RE: Caenagnathiformes named 31 years ago!!

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Ken Kinman wrote:

 >    Of course, it now contains a whole lot more forms, but their avian 
>nature was recognized by Cracraft over 30 years ago.  So it seems my 
>expansion of Aves isn't all that radical a change after all.  This has 
>really made my day!!!!
 

To reiterate what Jaime said, the identification of the jaw material as
avian (neornithine, no less) was a MISidentification.  Over the past 150
years lots of fossil bits and pieces have been referred to Aves - especially
pterosaur material.  

>Anyway, I obviously won't be adopting "pygostyles" for any 
>apomorphy-based definitions, or anything else that is imprecise and >likely
to arise convergently.  The "true" semilunate seems to have >enlarged rather
suddenly (geologically speaking) between ornithomimes >and maniraptors.  

The Ornithomimosauria were regarded as the sister taxon to Maniraptora by
Gauthier (1986).  But the position of the ornithomimosaurs has shifted in
phylogenies published since then, and the absence of a semilunate carpal
block in Ornithomimosauria comes out as secondary.  Distinguishing incipient
expressions of a characters from reversals or secondary transformations can
often be a challenge; ornithomimosaurs are a case in point.

BTW, don't dismiss the possibility that the "true" semilunate carpal block
(which I take you define as enlarged so as to cap the metacarpus) evolved
more than once in theropod evolution.  The "presumption of monophyly" is one
of several potential dangers confronting the construction of apomorphy-based
definitions.  Remember the original definition of Arctometatarsalia?    :-)

>And 
>as far as I know, the semilunate is always a fused single bone in adult 
>maniraptors, but since the more primitive "semilunate" (of
non->maniraptors) is sometimes fused as well, I didn't put the word fused in
>the definition.  

The carpal configuration of _Alxasaurus_, which consists of two separate
ossifications, may throw a spanner in the works.



Tim