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Re: Brooding over dinos



Tom Hopp wrote:
>    None of what you said (above) refutes the fact that wing-feather brooding
>IS widespread among modern birds and therefor must, parsimoniously, be viewed
>as ancient and basal. 

I am not arguing that.  I am arguing whether it was a driving force in their
evolution.  If it was always present but ancillary to the main selective
forces
driving wing evolution, its age would have little or nothing to do with its
importance.  And all evidence from modern birds shows is that - at most -
it is
basal to Neornithes.  And there is still the possibility that so basic a
behaviour could be re-evolved many times with little genetic shift involved,
parsimony or no parsimony.  It is not much  more parsimonious to say "a lot of
(but not all) birds do it so it must be basal" than to say "a lot of birds in
diverse lineages don't do it, so it must be independently acquired in each
lineage".

In addition, the nesting Oviraptor comes at the issue
>from the other side: theropods DID put their breasts on their nests and
>surround their offspring with their arms.  Thus, brooding with the arms in
>theropods is a fact.

To be precise, ONE taxon of theropods is known to have adopted such a posture
AT THE MOMENT OF DEATH in what may have been extraordinary circumstances.  It
is certainly possible - perhaps even likely - that that the posture was (a)
used regularly by Oviraptor and (b) was shared with other theropods, but that
is an extrapolation, not a fact.

  Whether feathers were involved is the inference we are
>discussing.  In the face of Caudipteryx and Protarchaeopteryx, whose feathers
>are prefectly suitable for covering an Oviraptor-style nest, but not for
>flying, you may maintain your arguing position if you want, but there are
more
>and more arrows pointing in the direction of my and Mark Orsen's proposal
that
>brooding was central to it all.

I have not read your paper, but I confess I fail to see what they are.  Could
you be specific, if you don't mind my asking?  I would think you would need to
establish the following at least:

1. Brooding was widespread in theropods;

2. At least some brooding theropods (that is, KNOWN to brood) had (or, on
phylogenetic grounds, can be assumed to have had) feathered arms;

3. Locomotor hypotheses for wing (or feathered arm) evolution are untenable (I
know many have argued this, but I am still not entirely convinced);

4. Of the known non-locomotor hypotheses for the evolution of such structures,
brooding is the only tenable one (in the face of, I submit, evidence from
living birds that this is not the case with them).

>P.S. Regarding your first point (above) my speculation is that modern
>flightless birds can let their wings shrink because their sterna and breasts
>are MUCH larger than those of Oviraptor, and can cover a larger nest area or
>more/larger chicks.

My admittedly limited references say very little about the sternum in
Oviraptorids (beyond the note in The Dinosauria, which adds that sternal
material is known for only a few species).  However, I am unaware of any
research on living birds showing that sternum size or configuration correlates
with differences in brooding behaviour, or that among flightless birds
there is
a reverse correlation between sternal size and wing size.  Perhaps such
evidence exists; I would be curious to see references.

As far as Caudipteryx is concerned, to me its most striking feature is not the
feathering on the arms but the tail-flag - and I still cannot think of any
reasonable explanation for its presence other than display.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@inforamp.net