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RE: Tarbosaurus?



Dinogeorge (responding to "Alanosaurus sanjuanensis" Coulson) wrote:
>In a message dated 7/22/00 2:13:48 PM EST, abcoulso@unity.ncsu.edu writes:
>
><< Stating that "sedimnetation is
> sedimentation" is, to me, ignoring way too many factors. >>
>
>I'm answering emails here, not writing a sedimentology treatise.
        Is that any way to respond to a scientific challenge? You are simply
dodgeing Alan's point, which is that you CANNOT ignore the geological
factors when making paleoecological statements. If you feel unequipped to
address the sedimentological factors, perhaps you should refrain from making
generalizations about them, or about characteristics of the fossil record
which are certainly influenced by them.

><< More juvenile remains could be preserved due to lower water velocities 
>(=smaller elements not destroyed via transport), less activity of larger 
>scavengers, different population dynamics (already suggested), niche 
>partitioning between juvenile and adult individuals with juveniles in more 
>favorable habitats (preservation-wise), or myriad other reasons. >>
>
>Again, we all know about these,
        Your statements show clearly that you, at least, do not.

>but how could you tell which, if any, were 
>operating at any particular place and time to cause the observed 
>>differences< between the collection differences between Mongolian and North 
>American tyrannosaurid specimens?
        It is called "science", specifically "geology". You would gather
sedimentological data, consult the literature, and form an hypothesis. You
(and others) would then test this hypothesis using field observations and
argumentation from the literature. I don't know if you are aware of this or
not, but paleontologists spend much of their time doing things far more
involved than making up names for new genera or deciding that a particular
species should be its own genus because an extra bone is included in the
head crest. The subject of the effect of depositional systems and other
abiotic biases on the taxonomic and intraspecific representation of an
extinct fauna is addressed (if often only in passing) in a number of recent
studies. Indeed, my own research is concerned with this subject, as should
the research of any worker attempting comparison with the Late Cretaceous
fauna of the northern plains states and Canada.

>Sure, you can imagine a gazillion factors 
>that might cause preservational biases, but if you can't constrain them, 
>they're pretty much useless.
        I can imagine a gazillion factors in almost any situation in
paleontology, none of which I can constrain. Why do you think that
*biological* fators can be pinned down (so much so as to support some of the
specious hypotheses you have presented previously on the list), yet
*geological* parameters are so variable that they may be safely ignored? I'd
like to think that I haven't been wasting the last four years on nothing. I
should very much like to see you take the above statement to Peter Dodson or
Phil Currie or Tom Holtz or any one of a great number of paleontologists who
keep geologic reasoning in reserve as one of the largest monkey wrenches in
their paleontological toolkit. Certainly, NO field paleontologist is
properly equipped without a sound understanding of geology. If you would
like to explore to the other HALF of the discipline of paleontology, may I
recommend Price and Sevier's excellent textbook, _The Earth_?

><< I won't pretend to have the answer to this question. However, I
> think it is better to leave the querry open-ended, and have  a list of
> relevant factors compiled, rather than settle on a "quick 'n easy"
> conclusion that is based on such a plethora of simplifying assumptions
> that we are guaranteed to have erred. >>
>
>Not necessarily. Sometimes a simple explanation is also the right explanation.
        I find that the simplest answer is usually the one to be found in
the rocks, not the fossils. IMHO, we have been spoiled by deposits like the
Judith River into thinking that fossil colelctions are more representative
than they truly are. I believe we should always proceed from a null
hypothesis of alteration of fossil representation by sedimentary processes.
Indeed, I expect that we will someday come to accept what I have already
heard said by some, that even Judith River collections are not so
representative as they appear.

        Later,

        Wagner
--------------------------------------------------------------------------------
     Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
  "Why do I sense we've picked up another pathetic lifeform?" - Obi-Wan Kenobi