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Re: Mesozoic roots of parrots and passerine birds



2011/8/27 Jaime Headden <qi_leong@hotmail.com>:
>
>   There are, as was said earlier, cladistic analyses that may be tested to 
> consider the jaw fragment. I've added the jaw in at one point to one large 
> analysis WAY back when, but forgot the results; I've asked Mickey to plug the 
> specimen in to some analyses, and I think Andrea Cau has plugged the specimen 
> in to his mega-matrix. My understanding is that it comes out as a bird in 
> virtually all results, and constraining it to a caenagnathid does increase 
> the quality of the analysis otherwise, or at least pushes parsimony around by 
> increasing the steps and decreasing posterior probability.

Thanks for the data. Did it result to be a parrot in these analyses,
or where there not enough number of birds? You speak of posterior
probabilities, that makes me think you used some kind of Bayesian
analysis instead of parsimony... Or do bootstrap/jackknife
probabilities used in parsimony analysis represent posterior
probabilities? I know little of Bayesian probabilities.

>   As a biomechanically-inclined individual, however, phylogenetics is not the 
> way I'd prefer to interpret the fossil initially, but rather by seeing 
> whether extreme small size (the resulting animal would be smaller than 
> *Caenagnathasia martinsoni*) will result in different jaw morphology in a 
> related animal. If it is a super-dwarf caenagnathid, we may be seeing 
> features that are related merely to that dwarfism. It may also be convergent 
> on the conditions of caenagnathids and some particular avians, but be 
> neither. It wouldn't even matter if it came from younger than the Lance and 
> was somehow reworked into the Mesozoic as this should not influence its 
> morphology or phylogeny.
>
Looks like a reasonable approach, but I think it may imply some ad hoc
hypotheses, in the form of "ifs" (as "what if they are dwarf
oviraptorids?"), and thus probably punished by parsimony in comparison
with other hypotheses. Another good approach would be an ontogenetic
one (admitting we have good representation of ontogenetic
transformations in the case of toothless neotheropods with fused
dentaries, and that the fossil is not juvenile).

Besides, congrats for your prediction that the North Slope
Pachyrrhinosaurus may have been another species!