Re: Ornithodira, breathing with long necks

["Jerry D. Harris" <dinogami@hotmail.com>]

Matt (and others)wrote:

> > "Pressurized cervical, humeral, and femoral air sac diverticula in living
> > avians function as passive stay devices for their respective extremities 
> > and
> > some may have had similar functions in saurischian dinosaurs."

> I have never heard this before ?????  However,:

  That's because no one ever noticed it before; it's the gist of Akersten's 
work.  IOW, and to quote Dr. Holtz, "WAIT FOR THE PAPER."  8-P

> So, birds DO have a nuchal ligament, it is just divided into many separate
> parts that do the same thing.

  A series of interspinous ligaments is, fundamentally and structurally, a 
very different thing than the mammalian nuchal ligament, even if the final 
result (support of the neck) is similar -- let's not confuse the issue by 
stating "it's the same but different."  It's just "different."  Sauropods 
have a variety of features for neck support that are lacking in birds and 
mammals; the obverse is true, too.  This is something I am working on at 
present (sadly, again, this must be a "WAIT FOR THE PAPER" situation...)

> Again, I have not heard of this in bird necks.  Did anyone on the list go 
> to
> this talk/poster?  Did they show anything convincing regarding the
> bird/air-sac/neck thing?

  Akersten's work is certainly novel and interesting, but has a few 
problems to overcome.

  To address the problems some others have raised:

  There are two cervical air sac "groups" in bird necks: one that runs 
_inside_ the vertebrae, through the vertebral canal, along with the spinal 
cord, and a second that runs alongside the vertebrae, through the transverse 
foramina, along with the vertebral artery and vein.  The former is 
surrounded entirely by bone; the latter is surrounded by bone only at the 
transverse canals (the swellings ["sacs"] occur between these.  Being 
surrounded by bone, I suspect, greatly helps alleviate the need to resist 
being weighed down or crushed by contractions of neck musculature, although 
the problem of air diffusion remains.  To the extent of my knowledge, no one 
has really done good studies to show how air is emplaced or circulated 
through these sacs, though if anyone knows of such a reference, I would love 
to know of it!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Dept of Earth & Environmental Science
University of Pennsylvania
240 S 33rd St
Philadelphia PA  19104-6316
Phone: (215) 573-8373
Fax: (215) 898-0964
E-mail: jdharris@sas.upenn.edu
and     dinogami@hotmail.com
http://www.sas.upenn.edu/~jdharris

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