ammonites vs. fish at K-T

["Ken Kinman" <kinman@hotmail.com>]

John,
    Cephalopods suffered terrible losses at K-T.  Ammonites were already in 
serious decline anyway and K-T just finished them off.  Cephalopod babies 
are very dependent on plankton, and only a few of the more generalist 
feeders among them managed to make it through by scavenging---namely the 
nautilus and several coleoid groups (cuttlefish, squids and octopei).  
Probably a minimum of 7 clades (i.e., at least 7 species of cephalopods) 
made it.
     Fish on the other hand were not in decline (like ammonites were).  And 
many baby fishes are comparatively less dependent on plankton (more 
generalist), so relatively fewer clades of fishes were wiped out at K-T than 
among cephalopods (probably an absolute minimum of 35 actinoptergyian fish 
clades survived, probably more).  But even the surviving fish groups would 
have suffered huge population losses (as did almost all groups or organisms 
except decomposers like bacteria).  It may be difficult to figure out why 
some groups survived and others didn't, but I don't think it is 
overwhelmingly difficult to find plausible explanations.
                      -----Ken Kinman
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