pterosaur tracheal rings

["James R. Cunningham" <jrccea@bellsouth.net>]

To all:
Does anyone know if evidence has ever been found for cartaliginous
tracheal rings in any pterosaur?  If so, can you direct me to
references? I would expect a selective pressure toward their development
in order to assist in recovering from the oxygen deficit incurred during
takeoff.
Thanks,
                Jim Cunningham
                jrccea@bellsouth.net
                jrccea@juno.com

I prefer the juno.com address.  I open it more often, and it has a spell
checker, which makes life much easier for everyone I communicate with. 
JimC