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Re: Validity of *Suchomimus*



I wrote:

<The holotype snout of *Suchomimus* is indifferential from that of
*Cristatusaurus,* unless you observe other differences?> 

Marco Mendez (spinosauroidea@onebox.com) wrote:

<Teeth, premaxilla structure, and completeness. [More to follow]

...

1 ... In this report, Kellner and Campos elaborate upon the two
premaxillae fragments from Gadoufaoua (MNHN GDF 365 & 366). They do
elaborate on its physicalities and sizes, they even provide a
stereopair of both specimens (I believe they do not make mention of the
vertebrae found along GDF 365 & 366).>

  But Taquet and Russell (1998) do, and figure two of them (there are
three) as well as the additional maxillary and dentary material.

<Part of the _S. tenerensis_ material consists of an articulated snout.
Unfortunately, the C. lapparenti material is incomplete.>

... but comparable ...

<Also, it seems that both GDF 365 & 366 are missing the anterior part
of the premaxilla, GDF 366 does seem to be complete at the point of the
maxillary notch (where the maxilla articulates). But they do not seem
to have the top part where the nasal joins the premaxilla.>

  In any spinosaur, this occurs well posterior to the maxillary
articulation, and is depressingly fragile, triangular to D-shaped in
section. It does not surprise me, anyway. Most spinosaurs as known with
this material lack this region except *Baryonyx* and *Suchomimus*, and
that of *Irritator* is badly eroded and anything dorsal to a thin strut
above the external nares is absent.

<Kellner & Campos mention teeth microstructure, they stated: "All teeth
are serrated, with five to six serrations per millimeter".>

  Not what I meant by microstructure. Just did a review of the surface
textures and form of the crowns in known spinosaurid upper dentition:

  *Baryonyx*, per Charig and Milner, 1990 [first mention] is "lightly
fluted on the lingual side" with ~7 serrations/mm. (pg. 129)

  *Suchomimus*, per Sereno et al., 1998, has "textured enamel surfaces"
(pg. 1298) which are not comparable to photos of other teeth I've seen,
but I haven't seen *Baryonyx* up close, yet. These ridges are not
flutings, but longitudinal wrinkles, and the literature is clear with
photos that fluting in spinosaurids does not correspond to little
wrinkles, but long fluted surfaces.

  *Cristatusaurus*, per Kellner & Campos, 1996, has 5-6 serrations per
millimeter [for MNN GDF 365]" (pg. 158) ... "[for MNN GDF 366] present
well developed tingitudinal ridges, which are more developed lingually
than labially. Serrations are prents on the seventh left replacement
tooth, with seven to eight serrations per millimeter. Serrations are
also weaklu developed o the basal portion of the second left tooh [of
the premaxilla]" (pg. 159) ... "In the smaller specimen (MNHN [=MNN],
GDF 366), the longitudinal ridges are comparatively well developed, but
essentially on the lingual basal poirtion of the crown ... The top part
of the seventh left replacement tooh also lacks strongly developed
longitudinal ridges" (pg. 160). Taquet & Russell, 1998, "Vertical
striations are present on the teeth of the juvenile type specimen,
although they have not been observed in GDF 365" (pg. 351).

  Spinosaurines bear longitudinal ridges, perhaps better developed than
baryonichines, and are immediately discernible in *Irritator* (see
Kellner and Campos, 1996: fig. 2B) and *Spinosaurus aegyptiacus*
(Stromer, 1915: taf. I) has very well developed and discernible ridges
and grooves, prompting the utility of these ridges to diagnose
*Siamosaurus* as a spinosaur. Who knows, may there is a Thai
spinosaur....

<I counted the number of serrations per millimeter in _Suchomimus
tenerensis_. I came up with four to five (4-5) serrations per
millimeter. Although I might be wrong, I'd have to look at more teeth.>

  I would expect the number to vary, personally, within the jaw. A mean
or the relative count rostrocaudally and top and bottom may be the best
way to count these. Anyway, Sereno et al.'s figure of the tooths gives
a variable on the 5-6 serrat./mm size, which is lower than that in
*Baryonyx* (7) as given by Charig and Milner (1990), and equal to that
of *Cristatusaurus* (5-6; see above). Again, I would caution the use of
serration density without quantifying this count in the jaws. So I
agree with the next statement, for the most part.

