Re: Eocursor, new basal ornithischian

[William_Parker@nps.gov]

> heby@libero.it wrote:

>> Sacisaurus + Silesaurus are dinosauriforms and often referred to as
>> "putative basal ornithischians"; however this has never been fully
tested
>> in a phylogenetic analysis featuring a wide diversity of taxa (including
>> crocodile-line archosaurs as well). The characters in these taxa that
>> supposedly support a relationship with the ornithischia are based on
dental
>> characters which can be homoplastic.

>I agree, however, some possible sinapomorphies (of the hindlimbs) listed
on Ferigolo et al. (2006) and Dzik (2003) >are not used in the recent-most
cladogram of dinosauriforms, that of Langer and Benton (2006). Moreover,
this >analysis suffer of a problem: too few basal taxa as you stated(I
confess to dislike the use of a single OTUs >Outgroup instead of sequential
taxa (like Euparkeria, Proterochampsids, Lagerpeton, etc.), and the use of
>'Ornithischia' instead of various taxa like Stormbergia, Lesothosaurus,
Agilisaurus, Heterodontosaurus, >Scutellosaurus, etc. Until now no
comprehensive study has been made to compare the above listed taxa to
>'Silesaurids'.

The two hind-limb characters listed by Ferigolo and Langer (2006) as
possible synapomorphies of Sacisaurus and ornithischians have wider
distributions.  A "non-proximally expanded cnemial crest" is found in other
non-dinosaurian dinosauriforms.  A "well-developed outer malleolus of the
tibia" is also found in basal theropods and sauropodomorphs (as admitted by
Ferigolo and Langer).

I agree that all previous studies have suffered from a lack aof analyzed
basal taxa.  Several workers are now looking at this in more detail.

>Although I cannot say much, a forthcoming paper will show an intriguing
position for Silesaurus...

I am looking forward to this.

>>Are there any other characters that support a
>> Sacisaurus/Silesaurus + Ornithischia relationship to the exclusion of
other
>> dinosauriforms?

Nick Gardner actually rephrased my question more succinctly and captured
the point that I was trying to make:

      "So in actuality the question should not be just "are there any other
      characters that support a _Sacisaurus_/_Silesaurus_ + Ornithischia
      relationship to the exclusion of other dinosauriforms", but also "is
      the number of those characters greater than the number of those
      supporting the alternative placement?""

The number of characters NOT supporting the clade is much more numerous.


>Ok, but you're telling just that teeth are homoplastic.

Yes.

>Other characters, acetabulum perforation, vertebral pneumaticity, sacral
vertebral count, loss of osteoderm, and >many other are present in both
crurotarsal and dinosauromorph archosaurian, but not for this reason we
overlook >these characters. My suggestion to end this problem would be a
'super-matrix' study of Archosauriformes, >integrating even poorly known
taxa (Hallopus, Trialestes, Agnostyphis, Teyuwasu....).

Exactly what is needed!  Recent re-evaluations of purported dinosaur taxa
by Irmis et al. (2007) and Nesbitt et al. (2007) is attempting to set some
of the groundwork for this and provide alternative taxonomic hypotheses to
be tested.

>I think that the most convincing (to me) sinapomorphy is the presence of
an anterior beak on the dentary, exactly >like the presence of an Os
rostrale is sinapomorphic for Ceratopsia. Even if Silesaurus don't show any
evidence for >a separate ossification, in Sacisaurus two paired element are
where we would expect to find an unpaired predentary.

Another interpretation is that the dentary of Sacisaurus matches that of
Silesaurus in lacking this element and that the "two paired elements" are
portions of the anterior part of the dentary and that the proposed "suture"
between the dentary and "pre-dentary" is simply a groove (Irmis et al.,
2007).

