Opisthocoelicaudia (was Re: Titanosaurids)

["Fam Jansma" <fam.jansma@worldonline.nl>]

Øyvind wrote:

>regarding Opisthocoelicaudia's fused chevrons, and the other strangely
>shaped vertebrae. Couldn't it just be that the opisthocoelicaudia specimen
>we know, was a cripple? I know there are found diplodocids with entire
>vertebrae fused together due to decease.
>
Weird Opistocoelicaudia, I knew him well Horatio... Originally placed as a
subfamily of the Camarasauridae (now believed to be early members of the
Macronaria), than as a Titanosaurid, but some dude (can't remember your name
anymore, sorry) in an old post has an interesting point here:

"<<_Opisthocoelicaudia_is a derived titanosaurid, with implications in the
next paper.>> I think the cladistics is wrong here. _O._is no more a derived
titanosaurid than segnosaurs are theropods. It's much more likely some kind
of derived euhelopid or derived basal diplodocid that has picked up a few
random titanosaur-like characters here and there that are throwing off the
analyses. The caudal-vertebral articulations and dorsal vertebrae
are_completely_unlike those of titanosaurids. It's incredibly improbable
that_O._just happens to be the one titanosaurid in which the dorsal
vertebrae and caudal vertebrae simultaneously converge to a
euhelopodid/diplodocid form, particularly in view of it's biogeographical
closeness to all the other known euhelopodids"

Furthermore, look at the sacralvertebrae they also give a clue to a
different ancestry: titanosaur-sacralvertebrae have a extra dorsosacral in
their sacrum, but when you look at Opisto-guy here, he included a caudal
vertebrae in it's sacrum! Totally different configuration=totally different
ancestry! The chevrons eliminate both referall to the Chinese "Cetiosaurids"
(like Shunosaurus or Mamenchisaurus) or Diplodocid, although the option
should not be excluded. It's tail was stiffened by the reversal of it's
tailvertebrae, making it's skidlike chevrons useless for propping up on his
tail, so they possibly disolved or something. Why hanging on to something
that no purpose anymore right, the same reason man lost their tail...

Rutger Jansma