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



<GSP1954@aol.com> wrote:

> This is the kind of criticism/question I like because it is a valid issue.
> Here's how it works from my end. I have long advocated that all Cretaceous
> theropods (deinonychosaurs, therizinosaurs, oviraptorosaurs) sporting
> assorted flight adaptations are neoflightless for a variety of logical 
> reasons I
> won't repeat here. I have so far dismissed cladistics because they risk
> producing misleading results due to a lack of sufficient fossil taxa to
> sufficiently test alternatives especially when lots of functional reversals 
> occur when
> an old lifestyle is returned to. Sure enough, as the fossil data base
> expands cladistic studies are increasingly supporting parts of my hypothesis. 
> So
> of course I tend to go for those results.


Your argument, in a nutshell, is that when a certain critical mass of
fossil discoveries is reached, the "correct" evolutionary picture
becomes clear.  At this point, your hypothesis is vindicated.


However, your argument is really just circular reasoning.  You only
deem a phylogeny to be "correct" when it agrees with your conclusions.


In order for the "neoflightless hypothesis" to be a real hypothesis,
it has to be testable.  One's own intuition, regardless of how
well-founded, is not a suitable method for testing.


> I predict future discoveries will further verify the neoflightless hypothesis.


But if it doesn't... is the neoflightless hypothesis therefore
refuted?  Or will you you return to the "we need more fossils" caveat?


> But as Dan C pointed out we are
> likely never to fully be able to settle the issue for the obvious reasons.


I'm not so pessimistic.  Remember that the "neoflightless hypothesis"
is not just phylogenetic; it's also ecomorphological.  You claim that
allegedly secondarily flightless taxa (deinonychosaurs,
therizinosaurs, oviraptorosaurs) are "sporting assorted flight
adaptations", when in fact this is based on your assumptions on what
qualifies as a "flight adaptation".  Individual features that are
employed for powered flight in modern birds might originally have
evolved for a purpose unrelated to flight.  This is undoubtedly true
for postcranial pneumaticity, the furcula, the first feathers (or
their ancestral homologs), elongation of the forelimbs, and (probably)
the fused semilunate carpal.  It may well be true for many other
"avian" features: pennaceous/bipinnate feathers; enlarged sternum;
quill-knobs; strongly bowed metacarpal III; pygostyle, etc.


Phylogenetic analysis can point to the sequence in which "avian"
characters evolved.  But biomechanical studies are needed in order to
test whether an animal is anatomically competent to have been able to
fly.  For critters such as _Archaeopteryx_ and _Confuciusornis_, the
biomechanical evidence is not strong, to say the least.  Given that
(using the phylogeny of Xu et al., 2011) these taxa are positioned
near the base of their respective lineages  - Deinonychosauria and
Avialae - this undermines the entire premise of the "neoflightless
hypothesis".  That's why I'm uneasy about the whole "if it looks like
a bird, it is a bird" mantra; both _Archaeopteryx_ and
_Confuciusornis_ kinda look like birds.  But did they *fly* like
birds?  Did they fly at all?  Although we'll never know for sure,
biomechanical investigations can help rule in or out certain
behaviors, including execution of the flight stroke.





Cheers

Tim