Re: Regarding Phytodinosauria, Saurischia, and so forth

[jdharris@lust.isem.smu.edu (Jerry D. Harris)]

At 4:26 PM 8/13/95, Dinogeorge@aol.com wrote:
>I see nothing in your description above that would lead me to believe you
>have a THEROPOD ichnite(!), but quite a bit that would lead me to believe
>you've misidentified it as a theropod. Why do you call it a coelurosaurian?
>Why do you call it aberrant? Why is it not an aberrant ornithopod instead
>(especially with the traces of webbing)? Well, you've got the footprints and
>I don't...

        Well, I'll leave the details for the published paper, because it's
handy to see the photographs along with them, and that's difficult in this
forum!  8-)  But...the digits have the morphology of theropod toes, not
ornithopod:  they are very long and very skinny.  Typically, the larger
ornithopods have "fat" toes.  Even the larger "gracile" ornithopods, like a
large hypsilophodontid, such as _Tenontosaurus_ (really, I know, a basal
iguanodontid) have much fatter toes.  Also, none of the ornithopods has the
ultra-compact distal metatarsus these prints have -- that kind of fusion is
the domain of the theropods.  Small narrow claw marks on the ends of some
of the prints are also theropod hallmarks.

        I used the term "coelurosaurian" in quotes to indicate that I was
using the term in the old sense, meaning a much more gracile theropod than
a robust "carnosaurian" form.  Sorry if I confused anyone there.

        The impression of the first digit indicates that it was functional
in the foot (but I think the foot was still mesaxonic), and while long, it
isn't _as_ long as digits II-IV.  It would, at least, seem to indicate that
the distal end of metatarsal I was close to the distal ends of II-IV, which
is atypical for the Theropoda in general.

        I'm intrigued as to why you find the possibility of webbing to be
more in-line with ornithopods!  I'm not talking the kind of fat padding
that some people have interpreted as webbing on hadrosaurids and
iguanodontids; I'm talking duck-like webbing, except in these prints, it
only seems to go abou;t 1/3 the way up the digits, not all the way as in
ducks.  Since the tracks were found in sediments that seem to be beach-ish
(there are near-shore marine ichnofossils on the same slabs and even
intersecting with the prints!), the idea of a web-footed theropod is
intriguing.  However, the evidence for webbing is there, but hardly
conclusive proof.  A lot more prints would have to be found with similar
features to convince me further.



Jerry D. Harris
Schuler Museum of Paleontology
Southern Methodist University
Box 750395
Dallas  TX  75275-0395
jdharris@lust.isem.smu.edu
        (Compuserve:  73132,3372)

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TITLE OF A REAL SCIENTIFIC PAPER:

"South American Animals and Their Lice"

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