BASALMOST AVES

["Matthew Troutman" <m_troutman@hotmail.com>]

Thanks to all who helped me with the cat thing.  That is really the only 
mammal group that I have not really looked into. (I'm really not as bad 
with them as I seem to be.)  Now if anybody who has helped me with the 
cat thing needs help with birds, bats, flying lemurs (anything except 
felids :)) ask me.  

<<AFAIK, this has *NOT* been demonstrated (not that it can be). There 
have been arguments as to whether _Archaeopteryx_ *could* be ancestral 
to later birds. The latest view I read (Sereno 1997) stated it was 
possible. As recently discussed on this list, there are criteria for 
hypothesizing that an animal is ancestral to others. AFAIK, these 
criteria are debated in the case of _Archaeopteryx_. Even if the 
criteria are met, we have no way of knowing that it is indeed THE (most 
recent) common ancestor, much less A common ancestor, of later birds. 
Has this changed?>>

I agree that _Archaeopteryx_ is not THE avian ancestor.  I'm just saying 
that in terms of completeness and knowledge of the animal, it is 
currently the closest thing that we have to a good idea of an avian 
ancestor.  Even Larry Martin concedes this to a POINT (emphasis on 
point).  There is a small group of workers (which includes L. Martin) 
who think that _Archaeopteryx_ is not directly ancestral to any "higher" 
avian group, they think that the only group that _Archaeopteryx_ is 
ancestral to is the Enantiornithes.  However, as Jon Wagner can tell 
you, this group has never been subject to a rigorous cladistic analysis 
(take Hou et al. 1996 in November Science, a poor analysis). 

<<Closest is a difficult concept. "Avian ancestor" is as well. If Aves
is defined as == {_Archaeopteryx_ + Neornithes}, by definition, no bird 
can be more or less closely related phylogenetically to the common 
ancestor than is _Archaeopteryx_. If Aves == {Ratitae + Tinamoui + 
Neognathae}, in which case _Archaeopteryx_ isn't even an avian, many 
many birds are closer to the common ancestor than is _Archaeopteryx_.>>

Yes, of course this all depends on your preferred definition of Aves.  
Padian and Chiappe (1997) in their Biological Reviews (1) paper 
preferred the former definition.  I have one problem with the latter 
definition; what about the Galliformes?  Peter Houde (1988) has 
published evidence that galliforms and tinamous are sister groups.  Does 
this mean that galliforms belong in Tinamoui or Neognathae?  (A real 
sticky question, galliforms have a neognathus palate).  

I think that the former definition of Aves (_Archaeopteryx_+Neornithes) 
at the time is the best one as so far.  We MAY have to change (yeah, 
right) our definition of Aves soon, though (now I'm talking crap)...

While on the topics of definitions, here is an interesting quote (that 
is not necessarily related to what we are talking about):

"Gautheir (1986) claimed to use recency of common ancestry, rather than 
similiarity, to determine classification-a claim with which I disagree.  
Like all phylogenetic hypotheses, his must be based on specialized 
similiarities (synapomorphies). The claim that his proposed phylogenetic 
relationships are based on recency of common ancestry is not supported 
by his methodology, which uses basic typological morphological 
assemblages.  Recency of common ancestry implies a genetic relationship 
inferred only from morphological analysis."  Tarsitano (1991); 545-546.  

(Please note that I do not necessarily share the opinions of the author 
stated above).  

<<No phylogenetic definition of Aves allows the inclusion of _Unenlagia_ 
within that taxon (given current phylogenetic hypotheses). Given the 
criteria of Gauthier, we may refer to _Unenlagia_ as a "bird", but I 
prefer to restrict "bird" to a dinosaur which flies or is descended from 
flying dinosaurs (ok, ok, George, we know how you would apply this... 
:).>>

Forster et al. (1998) in their Science paper (I forget the volume) 
consider _Unenlagia_, based on one of their cladistic analyses, to be 
allied with _Archaeopteryx_ and within Aves.  One cladogram yielded a 
_Unenlagia_, _Rahonavis_, and _Archaeopteryx clade (Sauriurae?), the 
other found the basalmost members of Aves to be _Unenlagia_, 
_Archaeopteryx_, and _Rahonavis_ in that order.

Houde, P.  Paleognathous birds from the early Tertiary of the Northern 
Hemisphere.  Cambridge, Mass.: Nuttall Ornithological Club.  

Tarsitano, S. 1991.  Archaeopteryx-Quo Vadis? In; Origins of the Higher 
Groups of Tetrapods.  

Matt Troutman

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