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Re: My Thoughts on Limusaurus' hand
There is a proximal dorsolateral process on metacarpal III in
coelophysoids and Limusaurus, similar to one on metacarpal II in some
basal tetanurines like Guanlong. Yet Guanlong also has a process on
metacarpal III, which partly covers metacarpal IV, even though the latter
is not illustrated in Xu et al.'s paper. Acrocanthosaurus and Allosaurus
also have a processes on metacarpal III, while "Szechuanoraptor" lacks
processes on metacarpals II or III. This process on metacarpal III of
tetanurines could be homologous to the process on III in basal theropods
as easily as it could the process on II.
*Limusaurus* can also be said to have such a process on mc II. At least it
looks that way in the cross-section drawings the supp. inf. provides.
Xu et al. ran a phylogenetic analysis which determined that when
characters states are ordered, the resulting tree assuming tetanurines
have digits II-III-IV-V is six steps longer than if they are assumed to
have digits I-II-III-IV. The length of the unordered trees is equal, but
leaving characters unordered potentially leads to ridiculous "intermediate
synapomorphies" like coelophysoids and Herrerasaurus being diagnosed by
having a single phalanx on digit IV (not more or less) or taxon being
diagnosed by having an intermediate ratio, as opposed to relatives with
low and high ratios.
This is a very important point: potentially continuous or meristic
characters must be ordered (Wiens 2001).
Furthermore, neither Xuanhanosaurus, "Szechuanoraptor" or Megaraptor were
included in their matrix
Wow. I didn't even notice.