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Re: Greg Paul is right (again) - observational analysis and phylogenetics



(Sorry, I wrote this message a while back, but never sent it... so the
thread is a little "stale".)


Jason Brougham <jaseb@amnh.org> wrote:

> In my mind cladistics is an effort to develop a system that is as explicit, 
> quantitative, rigorous, revisable, and repeatable as possible. In my opinion 
> the criticisms of cladistics - such as the assertion that
> cladistics is vulnerable to errors caused by homoplasy - goes double for 
> other methodologies, which usually resort to the best judgment of the worker, 
> rather than anything repeatable or revisable by
> better methods. Rigorous methods rescue us from the days when one 
> paleontologist says that Archaeopteryx's femoral head is rotated anteriorly, 
> and another expert says it isn't, and then that's that.


It also rescues us from the days when purely intuition-driven
evolutionary scenarios ruled.  This was particularly prevalent when it
came to reconstructing the evolution of birds.  GSP still essentially
adopts this approach, in (for example) deriving therizinosaurs from
_Jeholornis_-like ancestors, oviraptorosaurs from _Sapeornis_-like
ancestors, and deinonychosaurs from _Archaeopteryx_-like ancestors.
That one phylogenetic analysis (Xu et al., 2011) recovered
_Archaeopteryx_ as a basal deinonychosaur does not actually vindicate
this wholly intuitive approach.


Personally, I suspect therizinosaurs evolved from forms very similar
to _Ornitholestes_: small head, downcurved mandible, weakly heterodont
dentition, short metatarsus (leading to rather poor cursorial
abilities).  In fact, one day in the future _Ornitholestes_ may well
be recovered as a basal therizinosaur.  Similarly, compsognathids may
well turn out to be basal alvarezsaurs (or to put it another way,
alvarezsaurs will turn out to be derived compsognathians), which is
another hunch of mine.  However, current phylogenies do not back up
either hypothesis.  So although I might think my hunches are correct,
phylogenetic analysis remains the final arbiter.  If future analyses
do in fact show _Ornitholestes_ to be closest to therizinosaurs, or
compsognathids to be closest to alvarezsaurs, then it's not for me to
claim credit on either score.





Cheers

Tim