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Re: Extinction once again



> > Yet the extinction was global.
> 
> Lest we take news reports too literally, we should remind ourselves that
> extinction is only recorded in one location!

Everywhere outside Montana, Alberta etc., all those animals and plants
survived? :->

> > 4. Lots of terrestrial egg-laying vertebrates survived (turtles, crocs,
> > lizards/snakes, tuataras, monotremes...)...
> 
> They are mostly very small and can hide their nests in a greater variety
> of places.  Crocs are totally dependent on wetlands, though.

Just what I say!

> > 5. Marsupials, for example, were severely hit. How come?
> 
> Their extinctions are timed to placental radiation at the K/T.  So
> replacement is a thoroughly respectable hypothesis for this.

Nope. Do you know how old the youngest recorded marsupials here in Austria
are? 17 million years. In the Miocene we still had possums, and AFAIK the
cause for their extinction is totally unknown. North America has a similar
pattern AFAIK, and marsupials have got into Africa sometime in the Tertiary. The
pattern of South America, where marsupials and placentals immigrated together
sometime around the K/T, is probably known to most list members -- the
placentals were all ungulates* and stayed herbivores, while the marsupials 
evolved
insectivores and carnivores. (Later arriving rodents, monkeys and procyonids
[racoon etc.] filled niches that were previously empty.) Sometime around the
Great American Interchange (or before? or after?) the South American ungulates
died out, as did the marsupial carnivores and the sebecid crocs, while the
opossums migrated north and still continue to do so.

*Xenarthrans = edentates = "paratheres" may have been present in South
America during the Late Cretaceous AFAIK; there is one from Paleocene China and 
an
anteater (Eurotamandua) from Eocene Germany.

Possible ungulate teeth from Eocene Australia are known.

The phorusracids, the third group of top carnivores of Tertiary South
America, migrated northwards and survived well into the Pleistocene in both 
North
and South America, when they succumbed to the end-Ice Age megafaunal
extinctions which were probably caused by the immigration of humans. (Same for 
ground
sloths.)

In short, I'd be very, very, very careful to suggest competition as cause
for extinctions (which does occur, it just seems to be rarer than thought), let
alone mass extinctions.

> Why wouldn't
> diverse creatures have diverse reasons for their disappearance--

Perfectly good argument, but not if, as at the K-T boundary, _large clades_
died out _around the globe_ _in nearly all ecosystems_ _at the same time_!!!

> > 6. Plankton (and all animals with planktonic larvae) was severely hit,
> which
> > is not easy to explain with a regression.
> 
> Not yet timed to terrestrial extinctions.

May I suspect that your references are _terribly_ outdated (10 years old or
more)? One and the same iridium-enriched clay layer is found around the world
(even at least 2 outcrops in Austria) in/on all kinds of sediments,
terrestrial, marine, whatever, on continents, in deep-sea drill cores... It has
become the definition for the K-T boundary! A millimeter-sized scrap of a
meteorite has been found in this layer in the Pacific.

One last word, er, paragraph :-] on the speed of that extinction:
www.dinosauria.com mentions somewhere that 80 % of all pollen in Montana died 
out
within _2 CENTIMETERS_ (not 200, not 20, two) below the K-T boundary, and we can
easily make the Signor-Lipps effect responsible for the 2 instead of 0
centimeters B-) . The most recent count of dinosaur fossils there (1999 AFAIK)
yields similar results, plus the *Triceratops* skull 1.8 m below the boundary,
which only confirms what the hadrosaur tracks _37 centimeters_ below it suggest.

Congratulations to HP Ken Kinman for his post on this subject!

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