Re: beaks and teeth

[William Hinchman <bsaurus@bellatlantic.net>]

Sherry Michael wrote:
> Snip
> How about "egg teeth"? I've always assumed that they were an old trait that
> now had a different purpose. Are "egg teeth" even the same kind of structure
> as actual teeth or are they some sort of psuedo tooth?


Egg teeth are not actually teeth at all, but a protuberenace on the
beak.  As the time
of hatching nears, the Co2 level inside the egg goes up, as the embryo
is using more
oxygen than the semi pourus egg shell will allow through.  A muscle on
the back of the
birds neck begins to twich, which aloows the "egg tooth" to poke a hole
in the shell.
After a hole is made, the embryo relaxes, until the process repeats
itself.  This of 
course is a highly simplified version of events.  I believe the Ostrich,
and perhaps
several other species of extant birds have no egg teeth, and the
brooding pair has to
assist them out of the shell.