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Re: AW: 'Eggless' chick laid by hen in Sri Lanka




----- Original Message -----

> From: evelyn sobielski <koreke77@yahoo.de>
> To: dinosaur@usc.edu
> Cc: 
> Sent: Friday, 20 April 2012 10:06 AM
> Subject: AW: 'Eggless' chick laid by hen in Sri Lanka
> 
> 
>>  He found that the fertilised egg had developed within the
>>  hen's reproductive system, but stayed inside the hen's body
>>  until it hatched.
>> 
>>  A post-mortem conducted on the hen's body concluded that it
>>  died of internal wounds.
> 
> This is why crown dinos are highly unlikely to evolve (ovo)vivipary form the 
> present state. The eggshell has simply become too tough; breaking it will 
> usually fatally injure the oviduct or cloaca (a common complication in egg 
> binding). Herptiles OTOH have softer-shelled eggs; ovovivipary has evolved 
> many 
> times there.
> 
> Of course, the tougher eggshell gives benefits. This case might make a nice 
> classroom example for evolutionary trade-offs.
> 
> 
> Regards,
> 
> Eike
>

++++++++++++++++++++++++++++++++++++++++

"Soft-shelled'  eggs are a hallmark of most lepidosaurs and some turtles (even 
then, the structure of the Tuatara eggs is more similar to a gecko than an 
iguana).  Crocodylians, geckos and most turtles lay hard-shelled eggs. I don't 
think the apparent problem with getting viviparous archosaurs had anything to 
do with the egg cracking inside the oviduct, as theoretically, the "egg" of an 
ovoviviparous archosaur would not have been calcified. The bigger problem seems 
to be in figuring out how to get calcium to the hatchlings if they don't pull 
it from the eggshell.

This news story is really just about a freak case of egg-binding that happened 
to make it full term.

Jason