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Cretaceous Mass Extinction

Recently you wrote:"In the sea, it must have been a scavenger's paradise.
 Horseshoe crabs and sharks are scavengers."

They are also predators.  I would think after the first flush of death,
the sharks would be in trouble, because if much of the plankton dies, the
food chain collapses and the hardest hit would be a top predator like a
shark.  Plankton feeding sharks would especially be in big trouble. 
Horseshoe crabs may have been protected because of their bottom feeding
habits, since Stanley mentioned in his books that bottom-feeding forms of
some groups seemed to be the ones to make it through vs more pelagic
forms.  The bottom may have been an insulated environment in that regard.
 Also, horseshoe crabs go through a regular torpor during the last fall
and winter.  They may have been able to wait out the major impact

"Ah. This is good for adaptive radiation and the formation of new
phylogenetic groups."

Of course.  But my question concerned groups that were already
established, some for eons, surviving across the boundary, while others
in the same category did not.  Sharks, brachiopods, and horseshoe crabs
have changed little since they started back in the Paleozoic; most
brachiopods didn't make it, the other 2 groups did make it through into
the Cenozoic.  Dinosaurs rose in the Triassic, survived the extinctions
of the Triassic and Jurassic, but don't make the Cretaceous boundary. Why
didn't they adapt that last time?  Adaptive radiation doesn't answer my
question entirely.

"You are not alone."

I take comfort from that and from everyone being so kind to answer.  Any
one that can expand my list of animals that made it through vs didn't
make it through the K-T boundary, your contributions are greatly
appreciated.  Thanks to all that have responded so far, and will continue

Judy Molnar
Education Associate
Virginia Living Museum