[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Things To Look Forward To - SVP 2005 (Mesa, Arizona, USA) - Part 2



Tim Williams (twilliams_alpha@hotmail.com) wrote:

<This makes sense: "ornithischian" teeth have been descibed from both the 
Chinle Formation (_Revueltosaurus_) and the Pekin Formation (_Pekinosaurus_).>

  While their doubt is healthy, in my opinion, and I agree with Bill Parker
that we should be so cautious in assigning such positions based on just teeth,
I am ever more worried that they are determining ornithischian identity for
teeth by restricting their diagnosis to the presence of a cingulum. I do not
think ornithischians should be bound to this, since it is likely that, given
other Triassic dinosaurs, the most basal ornithischians (i.e., those most
likely to be in the Triassic) would probably lack a dental cingulum. Thus their
teeth are, as in *Eoraptor* and *Saturnalia*, going to be both phylodont in
aspect with a constriction and mild recurvature of the crown and less than
regular denticulation. This condition appears to characterize most
"ornithischian" Triassic teeth. *Pekinosaurus* is currently known based on
especially mediolaterally compressed and unconstricted, basodistally short
teeth with odd denticles, and this is certainly enough caution to assign them
to ornithischians, or even dinosaurs for that matter.

  Similiarly, the authors are restricting non-saurischian, non-ornithischians
from dinosaurs, it seems, resulting in *Chindesaurus* as a non-saurischian
(which shouldn't be a surprise to anyone if we can think there were
non-saurischian carnivorous dinosaurs) but as long as dinosaurs equal
(Saurischia + Ornithischia) and each is the opposing stem of a node of such
formulation, neither Herrerasauridae nor *Eoraptor* are technically dinosaurs.
This may eventually push *Silesaurus* even farther from the dinosaur node, when
it comes to intermediate taxa.

  Then again, Bill, Randy, and Sterling are smart guys, so I (as in SVP, 2004)
eagerly look forward to their publications on this matter as I myself assess
many of these same taxa for another project I hope to complete at some point.

<If (as seems likely) _Protoavis_ is a chimera, which element(s) get to keep 
the name _Protoavis_?  In other words, what is the name-bearing element?  My 
guess is that the holotype (or lectotype) would be a cranial element, in which
case _Protoavis_ would probably be non-dinosaurian.>

  I hope at some point I get to present a humor-filled perspective on what I am
terming the *Protoavis* Theory (I have an even funnier title for the poster or
talk this will turn into). Chatterjee could have named his "bird" *Chimaera
protoavoides*, but that is wishful thinking.

  Chatterjee in his publications first described the type's cranium before
backing it up with the postcranium and the paratype in a subsequent
publication. The rather dinosaurian-reminiscent cranium of the holotype appears
to differ from the rest of the skull which has been used to support a
drepanosaurid affinity, and if we consider this the lectotype, I am not sure we
will be able to keep *Protoavis* out of Dinosauria. However, it may simply be a
croc skull, or something, given it's strong similarities to some sphenosuchians
and the like. With the imminent removal of *Shuvosaurus* from dinosaurs, we may
realize that what makes a dinosaur skull may be in a few details, not the whole
which Chatterjee used, to "look" like a dinosaur.

  The fact that all the material has been prepped to look complete as it was
presented doesn't help readers to determine what parts are preserved or not,
and the discussions have not help so much, either (the humerus and femur both
lack most of the diaphysis, for example, but the photographs may not show this
as clearly as his skeletal reconstruction purports to preserve material).
 
<Even _Chindesaurus_ is a coelophysoid?>

  Apparently it's non-saurischian. Of course, the caution is that these are
abstracts, not primary data, so I will wait for the detailed evidence....

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com