 >I found very little parsimonious consider the 'proto-predentary' of
Sacisaurus only a convergence with >Ornithischian, especially when we are
looking for VERY basal and Triassic taxa with ornithischian affinities.
>However, I must admit that the anatomy of Silesaurus is not only very
basal, but also aberrant, so at present I >don't favor any hypothesis
instead of another. Although plesiomorphic in a number of traits, Eocursor
is already a >true ornithischian; its pelvic anatomy is radically modified
and derived respect to Eoraptor, Marasuchus, >Saturnalia, Herrerasaurus,
Silesaurus etc., so compare this taxon (or Lesothosaurus) to basal
Saurischian
>or Dinosauromorphs will be more complicated than we think.

I find it interesting that some non-dinosaurian dinosauriforms are
"ornithischian-like", whereas others are "sauropodomorph-like" and
"theropod-like".

>>
>> Technosaurus is possibly closely related to Sacisaurus and Silesaurus
and
>> not an ornithischian.
>>
>> Pseudolagosuchus and Eucoelophysis are dinosauriforms.

>Both Ezcurra (2006), and Nesbitt et al. (2007), have found that femoral
anatomy in these taxa and Silesaurus is >very similar, and almost unique
among dinosauromophs, so a reappraisal must be done to comprehend if these
features >are sinapomorphic for a 'silesaurid' group or not.

Agreed.  Ferigolo and Langer (2006) mention this similarity as well.

>>
>> Bromsgrovea is a ctenosauriscid poposaur closely related to
Arizonasaurus.
>>
>> Spondylosoma is non-dinosaurian and most likely a "rauisuchid".


Mh...for both Spondylosoma and Bromsgroveia there is no reported tarsal
anatomy, so any relationship must be deeply investigated.

True no tarsals are known for Arizonasaurus or Bromsgroveia, but the ilium
of Arizonasaurus is IDENTICAL to that of Bromgroveia (I excavated it
myself).  Furthermore Benton and Gower (1997) note that elongate neural
spines (from dorsal vertebrae) are also known for Bromsgroveia.
Arizonasaurus is clearly a poposaurid and it is almost certain that
Bromsgroveia is as well.

>The paper of Galton reviewing Spondylosoma and Bromsgroveia were written
before the publication of Sacisaurus and >Silesaurus, so his conclusion on
pelvic an cervical vertebrae anatomy must be taken with an open mind. Both
taxa >show similar iliac and vertebral anatomy (together with Caseosaurus)
to 'rauisuchid' and Silesaurus and Sacisaurus, >so...I confess to really
wonder which are their true phyletic relationship. At present I could only
suggest that >only further work will give us a comprehensive view of
archosaurian relationship. Many characters used to link >Bromsgroveia are
present also in dinosauromorphs, and as noted above, the peculiar iliac
anatomy suffer of >convergence between advanced 'rauisuchians' and
'silesaurids'.

The ilia of poposaurids and Sacisaurus and Silesaurus are superficially
similar but that just demonstrates the plesiomorphic morphology of those
elements in the latter two taxa.

>> Caseosaurus is based on an isolated ilium that shares character
affinities
>> with basal saurischians and sauropodomorphs.

>But also with Silesaurus: the supra-acetabular crest, which is buttressed
by the anterior iliac process, and forms >a vertical ridge coming close to
the dorsal margin of the acetabulum are features present also in Silesaurus
and >Sacisaurus, besides Plateosaurus, Efraasia (although poorly developed
in these sauropodorphs) and 'rauisuchians'.
>I wonder if this specimen could belong to Eucoelophysis....

Possible but just conjecture of course.  The holotype of Chindesaurus
bryansmalli does contain fragments of the ilium and these fragments share
will Caseosaurus a single synapomorphy, the presence of a triangular shaped
rugosity on the dorsolateral surface of the posterior iliac blade (Nesbitt
et al. 2007) thus Caseosaurus may pertain to a Chindesaurus-like animal,
which would make it a basal saurischian and not a non-dinosaurian
dinosauriform (Langer, 2004; Nesbitt et al., 2007).  Someday we will find
more of Chindesaurus to set this straight....

>Best regards,

>Lukas Panzarin

Thanks.  I am enjoying the discussion and getting away from aetosaurs for a
second.

Bill



************************************************************************
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