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Re: Measuring Morphological Distance



Isnt this what phenetics is all about, measuring
distance by examining all the traits, and not just
derived ones?  And isn't that what phenegrams display,
not relationship, but degree morphological similarity?
~R.

--- Mike Taylor <mike@tecc.co.uk> wrote:
> Salut!
> 
> 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"?

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