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Measuring Morphological Distance


In my younger, naive days, I proposed this question for the FAQ:

        Just how similar are related dinosaurs?  Obviously
        this is a very vague question, but here's an example:
        if we could see them in the flesh, might a
        Tyrannosaurus rex and a Gorgosaurus libratus look sort
        of as similar to each other as a lion and a tiger do?
        Or perhaps T. rex and T. bataar are as alike as lions
        and tigers, and together they are as similar to the
        various Gorgosaurus species as lions and tigers are
        to, say, leopards and jaguars?

        Moving further back down the tree, no-one who is
        remotely familiar with extant mammals would ever
        confuse, say, a lion with a wolf, even though they are
        both members of the order Carnivora.  Would it be
        similarly true that no-one would ever confuse the
        theropods Tyrannosaurus and Allosaurus?

To which I got a lot of answers largely to the effect that it was a
stupid questions (it's a fair cop :-) because the groupings (genus,
family, order, etc.) are all so arbitrary.  But as I was thinking
through this recently, it did occur to me to wonder whether anyone has
ever proposed -- or even implemented -- some objective method of
measuring how different two specimens are.

Now of course, there are all sorts of problems: incompleteness of
specimens is one, but even assuming good specimens -- say, the
complete skeletons of _Gorgosausus libratus_, represented by USNM
12814, and _Coelophysis bauri_, represented by one of the Ghost Ranch
skeletons -- is there a way of saying "These two animals at 74.5%
morphologically similar"?


 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor   <mike@miketaylor.org.uk>   www.miketaylor.org.uk
)_v__/\  "A TRUE Klingon Warrior does not comment his code!" --
         Klingon Programming Mantra