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RE: Tarbosaurus?



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Dinogeorge@aol.com
>
> In a message dated 7/24/00 4:12:51 PM EST, qilongia@yahoo.com writes:
>
> << Water speed has exactly the same effect on a young tarbosaur
> as it would
> on you if you slipped and fell into a Rocky Mountain or Great
> Plains river.
> Even a small one could kill you, and in the same breath,
> determine the fate
> of your bones 80 million years hence. >>
>
> OK, let me illustrate why this particular scenario would be
> irrelevant to my
> point. Water speed might indeed have some influence on whether or not an
> animal such as a dinosaur would be killed and then fossilized.
> But in order
> to affect the >ratio of subadults to adults< in a particular
> locality, you
> would have to show somehow that (1) subadult tarbosaurs were
> clumsier than
> adult tarbosaurs in the Nemegt environment, which would lead to
> more of them
> being killed and fossilized, and at the same time you would have to show
> somehow that (2) adult tyrannosaurs were clumsier than subadult
> tyrannosaurs,
> which would lead to more adults than subadults in the Hell Creek.
> Since there
> is absolutely no way to get a handle on the relative awkwardness of
> tyrannosaurids, and every reason to expect that the relative
> awkwardness of
> tyrannosaurids remains pretty constant across the species and
> genera, it is
> useless to consider the speed of the water when discussing the ratio of
> subadults to adults in either locality. Is the point I've been
> trying to make
> finally emerging?

Oh, bloody hell...

Folks: IT DON'T MATTER JACK WHAT THE THINGS WERE DOING WHEN THEY WERE ALIVE!

Dead bodies are **sedimentary particles**.

Sedimentary particles behave are sorted depending on factors such as stream
discharge (velocity x area, or volume x time: same thing), particle density,
particle shape, river capacitance, etc.: different fluvial regimes will
preferentially sort out different size, shape, and density particles in
different fashion.

So forget paleobiology.  It doesn't apply here. If (Big Frellin' If, since
no one has done the studies yet!) there is a difference in sorting between
the Hell Creek and the Nemegt, it would almost certainly have more to do
with the local stream conditions, not the life habits of different taxa and
ontogenetic stages of tyrant dinosaurs.

(Okay, okay, paleobiology might have something to do with: for example,
young Asian tyrant dinos might prefer a different type of local environment
than did adult North American tyrant dinos).

And need I remind anybody again that our sample sizes are so small that the
apparent difference in population distribution (if any: would like to see it
actually plotted up...) are unlikely to be statistically significantly
different.

Anybody for moving on to a new topic, such as: hypsilophodontian monophyly:
yay or nay?

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843