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Re: Mass extinction



On Sat, 8 Mar 1997 08:56:31 -0500 "Michael" <tons@ccs.netside.com>
writes:
>As I understand it, except for a few marine(sharks) and land 
>animals(?crocs) most everything large went extinct.  Is that a 
>correct assumption?  What were the smaller marine and land animals 
>that went extinct?  I have read different answers.<

Not entirely.  Lots of small stuff went too. Small marine animals that
went extinct were "particular kinds of marine plankton"(most calcareous
plankton and many planktonic foraminiferans), ammonoids, "certain kinds
of snail-like molluscs, gastropods, bivalves," rudists, and I assume
there may have been small species of mosasaurs and plesiosaurs as well as
the large ones that went extinct.  Steven Stanley says that the
Cretaceous event's "effects in the ocean were far less devastating than
those of the terminal Permian event, which eliminated more than twice as
large a percentage of marine families."  See the Stanley references below
for more critter and climate details.

Stanley doesn't mention, and I haven't found a good a list of small land
animals that went extinct, except for any small Cretaceous dinosaurs --
would love to have a list if anyone out there can give me a good
reference.

>I am not sure about receding seas, especially inland, as 
>happening in the late cretaceous, either. That would have caused 
>world wide changes, but did it happen?   Are we sure there were less 
>numbers of dinosaur species worldwide at the end of the Late 
>cretaceous or only in NAmer?

Stanley says the sea level by the Late Cretaceous "stood higher in
relation to most land areas than it had during the Early Cretaceous." 
Then later, "Just before the end of the Cretaceous Period, the seas
retreated southward from the interior [North American] seaway and the
Mississippi Embayment, and a new pulse of mountain building began."
(p.502, 514).  But I've also seen it argued that world wide climate
changes were happening at the Triassic-Jurassic boundary too, and dinos
adapted to that, so why go extinct over changes in the Cretaceous?  Let
me preface the following with the statement that I am no weather expert. 
Today's continental style weather is characterized by extremes in the
wet-dry and hot-cold continuum.  Today's coastal style weather has less
of this extreme swing.  Were there extreme wet-dry or hot-cold seasons
then? If Continental style weather was replaced by coastal style weather,
what was the big climate shift?  I don't have a good list of Late
Cretaceous dinosaurs up to the boundary.  I've seen it argued that
dinosaurs were already on the decline in diversity heading towards the
K-T boundary.

>Do you know how to get in touch with Thomas Crowley or Gerald North?  
>They wrote a monograph called "Paleoclimatology"?

I'm afraid I don't.  It sounds like it could clear up a lot of my
questions too!

Refs:
Sylvia J. & Stephen A. Czerkas, 1995, "Dinosaurs: A Global View", Barnes
and Noble Books

"DINOSAURS!: Volunteer Training Materials." Prepared by Eileen Flory, 
The Science Museum of Minnesota. Summer 1986.

Steven M. Stanley, 1987, "Extinction," Scientific American Books, Inc.,
NY

Steven M. Stanley, 1989, "Earth and Life Through Time, second edition, W.
H. Freeman and Company, NY

Judy Molnar
Education Associate
Virginia Living Museum
vlmed@juno.com
jamolnar@juno.com