Re: sauropod quantity

[Josh Smith <smithjb@sas.upenn.edu>]

At 03:51 AM 9/20/99 -0700, Jaime A. Headden wrote:
>misproportion of juvenile-to-adult ratio. These tracks
>may represent juveniles of some larger animals.

This is possible.
>
>  And how would they need be theropods? During the
>time frame suggested above (Nor-Toarc) there are
>perhaps a superabundance of non-theropods that walked
>three-toed and would have left slender-toed prints
>without impression of the hallux, including smaller
>"prosauropods" like *Thecodontosaurus*, and
>"hypsilophodontids," especially, and all basal
>ornithschians, generally.

Generally speaking, a track expert can distinguish theropods from
three-toed herbivorous dinosaurs.  The toes have a somewhat different
structure in theropods than in the other three-toed forms.  So this
possibility can be fairly well ruled out for many of these tracks


Actually, this is far from correct. Any of us who work on tracks who are
being honest with themselves and you will tell you that, especially for
the smaller tracks, this can be very difficult to do.  Much of the
morphology of tridactyl dinosaurs is basal and those differences that
are expressed (look at how many discussions of dinosaur anatomy refer to
characters distal to the tarsus--not that common) rarely show up in
footprints, which represent a degraded facsimile of the original pedal
anatomical structure.  I focused on this problem (for smaller, early
Mesozoic tracks) for my Sc.M. thesis project, and it is a huge can of worms...

Be careful of what Lockley says--he will have you inferring bloody skin
color and parental nursing habits from claw morphology...(ok, so maybe
that is a stretch...).

-Josh

Josh Smith
Department of Earth and Environmental Science
University of Pennsylvania
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240 South 33rd Street
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