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Re: individual age



Bill Hinchman wrote:
>Some dinosaur fossils show growth rings within
>the structure which might be indicative of age, as in ectotherms.
        I am not positive, but haven't LAGs been observed in endotherms
which either hibernate or endure harsh seasonality as well?

        All of this is complicated by the fact that those animals showing
lines of arrested growth (LAGs) exhibit reworking of the bone which would
have exhibited LAGs developed early in life (see the bone histology material
in _The Complete Dinosaurs_ for a nice general overview).

>However, this ussumes that each ring represents one years worth of growth.
(We >are now on thin ice).
        As long as they were formed in regular time increments they are at
least minimally useful in providing an absolute (although indecipherable)
timing mechanism.

>Other dinosaur fossils do not exhibit these rings at all, 
        BRASH SPECULATION: This could perhaps be related to differences in
seasonality among localities. A. Chinsamy would be the scientist to ask.

>and others still show signs of a Haversian Canal system, a marker for
>Endothermy.
        Recent experiments suggest that this is really a marker for high
activity levels. I believe they ran some poor unfortunate lizard on a
treadmill for a very long time and observed Haversian systems in its bones. :)
        If anyone would like to repeat the ref. for this experiment, I'm
sure we'd all benefit.

>In all until the question of metabolism is settled more 
>clearly, I do not think that any estimate of age can be made based on
>clear cut evidence.  
        To be frank, I don't see exactly what metabolism has to do with it.
It is quite possible I'm just being blockheaded (it's been a long day, and
it's only noon), but I don't see why one particular metabolism or another
necessarily precludes arguments for age using LAGs. Granted, the model you
choose will affect your results, but one particular metabolic model or
another will not change the fact that some dinosaurs show LAGs. Likewise,
the absence of LAGs in some other dinosaurs does not obviate the utility of
those found in others, although it does raise important questions which
should be addressed before conclusions are drawn.
        :)
        Wagner
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    Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
        "Chimp here does the killing." - Doug Mackenzie