live births in birds -Reply

[JNorton@MAILBOX.UNE.EDU]

Leathery eggs with flexible shells would collapse inward following a
net loss of volume (water) from the eggs and would not support an air
space.  In the absence of an air space, parabronchial air capillaries
could not develop as they do in modern birds.  Leathery eggs do not
rule out an avian-type fixed-volume lung with an air sac system, but
such eggs make it unlikely that the air capillary structure was
present.  It is the presence of air capillaries that allows modern
birds to sustain such high rates of metabolism.

James M. Norton, Ph.D.
University of New England
11 Hill's Beach Road
Biddeford, ME  04005
phone: [207]283-0171 x2270
fax: [207]283-3249
email: jnorton@mailbox.une.edu