Re: Sheesh

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Taylor wrote:

> ALL RIGHT!  We GET IT!  We ALL UNDERSTAND that birds are dinosaurs.
>
> Now can we please -- just occasionally -- have a conversation where, when 
> someone uses the word "dinosaur" in a context where is very, very obviously 
> means "non-avian dinosaur", they are allowed to do sowithout half a dozen 
> people leaping down their throats waving their big cladistic banners?

But Mike (Taylor), Mike (Keesey) makes an excellent point. Why would you 
exclude birds from this particular context?  This has nothing to do with 
cladistics.  Birds are, and always have been, dinosaurs.  Phylogenetic 
nomenclature only presents this hypothesis more explicitly.  Saying that 
dinosaurs never became aquatic, with the caveat that by 'dinosaurs' we 
really mean 'non-avian dinosaurs', strikes me as unfair to the scope of 
dinosaur diversity.  Because yours is essentially an evolutionary question, 
the pool of taxa relevant to the discussion should include *all* descendents 
of a common dinosaurian ancestor.  IMHO.

Still, I agree with the semantic aspect of your grievance.  In retrospect, 
it might have been better if the term 'dinosaur' was limited to non-avian 
dinosaurs for vernacular usage, and a new term was erected for 
dinosaurs-including-birds (like Avedinosauria or something, analogous to 
Cetartiodactyla).  Even better, the word 'dinosaur' could be used in the 
vernacular sense, and 'dinosaurian' (noun) used in the scientific sense 
(i.e., including birds).  Although there is no paradigm shift in an 
objective biological sense in having birds-as-dinosaurs, there is certainly 
a paradigm shift in a more subjective ideological sense that is rooted in 
two centuries of Linnaean taxonomy.

Personally, I'm happy with Aves as a subset of Dinosauria; if evolution put 
them there, who am I to argue?  But I can see the confusion this 
nomenclature can cause.

Mike Keesey wrote:

> Good points. Another question to ask: why is it that only ornithurans 
> (sensu stricto), out of all pan-
> avians/avemetatarsalians*, were able to return to the water (and repeatedly 
> so)? [snip] And it isn't "birds" (whichever sense) that are the only ones 
> to have become aquatic; it's specifically (as far as we know) ornithurans 
> (node-based sense: hesperornitheans + carinates sensu stricto).

I've wondered this too.  My guess is that the ornithurans/euornitheans got 
to the water first.  Their early evolution is dominated by water-loving 
forms.  This part of avian phylogeny is chock-full of species that spent 
most of their time in or around water (_Gansus_, _Archaeorhynchus_, 
_Yanornis_, _Ichthyornis_, etc).  At least one of these lineages committed 
itself to a fully aquatic ecology (Hesperornithes) in the Early Cretaceous, 
and many fully aquatic neornithean lineages may have evolved in the Late 
Cretaceous (like penguins).

Although there are enantiornitheans that probably lived near water (e.g., 
_Longirostravis_), overall the Enantiornithes seemed to have preferred dry 
land, especially trees.

Cheers

Tim

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