re: why sharks didn't go extinct

[@lepomis.psych.upenn.edu, @uga.cc.uga.edu:Schwimm@USCN.BITNET (Paleontology Columbus College, Georgia)]

Let me add to the good points by Stan Friesen:

Assuming the K/T boundary events were impact driven (I don't, but let's for
this argument), few of the hypothetical efgfects would affect sharks; they are
fairly tolerant of variable salinities, many are normally living in deep (below
Zone) water and the darkness scenarios would be less likely to affect the  them,
  Perhaps more to the point, there were major changes in sharks across the
K/T boundary, including a few I work with.  For example, one of the most importa
Ualicorax, globally distributed and comprising dozens of species
from Albian to Maastrichtian (latest Cretaceous) apparently disappears at
 the K/T boundary.  And Cretolamna, also very widespread and long-lived,
seems to anagenetically evolve into the Paleocarcharodon-Carcharodon
stem.  (Seems is necessary with sharks, because most of the detailed
taxonomy is based on teeth, which are possibly deceiving).

  If you will,  "sharkkind" doesn't appear to dramatically change at the
boundary,  but if one looks at detailed lineages, they do indeed change.
By the same token, if we consider dinosaurs and aves as part of the same
class (I do), then we have a similar level of change.  The difference is that
Paleocene and later sharks externally resemble Cretaceous sharks (big,
streamlined, etc.) whereas Cretaceous Dinosauria obviously don't resemble
post-Cretaceous Aves.  It may have more to do with the functional
morphology of sharks than anything else, and the resemblance of pre- and
post-K/T taxa is in large part convergent:  one must be a big, sharp-toothed
streamlined fish to behave as a shark,  and given the ancestry of the
end-K survivors, there was little chance that post-K sharks could
look much different from their ancestors.

david schwimmer
Columbus College