Re: Tarbosaurus?

[Dinogeorge@aol.com]

In a message dated 7/24/00 5:59:14 PM EST, abcoulso@unity.ncsu.edu writes:

<< We're very real, we're the ones trying to factor in the real world, rather 
than totally ignore the depositional context the tyrannosaur assemblages are 
found in. If you want a reason for the bias in juvenile preservation, the 
sedimentology should be the first thing you investigate, rather than the 
first thing you gloss over >>

No, the first thing that one should investigate is the possibility of 
behavioral or other factors that would influence the ratio of subadults to 
adults living in a particular depositional locality. The principal variable 
that governs the ratio of fossilized subadults to adults at a locality has to 
be the ratio of subadults to adults in the original population. I would say 
that this variable >overwhelms< the effects of all the other variables and 
sedimentological factors, etc., particularly because subadults and adults are 
not that different in size and bone structure. All the other factors may 
modify this ratio, but they must start with the original population. 
Certainly local sedimentology and geology will affect whether or not an 
animal will be fossilized at a particular time and place, but that is >not< 
what I'm discussing.

If, for example, soil acidity preferentially removes subadults from the local 
fossil record, then there will indeed be fewer subadults than adults, as in 
the Hell Creek; but then you have to explain what kind of soil would >retain< 
subadults preferentially to adults, which is what we have in the Nemegt. And 
then you have to go to the Nemegt and to the Hell Creek, where there are 
probably a dozen different kinds of paleosol deposits in each locality, try 
to figure out what the original soil acidity might have been in each place 
where a skeleton was excavated, and see whether these data fall into line 
with your hypothesis. (They probably won't, by the way; nature has a way of 
doing that.)

Then you have to do this for all the other sedimentological variables that 
you have come up with. In the end, I think you'll come up with just what I've 
been saying: that none of these variables is as important to understanding 
the ratio of subadult to adult Nemegt and Hell Creek tyrannosaurids as is the 
original ratio of subadults to adults in their respective populations. If 
you'd like to prove me wrong, I'd be most interested in reading the results 
of your field trips to Mongolia and Montana.