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Re: Coelurus a maniraptoran (for how long?)



David Marjanovic wrote-

> Why should it have reversed? What evolutionary pressures are there at all
> that can trigger the evolution of new eggshell types? ~:-| ~:-|

Eggshells are just as selected for by environmental pressures as any other
part of an organism.  After all, some evolutionary pressure must have
triggered the evolution of ornithoid eggs from dinosauroid eggs.  Pressures
could include clutch size, nest temperature, nest structure, etc..  I'm no
oological expert, but dinosauroid prismatic (including dendroolithids)
doesn't look that different from ornithoid.  The mammillae simply extend
further distally and the distal portion is prismatic, not squamatic.  I
could think of several reasons segnosaurs might have reversed to a
dinosauroid prismatic morphology- perhaps including a difference in ovary
morphology based on segnosaurs being quadrupedal and/or herbivorous unlike
other theropods, but like other dinosaurs with dinosauroid eggshell.

Mickey Mortimer