Re: Opisthocoelicaudia (was Re: Titanosaurids)

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

Tim wrote:

>(1) "Skid-like" chevrons have a wider distribution within the Sauropoda
than
>just the diplodocoids, _Mamenchisaurus_ and "shunosaurines".  Their purpose
>may not have been to "prop up" the sauropod into a bipedal (or "tripodal")
>stance (I don't ever recall that purpose being attributed to the forked
>chevrons).  One suggestion is that they protected the underside of the tail
>if it came into contact with the ground.

Alright, maybe the forked chevrons were not used for propping up, but this
does not immeadiatly mean that the point I made about the reduced chevrons.
Because of it's stiff tail, Opisthocoelicaudia wasn't able to contact the
ground, leaving the specially adapted chevrons useless. If something is
useless in nature, look at the example of the monkey-tail, it gets reduced
and eventually get lost. It isn't something rare in nature, flightless birds
did the same, the lost their power to fly because their wings became to
short to provide any lift.


>(3) Several papers on sauropod phylogeny published in the last few years
>have presented a very strong case for assigning _Opisthocoelicaudia_ to the
>Titanosauridae.  There's a lot of common features in the appendicular
>skeleton - don't get distracted by that weird tail.  Relevant authors
>include Upchurch; Wilson and Sereno; Calvo and Salgado; and others.
>
And again, if you read the post more closely, it's not just the tail I was
talking about, it also concerns the sacral vertebrae: "titanosaur-sacra have
a extra dorsosacral in their formation, but when you look at Opisto-guy
here, he included a caudal vertebrae in it's sacrum! Totally different
configuration=totally different
ancestry!" That was a quote from me for the record. The appendicular
bone-similarities can be due to convergence, since it isn't uncommon that
different type of animals get the same external appearance, but based on a
different internal design. Look at Sabertoothed cats and Thylocosmilus, or
sharks, tuna and dolphins, or even Deltadromeus and Afrovenator (both big
theropods, but both from a totally different stock)
>
>>That's pretty mean, there was on OPUS dinosaur it was possibly able to
>>dive into the water, could this be one the things you know?
>
>Tracy's lips are sealed!  :-)  By the way, what's this "diving dinosaur"
you
>mentioned?
>
D. Bensen has a picture of a diving Archaeopteryx on it's website, I think
you were a little confused, the segment was on Archaeopteryx. Diving
dinosaurs are probably something we could only fantasize about untill some
evidence has come to light. We already got the dinosaurs to swim, to make
them dive is a totally different story. :)
>
Rutger Jansma