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Re: Validity of *Suchomimus*



This is from a couple of days ago, sorry if the topic discussion is over,
but I thought I'd post it. 

Jaime A. Headden wrote:

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

<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.>

1 Over looking at another paper that I have, I came upon better pictures
of the specimens from Gadoufaoua MHNH GDF 365 & 366, this paper includes
a stereopair of both specimens along with dorsal and right lateral views
of both GDF 365 & 366 [ref: A.W.A Kellner and D.A. Campos, Neues Jarhb.
Geol. Palaeontol. Abh. 199, pp. 151-166 (1996).] 
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). 


2 _Suchomimus tenerensis_ has a premaxillary tooth ratio of 7/7, as does
any spinosaur, including _C. lapparenti_  (except the holotype of _B.
walkeri_ which has a ratio of 6/7). Part of the _S. tenerensis_ material
consists of an articulated snout. Unfortunately, the C. lapparenti material
is incomplete. 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 this paper they distinguish both specimens; MNHN GDF 365 as the larger,
fused individual that is not as complete (premax wise). MHNH GDF 366
as the smaller, un-fused individual that contains more teeth and is not
badly eroded (the holotype).
Kellner & Campos mention teeth microstructure, they stated: "All teeth
are serrated, with five to six serrations per millimeter" 

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.

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).

<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.>

Yes, they do differ from _B. walkeri_. In lateral view, both MHNHGDF
365 & 366 seem to be hooked. Although both _S. tenerensis_ and _B. walkeri_
 do have a hooked premaxilla, it is not so greatly hooked as GDF 365
& 366. I compared the 'hookedness' in both _S. tenerensis_  and _C. lapparenti_,
it seems that _C. lapparenti_  is hooked more. I also looked at a drawing
of a snout that characterizes Spinosaurinae [Sereno et al. Fig. 4.3 
Science 282, 1298 (1998)]. It seems that such spinosaurs as _Irritator
challengeri_  has somewhat of a bulbous premaxilla, and the external
nares are set further back than in Baryonychids. Although _C. lapparenti
does not exhibit the spacious diastema that Spinosauridae exhibits, it
does have the pattern of closely packed teeth that Baryonychids have.


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.
>From looking at the dorsal view of GDF 365,  it seems as there's an elevation
of a bony ridge that leads onto the nasal, which seems to be the only
thing to resemble the crest. The external naris is anterior to the premaxilla,
it doesn't seem as if GDF 365 has enough to compare. GDF 366 does seem
to have the maxillary notch, from lateral view that is. From dorsal view,
both seem to have an extention that extends back and makes them look
like Spinosaurines (as belonging to Spinosainae. 
Note: the suture can be seen in both specimens.     

I am not so sure about the mid-line crest, I take it that is the bone
to leads to the nasal. Keller & Campos write: " No evidence of premaxillary
sagittal crest could be observed" (In reference to the eroded specimen
GDF 365)
What is known is that both specimens (GDF 365 & 366) are at different
maturity points. 

<But one does notcorrollate vertebral fusion and premaxillary fusion
as a maturitymarker, and Brochu (1999) suggested using braincase fusion
as relativeto theropods and crocodiles, to indicate maturity. This has
been donefor ankylosaurs for decades.>

I agree, fusion in the premaxilla or the vertebrae cannot be a factor
in determining maturity of an individual. As stated by Sereno: "The premaxillae,
which fuse early in growth?"  Having the fused premaxillae can only give
us a small idea of the maturity of an individual, it only takes us to
a certain point. 
I don't think that there are any braincases for spinosaurs, with the
exception of _B. walkeri_ . 




I know only of a couple of characters that separate Baryonychids and
Spinosaurines; 
I.      Number of teeth 
II.     Skull
III.    Sail height (although only known in some species, because
of incompleteness, may or may not be a set character) = neural elongations
IV.     Serrations in teeth
V.      Premaxilla shape (bulbous vs. hooked)
VI.     Location of external nostril  

Are there more? 


Thanks to all who read this. It is midnight, and I may not be correct
in somethings, but I'll do my best next time. 


<Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
Where the Wind Comes Sweeping Down the Pampas!!!!>
It is a catchy tune, very cool though. 

Happy New Year to all, and best wishes.

-Marco A. Mendez.


-- 
Marco  Mendez
spinosauroidea@onebox.com - email
(773) 377-5006 x2159 - voicemail/fax


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