Re: Opisthocoelicaudia (was Re: Titanosaurids)

["Mickey_Mortimer11" <Mickey_Mortimer11@email.msn.com>]

Tim Williams wrote-

> (1) "Skid-like" chevrons have a wider distribution within the Sauropoda
than
> just the diplodocoids, _Mamenchisaurus_ and "shunosaurines".

Indeed.  Barapasaurus, Rhoetosaurus and Camarasaurus have them, while it's
unknown if brachiosaurids or Haplocanthosaurus did.  Gongxianosaurus is said
not to though, which indicates it appeared within the Sauropoda.

> (2) There is titanosaur material from South America that shows a
combination
> of opisthocoelous and non-opisthocoelous caudal vertebrae.  Considering
what
> we now know about homoeotic genes and pathways, the possibility of a
salient
> switch from a strongly procoelous --> strongly opisthocoelous condition in
> caudal centra should not be dismissed out of hand.

Specifically-

undescribed Titanosaurid (Rigal and Calvo 1999)
Coniacian-Santonian, Late Cretaceous
Rio Colorado Formation, Argentina
Material- more than 150 bones including cranial, cervical, dorsal, sacral,
caudal, pectoral, forelimb, pelvic and hindlimb material and osteoderms
belonging to three individuals (including cervicals, dorsals, caudals,
chevrons, scapula, coracoids, humerus, metacarpals, ilium, pubis and femur)
Description- The cervicals are opisthocoelous without cervicals.  The
dorsals have aliform posteriorly sloping neural spines without saltasaurid
characters.  In one specimen, three articulated middle caudals are
procoelous, amphicoelous and biconvex, while two distal caudals are
opisthocoelous and biconvex. This is completely different from the other two
specimens, but the neural arches are near identical. In the other specimen,
the caudals are mostly strongly procoelous, but some are biconcave and
biconvex.
Comments- Preliminary studies suggests this is a new species.
References- Rigal and Calvo, 1999. Unusual caudal series of Titanosauridae
of the Late Cretaceous in the Rio Colorado Formation, Neuquen and Mendoza
Provinces, Argentina. VII International Symposium on Mesozoic Terrestrial
Ecosystems, abstracts.
Gonzalez Riga and Calvo, 2001. A new genus and species of titanosaurid
sauropod from the Upper Cretaceous of Rincon de los Sauces, Neuquen,
Argentina. JVP 21(3) 55A.

undescribed Titanosauridae (Rigal and Calvo 1999)
Coniacian-Santonian, Late Cretaceous
Rio Colorado Formation, Argentina
Material- 200 disarticulated bones belonging to two individuals
Description- Most of the caudal vertebrae recovered are procoelous, but one
mid caudal is opisthocoelous.
References- Rigal and Calvo, 1999. Unusual caudal series of Titanosauridae
of the Late Cretaceous in the Rio Colorado Formation, Neuquen and Mendoza
Provinces, Argentina. VII International Symposium on Mesozoic Terrestrial
Ecosystems, abstracts.

> By the way, I thought _Nemegtosaurus_ *was* a titanosaur - in recent
> publications, only Upchurch (who puts it in the Diplodocoidea) seems to be
> holding out.

Even Upchurch wasn't firm regarding diplodocoid nemegtosaurids when I talked
to him at SVP.

George Olshevsky wrote-

> No, it was Nothronychus (before its description), which was the first
> segnosaur in which there was a preserved furcula, together with a better
> description of the segnosaur foot (Sereno, pers. comm.) than was available
in
> the literature. The furcula carries a lot of weight in theropod
systematics,
> and it was enough to push me over the line: so, segnosaurs are theropods
> convergent on prosauropods rather than prosauropods convergent on
theropods.
> If something like that turns up in Opisthocoelicaudia, I'll change my
mind.
> But right now, there's just not enough evidence that O. is a titanosaur
for
> me to alter my opinion.

Nothronychus doesn't preserve a furcula to my knowledge.  How about strongly
opisthocoelous caudal centra showing up only in titanosaurs?  Isn't that
good evidence Opisthocoelicaudia belongs there? :-)

> Oh, yes it is. There are sauropod columns with just a few bifid vertebrae
and
> there are sauropod columns in which practically all the vertebrae are
bifid.
> Each vertebra needs to be scored individually.

Just picture all the characters in my coelurosaur study- cervical 1 without
pleurocoels...... dorsal 9 with two pleurocoels....... caudal 34 without
transverse processes.  Ahhhhh!  With all of their caudals uniquely
procoelous, alvarezsaurids would be monophyletic without doubt, supported by
a Bremer index of 25 based on caudal central morphology alone!  Obviously,
such a division of characters would represent a weighting problem.  A better
solution (which many people utilize) is to have multiple states in a single
character to represent changes along the vertebral column.

Tracy Ford wrote-

> To me, it's pretty ludicrous that there is only one group of Late
Cretaceous
> Sauropods. One thing is the cladistical analysis and they are looking at
> numbers and not the actual specimens. The Diplodocid looking titanosaurs,
> are IMHO diplodocids, the Camarasaur looking titanosaurs are IMHO
> camarasaurds, etc. There is new evidence, still being worked on, that
> will...Ok, I won't be mean...

We also have rebbachisaurids (Calvo and Salgado, 1995; Novas, 1997; Lamanna
et al., 2001; Antarctosaurus in part?) and brachiosaurids (Kirkland et al.,
2000; Rauhut and Werner, 1997), not to mention questionable dicreaosaurids
(Russell et al., 1994) and diplodocids (McIntosh et al., 1992).  Plus, the
titanosaur group containing Late Cretaceous members (including Austrosaurus,
Huabeisaurus and titanosauroids proper) is a pretty big part of the sauropod
tree.  Upchurch's cladistic analyses on sauropods all use genera for OTU's,
so a priori combining Late Cretaceous taxa into a single family is not a
question.  New evidece is always interesting though....

Mickey Mortimer