Re: sauropod spines

[Stan Friesen <swf@ElSegundoCA.NCR.COM>]

 From: Scott <HORTON@bcrssu.agr.ca>
 > 
 >   I know that sauropods (family Saurischia) are not supposed to be closely
 > related to Stegosaurs and Ankylosaurs (family Ornithiscia), but there seems
 > to be an uncomfortably large number of convergent evolutionary features in
 > dinosaurs!

Well, not entirely convergent.  Dermal ossicles are a feature of
many thecodonts - as well as crocodilians.  Alterations of the
dermal ossicles to meet the particular needs of each group is not
really too surprising, nor is a slight level of convergence in
the forms taken by the dermal ossicles.

Titanosaurid sauropods actually have dermal *armor*, a little
like ankylosaurs.  (Or at least some of them do, such as Saltasaurus).

[P.S.  Saurischia and Ornithischia are not *families*, they
are orders, Sauropoda is a a suborder - the families are things
like Titanosauridae and Stegosauridae].

 > 
 >   By the way, can someone explain to me why the family that birds evolved 
 > from
 > is named for a lizard-like hip while the family that birds did not evolve 
 > from
 > is named for a bird-like hip? Convergent evolution again?

*Superficial* convergence.  The ornithischian hip looks superficially
like that of birds, but arrives at that appearance in a slightly
different way.

Where in birds one bone is *rotated* backwards, the ornithischians
have a backwards growing *spur*.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.