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

[David Peters <davidpeters@att.net>]

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