Re: SEGNOSAUR 2

["Jaime Headden" <jaemei@hotmail.com>]

Dinogeorge wrote:

<<<The pneumaticized basisphenoid is a segnosaur autapomorphy.>>>

I replied:
 
<<Actually, it's an *Erlikosaurus* autapomorphy, as only this genus of 
this group is known with a braincase; when a different skull pops up 
with this feature, then it becomes an autapomorphy of that next upper 
taxon which will include Erliko and "unnamed segnosaur".>>

and Dinogeorge re-replied:

<While it is possible that only _Erlikosaurus_ of all segnosaurs had a
pneumaticized basisphenoid, I hardly think that's likely. (If you're 
going to get picky like this,>

  I didn't know I was getting picky. Sorry if I was, George.

<it is even possible that the very skull we have found is the only 
segnosaur skull that ever had such a basisphenoid--a one-time mutation 
that we have chanced upon.) The kind of basisphenoid that _Erlikosaurus_ 
had is not known in any other dinosaur groups, so it is fair to call it 
a segnosaur autapomorphy even if we have only one segnosaur specimen 
that displays it.>

  The likelyhood of a segnosaur autopomorphy in this case is very 
likely, I'll agree with you. I guess I _was_ getting picky. I prefer 
pedantic, since I like stepping all over things for the sake of doing 
so. :-)

  Morphology of the cranium, as I understand it, seems to be one of the 
"one true ways" of figuring dino phylogeny. You can guess a dino's 
heritage through the braincase, such as *Shuvuuia*s distinctive occiput 
puts it as avian. Matt gave me the character, but until I actually saw 
the braincase in the paper, I wasn't convinced. Now, I am almost 
convinced. Sorry, Matt. A lot of heat on one silly little fact like I 
didn't have the paper....

  But let's get back to segnosaurs for a moment. The cranial features 
show a great deal of converging in the groups of troodontids, 
ornithomimosaurs, oviraptorids, alvarezsaurids, therizinosauroids, and 
avians. You can kind of guess where I'm going with this, but I'll stop 
short of that earthshattering proclamation (that's a different thread). 
What this suggests in that, somewhere in the distant past, mid-J or so, 
all these groups diverged from one-another, including compsognathids, 
ornitholestids, dromaeosaurids, and tyrannosaurids, all part of our one 
great big Avetheropoda and/or Maniraptoriformes grouping, and that the 
first set of groups I named are closer to each other than to the second 
(possibly) group. This does not obviate dromaeosaurs from the first 
group, by the way.

  _Now_ look who's rambling!

Jaime A. Headden

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