<Also, teeth are not always the deciding factor (solidly) to claim
species. Don't all animals have unique teeth? (I mean, with serrations
and all).>

  On premaxillary hookedness: *Baryonyx* possesses a more hooked
premaxilla in profile than other baryonychines: it is shallower
posterior to the third alveolus than at it, which is similar to the
condition in *S. maroccanus* [I really dislike Sereno et al's lumping
this species in with the type species, the jaws _do not_ match, and the
vertebrae are quite distinct] -- the longirostrine condition. This
hookedness is reduced in *Suchomimus* (MNN GDF 501) and
*Cristatusaurus* (MNHN GDF 365, 366) -- the brevirostrine condition --
where the premaxillae deepen posteriorly. Marco's statement that either
*Cristatusaurus* statement is incomplete at the maxillary does not
relate to the fossils, which bear slight sutural surfaces for the
rostral lobe of the maxilla, and the medial maxillary process of the
premaxilla is apparent in GDF 366. The ventral extent of the bone in
the anterior portion of the premaxillae are not entirely preserved,
being partially eroded, and so may have indicated more depth
anteriorly. The smaller, type specimen is more hooked in profile than
the larger one, of all things, but the larger specimen is more rugose,
and perforated by many more foramina, and the base of the nasal crest
bears a large groove and foramen, as in *Suchomimus* and *Baryonyx* --
the region is not preserved in GDF 366 or other spinosaurines.

<The _C. lapparenti_ specimens are not as complete as _S. tenerensis_
and there is no material that is complete enough to give a clear
comparison.>

  Au contraire, mon ami. Es possible. The larger specimen is virtually
identicle to *Suchomimus,* and in any case that the holtype cannot be
referred, the referred snout can. There are no differences, except of
the spacing of the alveoli, that I can discern. Even the secondary
palate is identical, while it is smooth in *Irritator* and deeper
posteriorly in *Baryonyx*. In any even, the holotype is closer in
morphology to *Suchomimus* than t *Baryonyx*, and morphology is not as
distinct as is being suggested, when individual variation has not, in
my opinion, been taken into account. The published paper on
*Suchomimus* gives no reasons to supplant *Cristatusaurus* or reduce
its affirmation as a valid taxon. This is what they (Sereno et al.)
should have done. This could have been stated in the back, as was done
in that paragraph for "Spinosaurus B" being knocked into
*Carcharodontosaurus* -- reasons where listed by comparison to other
taxon. Pick up the paper and "Ahhh..., I see his point." You can only
wonder why *Cristatusaurus* was simply discarded as a _nomen dubium_.
This is why clarity in describing and reducing taxa should be handled
with the utmost care.

<I know only of a couple of characters that separate Baryonychids and
Spinosaurines;>

  I think quantifying the skull characters will have to wait until
*Irritator* is fully described. The bulbous vs. hooked may be better
discarded, as seen above: *Baryonyx*' premaxilla is more similar to *S.
maroccanus* than to *Suchomimus* or *Cristatusaurus*. Teeth of course
are serrated vs. not serrated, but some basal spinosaurine may come
along and say "Look Ma! I got *Ceratodus* stuck in my serrations!" Sail
height is really equivocal, Sucho has a taller sail than Bary, and the
*S. aegyptiacus* has one even taller. Relative density of teeth in the
lower jaw is also equivocal because no spinosaurine has both a lower
jaw and an upper that both bear teeth; *Cristatusaurus'* lower jaw may
have less teeth than *Baryonyx*, but this is very dubious without a
more complete jaw. Primary characters are in the teeth, I would think,
until more complete spinosaurines are known. I also need to get the
*Baryonyx* monograph to compare *Spinosaurus'* vertebrae....  


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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