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K-T Marine Extinctions



Some thoughts on the somewhat-less puzzling, marine extinctions of the K-T:

Among the main groups to suffer (either extinction or massive diversity
crash) at or prior to the boundary are:
Inoceramids (total extinction)
Ammonoids (total extinction)
Rudists (total extinction)
Mosasaurs (total extinction)
What remained of Plesiosauria (total extinction)
Coccolithophorids (diversity crash)
Planktonic Foraminiferans (diversity crash)

and a few others I can't think of off the top of my head.

In contrast, decapod crustaceans (crabs, lobsters, etc.), burrowing
bivalves, teleost fish, echinoids, etc. don't seem to have suffered much, if
at all.

One possibility I have heard suggested, which doesn't seem unreasonable, is
that this pattern matches a crash in the phytoplankton-based part of the
marine food web, but not in the detritivore-based part of the marine food
web.  That is to say, some factor (changes in oceanic circulation due to the
Maastrichtian Regression? reduced insolation (not insulation) from impact?
both?) brought about a massive decrease in productivity in phytoplantkon.

Those animals which fed on phytoplankton (inoceramids, if any were left in
numbers after their mid-Maastrichtian diversity crash; rudists; ammonoids,
interpreted as planktonivores rather than carnivores by Seilacher) and those
forms which ate these, and so on, died out do to the loss of the food supply.

On the other hand, bottom-feeding organisms and the animals who ate them
(tomorrow, on Jerry Springer... :-) would be less directly affected by
temporary cessation of phytoplankton productivity.

Just some food for thought.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661