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Where angels fear to tread, etc.

     Just a couple comments on recent threads:
     1)  For persons interested in the history of absolute dating of 
     geologic intervals, I recommend Claude Albritton's splendid little 
     book, _The Abyss of Time_ (St. Martin's Press, 1986).  The 
     contribution of Arthur Holmes in compiling radiometric dates is 
     particularly noteworthy.
     2)  On the merits of relying upon published illustrations/descriptions 
     of fossils as opposed to going to see specimens for yourself, let me 
     put in my $0.02 based on my own experimence as somebody who relies 
     mainly upon measurements of specimens for the kind of research I do.   
      When necessary, I do use published data or illustrations of fossils 
     in extracting measurements.  However, I have learned that not 
     everybody measures specimens the same way, using the same protocols 
     and anatomical reference points--and seldom  do publications explictly 
     describe how measurements were made.  Consequently if I were to 
     compile a table of published data on, say, pedal phalanx lengths of a 
     variety of dinosaur taxa, there would be some uncertainty about how 
     much variability within/across taxa is actually due to real 
     variability, and how much is due to variability in measurement methods 
     among different researchers.  If I try to measure the length of a 
     phalanx from a drawing or a photograph, I worry about whether I'm 
     getting bogus numbers due to the way the specimen was drawn or 
     photographed.  So whenever possible, I like to measure the specimens 
     myself, so that I can be sure that they were all measured the same 
     This kind of problem is even worse for the other kind of dinosaur 
     fossil I routinely measure, fossilized footprints.  A print isn't a 
     fixed anatomical structure like a phalanx or a femur, but rather the 
     record of the interaction of an anatomical structure with a 
     sedimentary substrate.  Very often what a footprint looks like in a 
     photo depends on how the photo was made, and what a print looks like 
     in a drawing depends on how the artist sees the print.  Drawing a 
     dinosaur footprint is freuently as much an exercise in interpretation 
     as in documentation.  This doesn't necessarily mean that the person 
     who originally made and published a drawing was a twit or a knave.  It 
     simply means that it is necessary for me to convince myself that I can 
     "see" in the footprint the same things that the original describer 
     did.  Furthermore, for both footprints and bones a photograph or a 
     drawing may not adequately capture the three-dimensional shape of the 
     original.  Consequently I always like to see the actual footprint, or 
     at least a cast thereof, when I try to interpret its anatomy.