Re: sacral vertebrae

[Stanley Friesen <sarima@ix.netcom.com>]

At 02:28 PM 6/14/98 -0600, chris brochu wrote:
>Ladies and Gentlemen,
>(FWIW -
>crocodylians almost never increase the number of sacrals during 
>ontogeny. It happens, but it's rare.  Normally, they hatch with two 
>and die with two.

Yep, more or less as expected - two sacrals is the ancestral condition for
archosaurs.  Dinosaurs generally have at least three sacrals as an adult (I
think this was originally one of the defining characteristics).  And adult
sauropods have even more.


Actually, it is interesting that some crocs develop a third sacral!  this
shows that some variation in sacral number is quite normal in archosaurs,
and suggests how the increase in number in dinosaurs started to evolve.

--------------
May the peace of God be with you.         sarima@ix.netcom.com
                                          sfriesen@netlock.com