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Re: Livezey and Zusi's big bird morph analysis [...]

Michael Habib (mhabib5@jhmi.edu) wrote:

<Good question.  The reason why I find it dubious is that the foot-propelled
diving characters in question don't actually align that well between the two
taxa on closer examination.  The incorporation of the femur into the body wall
is accomplished in a different fashion in the two clades, the swimming stroke
is quite different between the two (and produces very different stresses at the
proximal limb), the webbing differs very substantially, etc.  In other words,
if grebes and loons are indeed sister taxa, then it appears (to me, at least)
that  only a few characters related to semi-aquatic living would be
synapomorphies for the grebe/loon clade; most of their diving specializations
would still fall as convergent.>

  Ah, Mike, but there's the rub: Does the analysis reflect this depe level of
distinction in the morphology? Or does it only broadly reflect the features?
The explicitness of the characters or their states are the key to some
high-content analyses, and lack of clarity or consistency in resolution of any
distinction for the sake of similarity (or the reverse) easily confuses the
amount of truly shared features, conflating them or reducing them.

  This lack of explicitness is what needs to be resolved, and this tends to be
ignored when critics of the analysis surface, since they do not know the
situations or how to solve them instead of the oft-stated "add more data!"
refrain. Enforcing the quality of your own data, even if it reduces the
characters, states, or taxa, or increases them beyond one's perceived limit,
should be the first step in constructing an analysis. It's one of the reasons
I've noteven attempted to showcase one of my one full on analyses so far,
because even looking at one bone and all it's variation (say, the humerus) one
can arrive at a plethora of distinct states among similar animals (say,
segnosaurs or oviraptorids) that provides substantial resolution. It's
time-consuming work, and takes a dedicated worker to trudge through, not
someone busy attempting to fill his CV by lots of hashed and rehashed similar


Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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