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Dinosaur Vocalization

     I'm currently reading through Phil Senter's 2008 paper 'Voices of the 
past: a review of Paleozoic and Mesozoic animal sounds'. So far I'm finding it 
very interesting and informative, but I have some problems with some of his 
arguments for the lack of vocalization in dinosauria. I'm not a scientist, so 
I'm hoping that others on this list can help point out some key points that I 
may have missed. The argument seems to be as follows: there is lack of 
osteological indicators for pneumatization of the humerus in non-avian 
dinosaurs and since there are osteological indicators for other air sacs in 
dinosaurs, but not for the clavicular air sac, then it is unlikely that 
non-avian theropods possessed clavicular air sacs. I think there may be several 
logical flaws with this claim: 
1. If ontogeny recapitulates phylogeny in bird embryos, then as the paper 
suggests, we may presume that clavicular air sacs evolved late in ornithodiran 
history. However, using the same reasoning, we may presume that air sacs 
evolved before they invaded the bones. Therefore, the lack of osteological 
indicators for a particular air sac is not strong evidence for its absence. 
2. There may not have been sufficient selective pressure for theropods to 
evolve highly pneumatized humeri prior to the evolution of flight. The 
forelimbs of theropods were used primarily in the acquisition of prey, so it 
may have been more beneficial for (most) theropods to retain solid furculae and 
forelimb bones. The possibility that flying pterosaurs were the only other 
archosaurian group outside aves that evolved pneumatic humeri may be evidence 
of this.
3. Since air sacs of dinosaurs probably evolved before they invaded bone, the 
ancestors of Aerosteon may have had fully formed clavicular air sacs and 
therefore a syrinx. Considering this, I find it more parsimonious that the 
common ancestor of Aerosteon and aves possessed a clavicular air sac rather 
than evolving independently in allosauroids and aves. If this was the case, 
then we may use phylogenetic bracketing to presume that most taxa between 
Aerosteon and aves may have possessed a syrinx and so may have been capable of 
avian style vocalization. 
  Those are a few things that came to mind while reading that section of the 
paper. I apologize if this subject has already been heavily addressed on the 
mailing list. 
Simeon Koning.