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Re: Tarbosaurus?



Dinogeorge wrote...
>Right, this assumes that Tarbosaurus individuals died at about the same
rate
>throughout their lives (that is, that the chance of an individual dying at
>any particular age is the same for all ages),

    But Tarbosaurus individuals probably DIDN'T die at the same rate
throughout thier lives, if juvenile mortality was numerically higher then
adult mortality, as in most animals.  If you counted up the total number of
dead juveniles and dead adults out of all the tyrannosaurs that ever lived
(NOT the total numbers that were preserved as fossils, just the ones that
died), there should be far more dead juveniles.  Its being argued that the
fossil preservation of North American tyrannosaur juveniles and adults was
more skewed with regard to representing this differential mortality then in
Asia.

>But what we really are interested in here is a function that provides the
chance of a
>Tarbosaurus fossilizing, given its age.  All other things being equal, one
>might expect the distribution of ages of fossilized Tarbosaurus to be about
>the same as that of fossilized Tyrannosaurus rex, but it is not.

     But the argument being made is that the chances of Tarbosaurus being
fosslized at a given age IS different then with North American tyrannosaurs.
We know there were differences in tyrannosaur preservation between North
America and Asia, because of the very high number of tyrannosaurs relative
to other dinosaurs in Asia.  If the distribution of al tyrannosaurs relative
to other dinosaurs can be different in North America and Asia, why not the
distribution of juveniles relative to adults?  Why just assume that "all
other things were equal" and that the proportion of juveniles and adults
preserved in Asia should be the same as in North America, when we know there
were probably other preservational biases?

>If it's Tyrannosaurus rex that has the abnormal distribution, then we
should
>be finding an occasional individual about 60 feet long--the adult of the
>subadults that we've been finding so many of lately.

    I'm arguing that Tyrannosaurus does indeed has the relative "abnormal
distribution", but in terms of PROPORTIONS of juveniles and adults being
preserved, not just absolute numbers.  We therefore don't have to assume
that the majority of the T. rexes preserved in North America are juveniles,
just because that's the way it happened in Mongolia.  The number of all
tyrannosaurs preserved relative to other dinosaurs was different, and within
the tyrannosaurs the number of juveniles preserved relative to adults could
be different too.

LN Jeff

He who stops at being better stops being good.
-Oliver Cromwell

Fear not those who argue but those who dodge.
-Marie von Ebner Eschenbach

Jeffrey W. Martz
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