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RE: Warm southern winters




-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Dann Pigdon
Sent: Wednesday, July 24, 2002 2:32 PM
To: DML
Subject: Re: Warm southern winters


"Tracy L. Ford" wrote:
>
>
> The prevailing theory about the Koonwarra fish beds is that the
> creatures died when a shallow section of the lake froze over, either
> freezing the animals to death or, more likely, cutting off their oxygen
> supply.<<
>
> What about an algae, or some other thing cutting off the oxygen supply?

The presence of siphlonurid mayflies and cantharid beetles suggest cool
conditions, and although some people reject the idea of winter ice, the
most convincing arguement so far seems to be the thanatoceonose theory
(a shallow lake margin freezing over and cut off from the main lake body
by some sort of obstruction like a sand bar, resulting in a lack of
oxygen). Note that this doesn't mean the entire lake froze over. It may
have just been some of the shallow margins, which I would imagine can
occur at just a few degrees below zero (and in a fairly short length of
time).<<


Ahh, I think I can live with that.

> Ferns are dominate? Why not a temperate climate? Why ignore the plants?

No-one ignores the plants. They suggest a MAAT of around 10 degrees
celsius, which makes sub-zero temperatures during mid winter a distinct
possibility. This estimate just doesn't fit with the other lines of
evidence, though.

> Hey, is there a map showing the Cretaceous land masses for Australia like
> they have for the Late Cretaceous inland sea? That'd be great to see.

I recently downloaded a PDF from the Science website (for free - it's
more than a year old) that was extremely interesting:

Michael Gurnis, R. Dietmar Mu¨ ller, Louis Moresi 1998 "Cretaceous
Vertical Motion of Australia and the Australian-Antarctic Discordance"
Science 279:1499-1504

Register free with Science and anything more than a year old is FREE!
You can't argue with that.<<



Yea, but I like to have a photo copy, sometimes the printer just doesn't
print the paper well enough...

> Personally I'd go with the plants. These can be tested today. If the other
> physical evidence is geologic, then there may be another interpretation
than
> the one that is currently thought. We know more about what's living today
> than we do in the past.

This is always possible. However, once again you've hit the nail on the
head: "We know more about what's living today than we do in the past."
Although even that may not be true (I've heard it said that more
research has been done on extinct reptiles than on their extant
relatives).<<



I find it amazing at times when it turns out that the paleontologist, who
want to know more about the past has to do research on living animals
because the zoologist haven't done the research. How the furcula of a bird
really works and Larry Witmers current research to name a few.

>
> and if the world was warmer than it is today then a cold poles would be
out
> of the norm.

Certainly you wouldn't have had anything like modern polar conditions.
But I'm guessing sub-freezing temperatures during the winters can't be
ruled out completely (if only JUST sub-zero, by a few degrees). Keep in
mind I'm talking celsius here. No-one would strongly suggest zero
degrees fahrenheit.<<



Ok, I think I can go along with that.

--

I've posted more messages to the DML in the last couple of days than any
similar time period in the past. I even got timed out for a day for
posting too many. How cool is that? :)

--

Tracy L. Ford
P. O. Box 1171
Poway Ca  92074