Titanosaurs and their relationship to Brachiosaurs and Diplodocoids.

[Mike Lima <taradosgon@yahoo.com>]

>From what I've read (online) Titanosaurs were once
thought to be more closely related to Diplodocoids
than Brachiosaurs. But now they are grouped under
Macronaria with the Brachiosaurs. What led to the
change? I remember asking (and having someone
referencing a paper) about restorations in which
Nemegtosaurus had a more Brachiosaurid skull.  My
understanding is that Rapetosaurus however had
dorsally located nares and that Titanosaurs in general
had dentition more closely resembling that of a
Diplodocid. Outside of this characteristics such as
posteriorly oriented neural spines on the dorsal
vertebrae, a "wide-gauge" gait, procoelus caudals, and
crescent shaped sternal plates aren't useful because
they differentiate Titanosaurs from both groups. And
then characteristics like simple chevrons and unsplit
neural spines aren't useful because Rebbachisaurids
possess these traits as well (maybe I am wrong on that
though)? Aside from the absence of a ungual claw
(which I read was reduced in Brachiosaurids) I haven't
read of anything that connects Titanosaurs and
Brachiosaurids (but I acknowledge that this is
probably due to poor sources). What finding led the
revision of the classification of Titanosaurs?

Also, is the absence of a ungual claw a defining
characteristic of Titanosaurs or not. I found a post
from a couple years back (made by Mickey Mortimer I
believe) in which all that defining characteristics
were listed and I don't believe the absence of a claw
was on it. Is this a more recent discovery? Or is it
not a characteristic present in all Titanosaurs?


                
__________________________________ 
Yahoo! FareChase: Search multiple travel sites in one click.
http://farechase.yahoo.com