Re: sauropod quantity

["Jaime A. Headden" <qilongia@yahoo.com>]

Josh Smith wrote:
<<Where is this coming from, George? First of all, if
we are talking truly "chicken-sized" and
"sparrow-sized" in the Triassic and Jurassic, then we
are talking about the Norian to the, say Toarcian, ja?
If these are the ages we are discussing, then there
are not "thousands and thousands" of tracks in this 
size class. Indeed, these tracks are biased towards
the mid-range (from about 4-8 inches in track-length).
If we discuss only the Newark Supergroup ichnofauna, 
then I would doubt that there are more than a couple
hundred such tracks.>>

and Dinogeorge replies:

<Just finished reading the relevant section of
Lockley's The Eternal Trail, wherein he notes chicken-
to sparrow-size theropod tracks from Navajo Sandstone
(prints 1.5 inches long), from Connecticut, from
Newark, from Argentina, from Brazil (Botucatu Fm.).
See pp. 121-122. I believe Ellenberger has tracks in
this size range from South Africa, too. These small
dinosaurs were apparently distributed worldwide during
Late Triassic through Late Jurassic times, most
widespread during Early to Middle Jurassic.

These are not Coelophysis-size tracks but several
times smaller. The smallest dinos I can think of off
the top of my head that are earlier than Compsognathus
are Segisaurus and Procompsognathus, which might have
made the >largest< of those small theropod tracks.
There are no "sparrow-size" nonavian dinos known from
skeletal remains (maybe some teeny teeth) at all, 
period. The tracks compare in size with, but are
otherwise different from, those of small mammals found
in the same localities.>

  It is true that we know of no adult sparrow-sized
dinosaurs in the Triassic, and even through the EJ,
but around the Aves-formative years of the MJ and LJ,
certainly this is a bit anticipatory? No adults, but
juveniles, certainly, there is an abundance of. The
smaller the animal, the smaller the baby, generally,
though on occasion (as in the kiwi) there is a severe
misproportion of juvenile-to-adult ratio. These tracks
may represent juveniles of some larger animals.

  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. These tracks could pertain
to a wide range of taxa, especially in the Karoo
though later stages in the South African region, where
*Heterodontosaurus*, baby prosauropos like
*Euskelosaurus*, and *Massospondylus* (my fave) would
have roamed.

===
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

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