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Re: Thoughts on the new Czerkas book (long)



"Thomas R. Holtz, Jr." wrote:

> Cryptovolans:

> And the biggy: is this thing a flier? I have no problem per se with volant
> dromaeosaurs.  However, how does one demonstate it?  You can't just pick up
> the specimen and toss it to see if it flies: if it does, then trilobites
> were also volant! ;-)  Mere presence of feathers, even large ones on the
> arms, might be necessary but not sufficient.  My (admittedly quick)
> measurements of the best preserved feathers they show (i.e., ones where the
> shaft and the edges are both clearly present) finds an asymmetry of only 0.9
> at best: they assert these feathers are asymmetrical but do not show
> measurements to back up their case.  Fully powered flight would require
> sufficient mobility at the shoulders, in the arms, etc.: that MIGHT be
> possible, especially in basal deinonychosaurs.  Still, the case is far from
> established, and the use of conditional words like "may" or "possibly" would
> actually strenghthen their case.

I had an interesting thought about "flying" dromaeosaurs recently (yes,
hold onto your hats - I've been thinking again!)

The juvenile Sinornithosaurus specimen NGMC 91 has feathered forelimbs.
It has been suggested by some people that such "wings" were used
primarily as display or brooding structures. However, most juvenile
animals do not develop such structures until sexually mature (lions'
manes, reptilian breeding colours, etc). So it seems that these
functions may not have been the PRIMARY usage of Sinornithosaur "wings".

Now here's the kicker. What if young dromaeosaurs could manage short
flights? The juveniles of some modern species tend to show more arborial
habits than their adult forms (from Komodo monitors to cheetahs). Could
juvenile dromies have spent more time in the trees (taking short
fluttering leaps to capture small prey like insects), and then grow out
of both habitual climbing and "flying" as adults? Sickle claws could
have gone from being climbing aids for juveniles to predatory aids in
adults. Their "wings" could have gone from flight capable structures in
juveniles to display / brooding structures in adults (much as these are
also secondary functions in birds' wings).

If dromies in general are secondarily flightless, then this could have
been a classic example of ontogeny recapitulating phylogeny.
Alternatively, fully volant avians could be pedomorphic theropods,
retaining juvenile characteristics (big heads, large eyes, flight) into
adulthood and thus being permanently volant.

-- 
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Dann Pigdon                   Australian Dinosaurs:
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://www.alphalink.com.au/~dannj/
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