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Re: PDF-request: Original description of Lagosuchus and/or Marasuchus



David Peters wrote:

"Question: for all this interest in basal dinosaurs, why has no one really
looked at this at a generic level and taken this all the way back to
Euparkeria?"

Just because it hasn't been published yet doesn't mean it hasn't been done.
Patience please.  Furthermore, early dinosaurs are a great example of why
genera are relatively meaningless and why phylogenetic analysis using
supraspecific taxa can be questionable.  This needs to be done using
specimen level terminals and done by personally examining every specimen.
This takes time.

"Why, for instance, has no one included Trialestes in cladistic analysis
along with all of its bipedal sisters? (I know "why" questions are
impossible to answer. That was more of a plea.) Sadly missing from the
literature. Grad students? Get on it!"

Again maybe this has been done and just not published.  Sorry, but if you
want faster results you are going to have to do it yourself for now. Simply
demanding grad students to do it doesn't cut it, especially since you are
the one who is explicitly questioning all of the existing hypotheses.
Better get those plane tickets because simply coding from the literature
won't work this time (never does actually).


************************************************************************
Bill Parker
Vertebrate Paleontologist
Division of Resource Management
Petrified Forest National Park
P.O. Box 2217
1 Park Road
Petrified Forest, AZ 86028
(928) 524-6228 x262


                                                                           
             David Peters                                                  
             <davidpeters@att.                                             
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                                                                   Subject 
             04/09/2010 03:07          Re: PDF-request: Original           
             AM                        description of Lagosuchus and/or    
                                       Marasuchus                          
                                                                           
             Please respond to                                             
             davidpeters@att.n                                             
                    et                                                     
                                                                           
                                                                           




For Tim W.: Caution is good. Cladograms are better. Even so, all these
traits are to be expected as you get closer to the common ancestor of birds
and crocs. Bipeds? Yes, indeedy.

For David M: (smile) So true, but let's get brave, shall we? Let's list
those genera that actually would appear on the cladogram. You're listing
ghosts. Literally. Marasuchus, might have stuck around a little longer, so
it, as a genus, is not out of the running. It's a third taxon on my list.
Science is indeed about what makes sense and parsimony is one of those
things. Taxon exclusion is what makes strange bedfellows of certain taxa.

Question: for all this interest in basal dinosaurs, why has no one really
looked at this at a generic level and taken this all the way back to
Euparkeria? Why, for instance, has no one included Trialestes in cladistic
analysis along with all of its bipedal sisters? (I know "why" questions are
impossible to answer. That was more of a plea.) Sadly missing from the
literature. Grad students? Get on it!

David Peters




 What three to five genera preceded Marasuchus in the lineage of the
 Dinosauria?

>From youngest to oldest: the MRCA of *Marasuchus* and (Silesauridae +
Dinosauria); the MRCA of that + Lagerpetontidae; the MRCA of that +
Pterosauromorpha (well, or not); the MRCA of that + Crurotarsi; the MRCA of
that + Proterochampsidae or something.
Not being a direct ancestor of Dinosauria (judging from its autapomorphies
and, given the Tanzanian silesaurid, probably its age), *Marasuchus* is not
itself in the lineage of the Dinosauria.
 Testing indicates Turfanosuchus and Trialestes are in there for
 starters.

Tell us that when your manuscript has been accepted.


 Proterochampsidae and Parasuchia often show up on lists, but with
 dorsal nares, etc. etc. etc., those don't make sense.

Science isn't about what makes sense. Science is about what is most
parsimonious.


TW wrote:

Ah yes.  _Trialestes romeri_...


What specimen(s) are you using for _T. romeri_?  Aside from the holotype
(PVL
2561), two specimens (PVL 2559 and PVL 3889) have been referred to _T.
romeri_.  The holotype (an incomplete skeleton that includes cranial
elements)
and PVL 3889 (an incomplete postcranium) have been assigned to the same
taxon
(_T. romeri_) based on the striking similarity of the forelimb elements.
PVL
2559 is a partial pes.  All three specimens were found in the same horizon.


However, PVL 3889 appears to come from a dinosaur, based on features such
as a
perforated acetabulum, inturned femoral head, and mesotarsal ankle.  It is
therefore possible that the holotype comes from a dinosaur too.
Alternatively,
the _T. romeri_ holotype is a sphenosuchian-grade crocodylomorph, and PVL
3889
is a dinosaur, and the two just happen to have uncannily similar forelimb
morphology & proportions (e.g., antebrachium longer than humerus).


So _T. romeri_ must be treated with caution when putting together an OTU.
The
hypodigm is currently uncertain.


Cheers

Tim