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RE: feathered ornithopods?
What effect or modifications would vegetation have on the climate at that time?
>>> "Williams, Tim" <TiJaWi@agron.iastate.edu> 07/19/02 09:26AM >>>
Tracy Ford wrote:
> I don't buy this polar winters theory.
I think we can be pretty sure that both the Earth and the Sun were in the
same relative positions as they are today (give or take), and that the Earth
tilted on its axis as it orbited the sun. Therefore, that part of the
planet near the poles would be exposed to prolonged darkness during the
winter season - including the southeastern portion of Australia (see below),
which was just a stone's throw from Antarctica. Sure, the Mesozoic was
warmer than today - but does anyone doubt that areas within the Antarctic
(and Arctic) circles during the Mesozoic had winters that were not as long
and dark as modern Earth's polar winters. That's got to have an effect on
temperature (i.e. downwards).
> The paleo botanist shows a warm climate.
All year round? The vegetation here in Iowa changes from lush to skeletal
in the space of 6-8 months.
>The thing is Australia was always in the lower southern hemisphere.
> Cambrian to now.
The last time I looked Australia was in the *upper* southern hemisphere.
Cape York, at the extreme north, is a little more than 10 degrees from the
Equator. The Australian continent stretches from around 10 to 45 degrees
latitude South, approximately the same latitude as for modern-day southern
Africa and around three-quarters of South America. Southeastern Australia
(where I was born and raised) is now at about the same latitude as Uruguay
and South Africa.
Back in the Early Cretaceous, Australia is estimated to have been positioned
between around 50 and 85 degrees latitude South - well within the modern
Antarctic Circle (~ 66 degrees). Quite a shift comapred to today. (On the
flipside, modern Greenland, Siberia and most of Canada resides within 50 and
85 degrees latitude North.)
> Placoderms, eurypterids, ammonites, mosasaurs, plesiosaurs, sauropods,
> labyrinthodons, theropods, you name it, lived in Australia way down
Yep, but most of these critters lived in the sea. Also, nobody has argued
that prolonged cold temperatures is an obstacle to the existence of life;
only that polar dinosaurs may have special adaptations for enduring the
winter cold - such as insulation, or migration.
> I don't get why the Early Cretaceous is specifically targeted for
> being 'cold' when all the time period it was down there.
I don't believe it is the case that Early Cretaceous Australia is being
specifically targeted as 'cold'. It's just that the Mesozoic terrestrial
fossil record from Australia is heavily biased in favor of this time
(Aptian-Albian) and place (SE Australia), so most discussions on this topic
are centered on the Eraly Cretaceous. The Aussie hypsilophodontids and
Koonwarra feathers, for example, both share this provenance.
Timothy J. Williams, Ph.D.
Iowa State University
Ames IA 50014
Phone: 515 294 9233
Fax: 515 294 9359