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Egg-types and Taxonomy?

I've been looking through "Dinosaur Eggs and Babies," and hev come across
Figure 10.2.  This shows the basic types of dinosaur eggs and what groups
that they've been atributed to.  There are basically three types of Dinosaur
eggs: Dinosauroid-spherulitic, Dinosauroid- prismatic, and Ornithoid.  The
D.-S. eggs have been atributed to Sauropods and Ornithischians, the D.-P.
eggs to some ornithopods and marginocephalans, and the ornithoid eggs to
theropods and birds (duh).  Anyways... I was thinking, if saurischia really
was monophyletic, shouldn't sauropod eggs be in a group be themselves,
different from the theropods' and ornithischians' eggs?  But on the other
hand... if phytodinosauria was monophyletic shouldn't sauropod and
ornithischians be more similar to eachother than they are to theropod's
(which they are)?  The cladogram that follows is of a phytodinosaurian
arrangement of the dinosauria.  

T  S  O
 \   \  /
   \  /

It would make more sense to me to have the D.-S. eggs grouped together in a
monophyletic taxa, rather in a paraphyletic taxa, as such:

T  S  O
  \ /   /
    \ /

If dinosaurs really evolved this way, then there should be at least some
similarities between sauropod and theropod eggs, rather than the unlikely
scenario of sauropods retaining a primative feature entirely unchanged.


Peter Buchholz