[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Greg Paul is right (again); or "Archie's not a birdy"



> >  In a similar vein, the supposed apomorphies of
> Pygostylia and
> >  Ornithothoraces (whose non-apomorphy-based
> definitions implicitly
> >  rest on the assumption that the supposed
> apomorphies *are*
> >  apomorphies)
> 
> No, that's not how it works. The PhyloCode, at least, is
> not concerned with such etymological implications.

True, but I was not considering etymology: if the supposed apomorphies on which 
a phylogenetic hypothesis rests turn out to be homoplasies, the clades named 
from this hypothesis are affected.

Ornithothoraces uses an enantiornithine and a neornithine. The instability of 
basal Pygostylia and the physical constraints for self-powered flight make me 
wary of whether enantis and euornis are sisters. Their shoulder and ankle bones 
evolved independently to the respective apomorphic condition. The sterna are 
different enough except for the keel. There is no reason to assume that the 
pygostyle is a synapomophy either. All this indicated that the "basal 
ornithothoracine" was barely capable of self-powered flight, if at all.

So Ornithothoraces only makes sense if the assessment that particular traits 
are apomorphies is not mistaken.

> >  seem to be homoplasies at least for the largest
> part, or even - in
> >  case of the pygostyle - hint at nonmonophyly.
> 
> The birds with a pygostyle -- as opposed to, presumably,
> the oviraptorosaurs and segnosaurs that may have one --
> clearly do form a clade, even though *Sapeornis* is outside
> Pygostylia.

They *resolve* as a clade, but this may be due to functional constraints. At 
least the set of (supposed) apomorphies originally used to unite them looks 
weak, they may all be functionally constrained. (_Sapeornis_ can be made to 
fall within "Pygostylia", FWIW)

But there is a way to test this now, based on O'Connor & Chiappe (2011) who 
didn't do any analysis but reviewed and tabulated the material: what happens if 
you only evaluate the skull, sampling paravians from the base until the loss of 
teeth on the ornithuran lineage? For all we know, the cranial skeleton was not 
much affected by the requirements for self-powered flight.


Eike