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Re: Spinosaurs as what?



T. Michael Keesey wrote:

>_Ouranosaurus_ was already mentioned, and _Rebbachisaurus_ had long
>vertebral spines as well: three dinosaurs from distinct lineages
>(_Spinosaurus_ a theropod, _Ouranosaurus_ and ornithischian,
>_Rebbachisaurus_ a sauropodomorph) with the same trait, all living at
>the same time and in the same place. Coincidence? Not likely.

Actually, very likely in my mind.  For one thing, the taxa were NOT
contemporaneous.  Spinosaurus is from the Cenomanian Baharija Formation of
Egypt, Rebbachisaurus is from the Albian Tegana Formation of Morocco, and
Ouranosaurus is from the Aptian Elrhaz Formation of Niger.  Elrhaz
spinosaurids and rebbachisaurids are Suchomimus and Nigersaurus,
respectively, neither of which have very high neural spines.  The Baharija
has large theropod dorsals (Bahariasaurus?, Deltadromeus?) without tall
neural spines.  And even if they were contemporaneous, I can't think of an
ecosystem today where a few unrelated taxa (but not other taxa which are
more closely related to one of the taxa in question) all evolve a trait for
a common purpose.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html