish itself from either
*Baryonyx* or *Cristatusaurus* except robustity of elements, and this
is not considered a valid criterion, as demonstrated by Holtz, 1994,
Holtz, 1995 in his analysis of Tyrannosauridae and Coelurosauria
(robusticity is size related, see also Carr, 2000, and the most robust
known theropod specimen, Sue, which is the largest tyrannosaur known).
<Although MHNH GDF 365 and 366 are not complete enough to compare. I
think that the holotype for _S. tenerensis_ is a subadult, so i think
it gets bigger. the body lenght is about 36-feet.>
If you were to put the premaxillae of the larger type specimen of
*Cristatusaurus* on *Suchomimus*, which is 17% longer but 12% lower,
one might arrive at as high as 42.5 feet (~13 metres) or as low (the
mean of the high and low percentiles is 5%) as 38 feet (11.6 metres)
long, in *Suchomimus*, before the premaxillae fuse completely. There
are ontogenetic differences here, I'm sure, becuase the premaxillae
are not fully fused and neither are the vertebrae. But one does not
corrollate vertebral fusion and premaxillary fusion as a maturity
marker, and Brochu (1999) suggested using braincase fusion as relative
to theropods and crocodiles, to indicate maturity. This has been done
for ankylosaurs for decades.
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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