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Re: Mesozoic mountains & Spinosaur sails with neighboring critters (2 threads)

Rodlox R wrote-

> and for those who earlier said that there are no examples of unrelated
> creatures sharing an enviroment & evolving something like a sail....in
> modern times, both *Riftia* worms at undersea volcanic vents and at least
> one type of clam that shares the enviroment down there, both lack internal
> organs, and both rely on sulfur-processing bacteria inside them.

There are many examples of two distantly related taxa in an ecosystem
sharing a character not found in other taxa in that ecosystem which are more
closely related to one of the taxa with the trait.  For example,
Struthiomimus and Gorgosaurus both have arctometatarsi, but
Saurornitholestes (more closely related to Struthiomimus) does not
(hypothetically).  But in these cases, the character isn't particular that
ecosystem- it didn't evolve due to Judith River conditions.  The
ornithomimosaur arctometatarsus goes back to Turonian Asia at least, and is
found in many taxa which lived in varying habitats, for example.

It's also important that other more closely related taxa in a given
ecosystem lack the trait (thus showing it's not necessary for that
environment).  So your black smoker example would need another polycheate
which lives there yet has internal organs and a plesiomorphic way of
acquiring nutrition.  Thinking about it further... I suppose lots of
unrelated deepsea fish have photophores, while others that are more closely
related to one of the photophored taxa probably live in the same ecosystem
and lack them.  That could be a counterexample, if the specifics were worked
out.  But the abyssal environment is much larger and more stable than any
terrestrial one.

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