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Re: titanosaurs



George Olshevsky (Dinogeorge@aol.com) wrote:

<Right. Ignore all the features that make Opisthocoelicaudia a
non-titanosaur and just consider those that are similar to titanosaur
features. Give the same weight to the shape of an ulna as you would to a
whole series of bifid neural spines or to a whole series of opisthocoelous
caudals. Anyone else smell a rat here??>

  What whole series of bifid neural spines? Note that bifurcation of the
neural spine occurs in more than one independant group of sauropods,
including diplodocoids and camarasaurs, where basal groups have haplocanth
spines (using *Haplocanthosaurus* and *Jobaria* as examples of basal
Diplodocimorpha as recently suggested by Wilson and Upchurch) and in
brachiosaurs and other camarosauromorphans like brachiosaurs. This tells
us nothing but that it could occur more than once, and therefore its
presence in *Opisthocoelicaudia*, as I've pointed out before on the list
in this discussion, means little. It is thus more likely to occur, if
twice, then thrice.

  Not all caudals in the series are opisthocoelous, but the middle to
distal series are amphiplatyan, and all caudals lack a ball-shaped cranial
face, but instead bear a slight expanse or flat face to the middle of the
series, a morphology which occurs in other titanosaurs including the basal
forms and some odd titanosauroids like *Tangvayosaurus*. The only constant
caudal morphology seems to occur in saltasaurines or saltasaurids where
the last sacral, first caudal, and proximal caudal series have distinct
articulating patterns (opisthocoelous and small, biconvex, and procoelous
with prominent caudal balls, in that order).

  The ulna is a distint titanosauriform morphology, and does not occur in
other sauropods, as does the neglected manus configuration; and I am still
wondering why the femur's distinct and nearly saltasaurid-only morphology
is being ignored. This is not a host of minor features; there are none, in
fact, and talking about equal weight in the quoted paragraph, I should
wonder why not? Nearly all dorsal and sacral vertebral anatomy, pectoral,
and pelvic girdles bear at least superficial shape similarities to
advanced titanosaurs, and specifically the dorsal neural arches are short
compared to centrum height with caudally-inclined, short neural spines and
relatively high diapophyses (transverse processes). The caudal neural
arches in the middle series, as in titanosauroids, are in the cranial half
of the vertebral length, and there are no pleurocoels.

  It sounds like to me that caudal "coely" and vertebral neural bifidy is
being given more weight than the remainder of the data that supports a
titanosaur affinity to at least the Titanosauria; at the point
titanosaurian affinity is recognized, the features that ally the form to
more advanced forms becomes more significant, and the finding of
*Opisthocoelicaudia* as an advanced titanosaur and occured not only to
Curry-Rogers and Forster but also to Calvo and Salgado, who have yet to
publish on their findings apart from a non-eludidating abstract in
_Ameghiniana_.

  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.

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