Post-Triassic Bellerophontids?

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Is anyone aware of the existence of post-Triassic Bellerophontids?  This 
is an area in which I have no expertise, but earlier this week I was 
poking around in some very dark gray shales underlying the gypsum beds 
(Late Jurassic) at Fort Dodge, Iowa.  These shales are very poorly 
fossiliferous, but did produce a few Bellerophontids.  The shale appears 
to be associated with the gypsum, but may be Pennsylvanian in age.  I am 
in the process of running samples for conodonts and palynomorphs, but 
earlier runs of this shale were nonproductive.  The Bellerophontids seem 
to support a Pennsylvanian age, but I would like to make sure that I am 
not overlooking the existence of younger members of this group.  Any 
help will be appreciated.  Thanks!

          Curt Klug (cklug@blue.weeg.uiowa.edu)