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Re: Tarbosaurus?



On Mon, 24 Jul 2000 Dinogeorge@aol.com wrote:
 
"> As I said before, the SEDIMENTOLOGICAL FACTORS ARE IRRELEVANT to this 
> discussion. They DON'T NEED to be addressed here. READ MY LIPS. How many 
> times do I have to point this out before it SINKS IN?? If you think they're 
> relevant, SHOW HOW, don't just SAY that they're relevant.
> 
> I claim that whatever sedimentological factors operated in the Nemegt and the 
> Hell Creek would sample the two populations the same way."

        SHOW HOW, don't just SAY they're irrelevant

 "Show me how they would not."

        OK, I'll show you mine, then you show me yours :)

" Show me how the speed or depth of the water"

        faster water can move larger skeletal elements, and move smaller
elements more readily. Thus, faster water = smaller elements are harder to
preserve in situ, or at all, as they're abraded during transport. Thus,
juvenile elements, which are smaller than adult elements, will be affected
moreso than adult elements

", the soil acidity, "

        bones can only be preserved under certain soil pH
conditions. Otherwise, they degrade. Again, smaller juvenile elements
won't take as long to disappear as equivalent, larger adult ewlements

"> rainfall,"

        this affects local soil conditions, runoff, water velocity in
local channels, the carnivore, herbivore, and scavenger fauna present, and
vegetation types

 "size of particulate matter deposited,"

        larger sediments are more likely to abarade and thus destroy small
elements than large elements. 

" etc.  would affect the >ratio 
> of fossilized subadults to adults< in a tyrannosaurid population."

        simple; if those factors are operating in such a way that
presevatin of smaller elements is less likely, the juvenile skeletons are
less likely to be preserved. If  juveniles are abnormally abundant in the
fossil record, they could have lived in environments more favorable to
fossilization than adults; such niche partitioning between old and young
is seen in some crocodilians. It's also possible that juvenile mortality
was higher in one population than another, due to the presence of other
large predators, fewer prey items, cannibalism, or Republican-controlled
daycare :) (joke)

" GET REAL, MAN!"

        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

Alan Blake Coulson
3938-C Marcom St
Raleigh NC 27606
abcoulso@unity.ncsu.edu
PhD student at North Carolina State University