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Spinosaur Variation



Good Morning!

  I guess it's the best time to bring this up, so that
we can pick the pace up a little. (It's a pity there
aren't more non-theropod discussions going, but we
take what he can get.)

  Aside from the sail-back variation in various
spinosaurs, with Bary being the wimp of the group and
Spino the most flamboyant theropod _ever_, the fact
that a more southerly spinosaur should have a shorter
sail than a more northerly one should have something
to say on the radiator/billboard debate. Spinosaurs
typically really wouldn't need to display in threat,
being the biggest around. The rarity of fossils other
than teeth in Africa for these critters would suggests
a relative low density population any given area.
Gadoufaoua was certainly more populous spinosaur-wise
than Baharija (Egypt) or the Tafilalt and Kem Kem
(Morocco), yet we have only one good specimen. Very
wet, temperate, very like the southern US in summer at
its more agreeable times. The north was both cooler
and more forested, being able to support giant
titanosaurs as well as bigger spinosaurs and
carnosaurs/abelisaurs/whateverosaurs. This suggests a
less radiating role in the function of the sail. Of
course, Sucho was still not full-grown, like Bary, so
we do not really know the full development of the
sails.

  Meanwhile, while theropods around the Jurassic and
earliest Cretaceous were playing with sails, we have
some unsual cranial variation within spinosaurs, and
this brings me to my original purpose for this post.

  *Spinosaurus'* lower jaw suggests the animal had a
short, relatively stout cranium. It was certainly
deeper relatively than other spinosaurs known. The
length of the dentary, at 2ft, suggests that skull was
little more than 3ft long in total, perhaps a meter at
most, and this was shorter than Bary's estimated skull
length, especially as an adult (around 3.5ft, as
reconstructed using Sucho as a guide).

  *Baryonyx* and *Suchomimus* are considerably alike,
and have the very long, shallow jaws that can be used
to compare Spino's in approximating a complete
mandibular reconstruction, and from that, building a
cranium to fit, using (again) Bary and Sucho as
guides. These two were the most croc-like of the
bunch, with the sigmoid curvature of the upper jaw
being quite swung in front.

  *Cristatusaurus* (Taquet and Russell, 1998) had a
jaw nearly identical to *Baryonyx*, as Sereno et al.
1998 suggested but did not go into detail about, but
there is a significant difference between the two, in
that the "adult" specimen of the premaxilla [holotype]
has a midline ridge (not a crest) that suggests the
nose had a very long nasal crest. Similar to
*Angaturama*, but again, not a crest, it was too
broad. This suggests that Cristatu is at least a new
species, rather than being a nomen dubium. It may be a
subjective junior synonym of *Baryonyx,* but *C.
lapparenti* is distinctive enough (including fused
premaxillary suture at a size comparable to Bary's
type) to become another species of Bary (*B.
lapparenti*?) or even Sucho (which would susume Sereno
et al. into Cristatu, and *S. tenerensis* is the
subjective).

  _Anyway_, Taquet, 1984, and Taquet and Russell,
1998, described a set of jaws (upper and lower) as the
latter paper refered them to *Spinosaurus* (*S.
moroccanus*), but failed to mark a distinction in
their size. The premaxillae are almost a foot long,
larger than Sucho by about 200%, and the whole upper
jaw fragment measures nearly two feet, with a
maxillary anterior process; but the fragment's shape
and very shallow depth shows that the external naris
would either have been very slit like and long, or
been posterior to the fragment, adding about a foot
more, and ... well, to cut it short, I estimate the
skull of this animal (again, using the above
comparisons and guides) to be about 2.2m (~7ft)!

  *Irritator* and *Angaturama* are probably the same
species, though no comparative fossils are known, but
it is unlikely that they are the same specimen as
previously suggested on the list. Nonetheless,
*Irritator*'s skull appears to have been crushed
posteriorly, making the rear of the skull very
fragmentary, even the quadratojugal is missing, and
the quadrate is anteriorly displaced, being upswept
into the orbital space. Additionally, the nasals have
been dorsally eroded or broken off, and there's a
process posterior to the orbit and crest that is
probably the paroccipital process or squamosal, and
this suggests the skull is much longer than Martill et
al. illustrated. The lower jaw also appears to have
been at least partially ventrally displaced. And
that's my personal observation. Total, the skull, if
sticking *Angaturama*'s snout on front, would make the
skull around 3ft long. Meanwhile, the crest is
extended posteriorly over the orbit, and anteriorly
nearly to the snout-tip, highest anteriorly and [most]
posteriorly.

  So, there you have it. Aside from the indetirminate
tooth taxa *Asiamericana* and *Sinocoelurus,* that's
how my own perceptions fit. I've just finished a
series of profiles on these spinosaurs, relatively
sized, and will get it scanned in as soon as possible.

  Meanwhile, keep on fishin'!

===
- Greek proverb: "Knowledge is Inherent;
  Stupidity is Learned." -

Jaime A. Headden

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