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Re: Origin of Birds




> I've seen a great deal in the last few weeks on the Feduccia and Jones 
> papers attacking the Maniraptoran (or other dinosaur) origin of birds.  
> Assume for a moment they're correct (unlikely as it may be).  What are 
> the alternatives?  Are there any other candidate lineages that make any 
> sense?  

      No, which a big problem with any NON-dinosaurian theory for the
origin of birds.  Some have pointed out in the that dromeosaur and
troodont remains are not known from the Early-Middle Jurassic (although
some possible teeth are now known from the Bathonian of England), while
neglecting to mention that neither is anything else even REMOTELY
birdlike; except for theropods.  They may not be the sorts of theropods we
think birds descended from, but they are a lot closer then anything the
other camp has been able to come up with.  Of archosaurs, only dinosaurs,
crocodylomorphs, and pterosaurs are known to have crossed into the
Jurassic at all.  Pterosaurs havn't been considered a viable candidate by
anyone for decades.  Crocodilians have been tied to birds by some, but
nearly all the similarities are either found in archoasuars in general or 
also found in theropods. Fairly gracile crocodilains have been
found, but they are a long way from looking bird-like.  Feduccia's own
best non-dinosaurian candidate for bird origins, the drepanosaur
_Megalanacosaurus_, looks like a chameleon with a rounded head and
a tapered snout, giving the head a superficially _Archaeopteryx_ like
appearance.  This and the fact that it appears to have been arboreal are
the only evidence I remember Fedduccia offering that it might be connected
with birds.  There were a number of small gliding forms like
_Longisquama_ and _Podopteryx_ from the Triassic, but there is no
particular similarity between thier aerodynamic  strategies and those of
birds; _Podopteryx_ used a membrane stretched between the back legs, and
_Longisquama_ used some sort of scale derivative coming off the back.           
      As far as the embryology is concerned, when evidence, or at least
interpretation of different lines of evidence differs, SOMETHING needs to
be explained away.  Either the embryological interpretations are in error,
birds altered thier embryology slightly from that of pentadactyl embryos
(keep in mind that the other embryos Fedducia looked at started out fully
pentadactyl; the chicken had already loss one digit, so development is not
identical; some modification has already taken place from the start of
development), or the dinosaur bird similarties represent the most massive
and detailed case of evolutionary convergence anyone has ever seen.  The
fossil evidence has been growing over the past few decadess, and I
don't think that most paleontologists who have studied the dinosaur-bird
connection in detail are willing to chuck all the impressive fossil
evidence out the window just yet. 
 
LN Jeff
O-