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RE: A question about Mickey's non-theropod tree
I've been offlist quite long and surely missed some important points. I
took a look at the non-theropod part from HP Mickey Mortimer's site, and I
saw that Mesosauridae were tentatively put within Diapsida along with
Claudiosauridae and that Anapsida is part of Achosauromorpha. Did I really
miss some important points or is there new evidence for these taxa?
The position of Mesosauridae is based on Modesto's (1996) thesis. Based on
his restudy of mesosaurs, he found-
Modesto finds many characters supporting traditional nodes (Sauropsida,
Romeriida, Diapsida, etc.) to be problematic, indicating the topology there
isn't as certain as we usually take it to be. No surprise there, as I think
that's true of just about any morphological cladogram. However, I do take
issue with Modesto's method of objectifying quantitative characters. If he
plots taxa on a line of potential ratios for a character (e.g. humerofemoral
ratio) and sees no distinct gaps between where taxa plot, he drops the
character. This does make it more objective in a way, but it also ignores
real variation and does such when we need to use it most (i.e. when we have
a lot of intermediate taxa that need to be sorted out).
As for Anapsida being inside Archosauromorpha, that's a consequence of
molecular phylogenies finding turtles sister to Archosauria (Zardoya and
Meyer, 1998; Hedges and Poling, 1999; Kumazawa and Nishida, 1999; Rest et
al., 2003; Iwabe et al., 2005), and phylogenetic taxonomy defining Anapsida
as turtles and taxa more closely related to them than to extant saurians.
Ah, the consequences of poor definitions... when will they learn?