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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.