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Re: Dracorex's phylogenetic position examined with science

Michael Mortimer (mickey_mortimer111@msn.com) wrote:

<First, I made a NEXUS file from Williamson and Carr's matrix.  I left
characters ordered, but altered some of the codings so as to avoid weighting
characters.  For instance, character 35 is "Parietosquamosal shelf nodes:
absent (0); present (1).", but character 36 is "Parietosquamosal shelf nodes:
absent (0); in more than two rows (1); in a single row, sometimes accompanied
by ventrolateral corner nodes (2)."  This weights the presence of
parietosquamosal shelf nodes, since their absence gets a state in two
characters.  So I changed state 0 in character 36 to inapplicable.  I also did
this for 26 vs. 21, 34 vs. 51, 41 vs. 40, 43 vs. 8, 47 vs. 46, and 53 vs. 52. 
Finally, I switched the order of states in character 47 (which describes which
end of the parietosquamosal bar is taller) to be a logical progression when the
character is ordered (medial end taller > ends subequal > lateral end taller).>

  One could potentially fix this without altering states by altering characters
to be unweighted by condensing them. Indeed, one can make a four-state
character from:

"Pairetosquamosal nodes, pattern: absent, no nodes (0); present in a linear row
{1}; present in two linear rows (2); present in more than two, irregular rows

  One can then further define the arrangement and presence of outlying nodes
(the parietosquamosal node sullivan is fond of and the "corner" node) as
additional states, but likely might be best as characters as the presence of
the corner node is essentially in the same place as an additional row of nodes
would be, and at that point there would be no point to making them linear,
since they would be a bifurcating chain of states.

  Additionally, the presence of the dome and its progression medially and
posteriorly would be unordered in an appropriate test, as Bakker et al. argues
for homoplasy. Frankly, *Dracorex* looks like a heavily spiked homalocephalid,
but that's my opinion.

  Lastly, one might attempt to merge the disparate matrices of Williamson and
Carr and that of Sullivan, as this might best capture their different coding
perceptions and give where each analysis differs in characters an attempt to
fill in some blanks. That Williamson and Carr started from scratch, and
Sullivan from a root Sereno, 1999 cladogram, though Sullivan adds characters,
might best be treated as a cohesive treatment all taxa might be coded into.


Jaime A. Headden

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

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